Model Chemistry Study Of Choline And Urea Based Deep Eutectic Solvents

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2018

Model Chemistry Study Of Choline And Urea

Based Deep Eutectic Solvents

Libby Nicole Kellat

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MODEL CHEMISTRY STUDYOF CHOLINE AND UREA BASED DEEP

EUTECTIC SOLVENTS

LIBBY NICOLE KELLAT

BachelorofSciencein Chemistry

Cleveland State University

May2010

Submitted in partial fulfillment of requirements forthe degree

MASTEROF SCIENCEIN CHEMISTRY

at the

CLEVELAND STATE UNIVERSITY

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We hereby approvethisthesis for LIBBYNICOLEKELLAT Candidate fortheMaster’s degree for the

Department of Chemistry

andthe CLEVELAND STATE UNIVERSITY’S

College of Graduate Studies by

Committee Chairperson, Dr. David W Ball

Department & Date

Committee Member, Dr. JohnF Turner

Department & Date

Committee Member, Dr. Warren Christopher Boyd

Department & Date

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ACKNOWLEDGMENT

I would like tothankmy advisor Dr. David W Ball for givingmetheopportunity to expand my knowledge base into the realm of computational chemistry. His guidance

and encouragement throughoutthe research process made progresspossible. His patience through semesters off, lost data, andrestarting my research with a new topic wasgreatly

appreciated. In the end, the experience andknowledge I have gainedfrom thisproject

was wellworththeyears spent creating it.

I would like tothankmy family for encouraging meto learn and explore new topics throughout myentirelife. My familysupported STEAM education, which laid the

groundwork for my artistic and scientific endeavors. I am ever grateful for your support; past, present, and future.

I would like tothankmy friends andcolleagues, especially Joy and Chris, for supporting and encouraging me throughout thisjourney. Their support ranged from

listening to medrone on about my research, to encouraging words andnotes, to keeping

me on trackto meet my goals/deadlines, tomaking sure that I was taken care of

physically and emotionally.

It has been a long and winding road. Completing this degreewouldnot have been possiblewithout theoverwhelming love and support from myvillage (family, friends,

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MODEL CHEMISTRY STUDYOF CHOLINE AND UREA BASED DEEP

EUTECTIC SOLVENTS

LIBBY NICOLE KELLAT

ABSTRACT

Gaussian and GaussViewsoftwarewere utilized to characterize interactions

between choline saltsand urea, which form a deep eutecticsolvent(DES). The initial

system studied was choline chloride and urea, at a 1:2 molar ratio, which is also known as

reline. Subsequentsystems, substituting the chloride anion with other anions (fluoride,

bromide, andhydroxide),were studiedto showthatthe systemwith greater calculated strength of interaction will have more non-ideal physical properties, such as meltingpoint (found inliterature). Observations regarding structure relatedto counterion electron

density andhydrogenbondingwere made throughoutthe studies.

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TABLE OF CONTENTS

Page

ABSTRACT...iv

LIST OF TABLES...vii

LIST OFFIGURES...viii

CHAPTER I. Background...1

1.1 Chemical Background...1

1.2 Model ChemistryBackground...3

1.3 Summary of Research Studies...5

1.4 Model ChemistryData Analysis...6

II. Choline Chloride Study...7

2.1 Procedure...7

2.2 Choline Chloride withOneUreaMolecule...8

2.3 Choline Chloride withTwoUrea Molecules...15

2.4 Results... 25

III. Gaussian Revision Comparison Study...27

IV. Counterion Substitution Study...35

4.1 Procedure...35 4.2 Fluoride Substitution...36 4.3 Hydroxide Substitution...40 4.4 BromideSubstitution...44 4.5 Results...47 v

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V. Choline Fluoride Study...53

5.1 Procedure...53

5.2 CholineFluoride withOneUrea Molecule...54

5.3 Choline FluoridewithTwoUreaMolecules...62

5.4 Results...70

VI. Conclusion...72

BIBLIOGRAPHY...74

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LIST OF TABLES

Table Page

I. Choline Chloride withOne Urea Energyof FormationCalculations...14

II. Choline Chloride withTwo UreaEnergy of Formation Calculations...23

III. Choline Chloride withOne UreaTotal Energyof Formation...26

IV. Choline Chloride withTwoUreaTotalEnergyof Formation...26

V. Local to OSC FrequencyandEnergy Comparison...28

VI. CholineFluoride Total Energy of Formation Compared to Choline Chloride...40

VII. Choline Hydroxide Total Energyof Formation Compared to Choline Chloride...44

VIII. Choline Bromide Total EnergyofFormation Compared to Choline Chloride...47

IX CounterionSubstitution Study Bond Length Comparison...49

X Distance Between Atomsin Choline Salts...51

XI. Length of C=O HO Hydrogen Bond...51

XII. CounterionSubstitution Study TotalEnergyof Formation...51

XIII. CounterionSubstitution Study TotalEnergyof Formation Difference... 52

XIV. CholineFluoride with OneUreaEnergy of Formation Calculations...61

XV. CholineFluoride with TwoUreaEnergy of Formation Calculations...69

XVI. CholineFluoride withOneUreaTotal Energy of Formation...71

XVII. CholineFluoride with TwoUrea Total Energy of Formation...71

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LIST OF FIGURES

Figure Page

1. Choline Chloride with Urea#1...9

6. Choline Chloride with Urea#3 & #1...16

11. Choline Chloride with Urea#6 & # 1...21

13. Local Comparison Number 1...29

14. OSC Comparison Number 1...30

19. Choline Fluoride with Urea#5 & #2...37

20. Choline Fluoride with Urea#3 & #1... 38

21. Choline Fluoride withUrea#3 & #2...39

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22. Choline Hydroxide with Urea #5 & #2...41

23. Choline Hydroxide with Urea #3 & #1...42

24. Choline Hydroxide with Urea #3 & #2...43

25. Choline Bromide withUrea#5 & #2...45

26. Choline Bromide withUrea#3 & #1...46

27. Choline SaltAtom Numbering...50

28. Choline Fluoride with Urea #1...56

29. Choline Fluoride with Urea #2... 57

31.Choline Fluoride with Urea #4...59

33. Choline Fluoride with Urea #2 & #1...63

34. Choline Fluoride with Urea#2 & #2...64

35. Choline Fluoride withUrea #2 & #3...65

38. Choline Fluoride with Urea #4 & #3... 68

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CHAPTER I

Background

1.1 Chemical Background

A eutectic is a homogenous chemicalmixture where themixture’s freezing

(melting)pointis lower than thatof the individual components (1). Deep eutectic

solvents(DESs) are more extreme examples ofeutectics,wherethe freezing point

depression ismore non-ideal,generally makingthemliquids at room temperature.Reline, a DES commonly studied in literature, has a melting pointof 285 K, whiletheindividual components choline chloride (C5H14C1NO) andurea (CH4N2O)have melting points of

575 K and406 K respectively(2, 3).

Atypical DES composition is anorganic salt, which acts as a hydrogen bond acceptor, and ahydrogenbond donor, suchasurea, an amide, a carboxylic acid, or a polyol. A particular molarratio for each systemwill produce DES properties. Other

molar ratios will notexhibitthe same level of non-ideal interactions (4). Many DESs have the abilityto form three types of hydrogen bonds; neutral, ionic, and doubly ionic

hydrogenbonds dueto thepresence of neutral, cationic, and anionic components in the

system. Neutralhydrogenbonds occur between two neutral components. Ionic hydrogen

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bonds occur betweena neutral component and anionic component. Doubly ionic

hydrogenbonds occur between two ionic components (5).

Traditionallyfluorine, nitrogen, and oxygen arethe elementsthat can participate

in hydrogen bonding.Additional elements, such as chlorine, are included in this discussiondue to an expanding definition of hydrogenbonding (6) andthe data (bond strength andbond length)providedbyAshworth et al. (5).AccordingtoArunan et al. (6) the definition of hydrogen bonding is as follows:

The hydrogen bondis an attractive interaction between a

hydrogen atom from amoleculeora molecular fragment X-Hin which Xismore electronegative than H, and an

atom ora group of atoms inthe same ora different

molecule, in which there is evidenceof bond formation.

In addition, several criteria are given for hydrogenbondformation, including topics of

geometry, physicalforces,and spectroscopy. It is noted thatthe criteria list may expand

over time dueto evolving understanding of hydrogenbondingand increasing testing capabilities (6).

DESs are becomingincreasingly useful in industrial applications as an analog of ionic liquids (ILs), which are lowmeltingpoint salts (formerly, arbitrarily less than

373 K) composed entirely of discrete ions (5, 7). ILs are currentlybeingused formany

applications where DESscan also be utilized. Some of these applications aremetal

processing, metal electrodeposition (chrome, aluminum, copper, nickel, zinc, alloys, composites, etc.), metal electropolishing, metal extraction,processingof metaloxides, and synthesisapplications (7, 5).

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DESs have similar properties to ILssuch as low vapor pressure, powerful solvent capacity, highelectrochemical conductivity, high viscosity, high surface tension, etc. (3,

8)but differ by havinglower production cost dueto lower raw materialcost, being

produced at high purity, and being easierto produce in large scale batches (1, 7, 10). In

contrastto ILs, DESs are tunable and can be chemically customized forthe specific chemical application (7, 77).

Though manyhave hypothesized that DESs wouldbe greener optionsthanILs

with regard to toxicityandthe environment, this may not be thecase. The assumption was made based on the individual components, notthe DES system which has special

properties that arenot present inthe individual components (7).

1.2 Model Chemistry Background

Gaussian 09 Rev D.01 (72),Gaussian 09 RevE.01 (73), andGaussView 5.0.9

wereutilized inthe characterizationofseveralcholine saltand urea systems.

Optimizationand frequency calculations werecompleted using theHartree-Fock (HF)

method andthe 6-31G(d,p)basis set. TheGaussian softwareutilizestheSchrodinger

equation to define the collection of particles inamolecule as a wavefunction, allowing various properties to be defined (14).

Hartree-Fock theory makes assumptions with respectto molecular orbitals,

electronic spin, basis sets, andthevariationalprincipleto simplifytheSchrodinger

equation calculations, making them applicable tomore complex systems. The molecular

orbital assumption breaks the wavefunction into molecular orbitals, creating a Hartree

product. A Hartree product is a function of theproductof molecular orbitals but isnot

antisymmetric(14).

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The electronic spinneeds to be taken into account toallow for an antisymmetric

function depicted as a determinant for probability density, aFockmatrix. A Fockmatrix

iscomposed ofspin orbitals,theproductofa molecular orbital and a spinfunction. Closed shell (restricted Hartree-Fock) and open shell(unrestricted Hartree-Fock)

methods can be utilized. The closed shell method assumes that the molecular orbitals are doublyoccupied, with two electrons of opposite spin (alpha and beta). The openshell method assumesthatthe alpha andbeta electrons are in separate shells, resulting in two Fockmatrices (14).The closed shell method was utilized for thesestudies.

The basis set mathematically approximates molecular orbitals as a set of functions, which are linear combinations ofone electron functions resembling atomic orbitals. The Gaussian softwarecontainspre-definedbasis sets, which contain a set number and set typesof basis functions. Calculationsare onlycomparable between or within molecular systems if theyare completed usingthe same basis set. The 6-3 lG(d,p)

basis set, used in these studies, is apolarized basis set which uses orbitals with angular momentum greater than whatis needed for the ground state. This basisset addsp and d functions tohydrogenandheavy atoms, respectively (14).

The variation principle states thatthe calculated energyof thewavefunction will always be greater thanthat of the exact wavefunction. Anon-linear, iterative method of

solving the Schrodinger equation, the self-consistent field(SCF)method, is used to find a

solutionthat minimizes the energy of thewavefunction by testing for convergence. In the

process of testingforconvergence, the initial and final orbitals resulting from

calculationsare compared. Convergence has been obtained when the field of the final

orbitalsis equal to the initial orbitals (14).

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1.3 Summary of Research Studies

The following studies were completed to addressthehypothesisthatthe system with greatertheoretical strength ofinteraction will have more non-ideal physical

properties(found in literature). The strengthof interaction was demonstrated through the energyof formation of the DES systems studied.

TheCholine Chloride Study wascompleted to characterize choline chloride and urea, at a 1:2 molar ratio, which is referred to as reline throughout the literature. Initially, systems composed of choline chloride and oneurea were characterized. Then an

additional urea wasadded the most energetically probable systems. This study was used

asthebase for theremaining studies.

During the courseof data collection, calculations moved from being completed on

a local computer to the Ohio Supercomputer Center (OSC). OSCuses a different revision of Gaussian 09, so theGaussian Revision Comparison Study wascompleted toverifythat

any difference, if present, would be negligible.

The onlylimitationto the choline counterion isthat it needs tohave the potential for creating ahydrogenbond (5). Inthe Counterion Substitution Study, the chloride counterion of themost energetically probable output systemsfrom the CholineChloride

Study were substitutedwith fluoride,bromide, andhydroxide. This study was usedto

determine which counterionshould havea full analysis completed like the Choline Chloride Study.

TheCholine Fluoride Study was aresult of the Counterion Substitution Study. Choline fluoride andureawere characterized in the same mannerasthe Choline Chloride

Study.

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1.4 Model Chemistry Data Analysis

Calculations for molecular geometry optimization, to a local energy minimum,

were completed on each system. Experimentally, four convergence criteria dictate if the

system is optimized. The following criteria must beessentially zero: forces on the atomic nuclei, root-mean-squareofthe forces, calculateddisplacement of the nuclei ina

projected next iteration, and root-mean-square of thedisplacement. The Gaussian

software has numerical limits (in atomic units) thatareusedto indicatethatthe criteria

areessentially zero. The maximum component ofthe force must be below 0.00045. The root-mean-square of theforces must be below 0.0003. The calculated displacement must be below 0.0018. The root-mean-squareof the displacement must bebelow 0.0012 (14).

Frequency calculationswere used toverify that the system optimized to a local

energy minimum and to determine electronic and thermal energies. Frequency

calculations need to becompletedon optimized structures,usingthe same basis set used

for the optimizationto be valid. Allfrequency valuesneed to be positiveto ensurethat the system optimizes to aminimum energy in thepotentialenergycurve instead of a saddle point. If a saddle point were present, the number of negative frequencies would

determine the order ofthe saddle point. Electronic andthermalenergies are calculated

within Gaussian usingstatistical thermochemical formulas, assuming a temperature of 298.15 K andpressureof1 atm. The calculation for thermal energyincludes translational, rotational, andvibrationalenergies (14). Electronic andthermal energieswereused to

calculatethe totalenergy of formation of theDES. Todo so, the sumof the reactant

energies was subtractedfrom the sum of theproduct energies. The change inenergy

quantified by this calculationis comparable between all systems studied.

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CHAPTER II

Choline Chloride Study 2.1 Procedure

Calculations were completed fortheCholine Chloride StudyusingGaussian09

Rev D.01 and GaussView5.0.9 on a local computer. Optimizationand frequency

calculations were completed foreach system using theHartree-Fock (HF) method andthe 6-31G(d,p)basis set.

Eachsystemwas checked for convergence, showingthat it has been successfully optimized. If convergence was not obtained, the resulting outputfile was reviewed foran

error or other indication of why the system didnot converge. The output file was altered

and resubmitted as an inputfile for analysis. An example ofa common error was whena “bendfailed for angle”, whichalso provided the threecorresponding atoms in theangle.

The error occurred becausethe atoms made a 180-degree angle, which fails the

calculations dueto the limitations of thecalculations. The adjustment madeinthis case would be to alter the angle of themolecules inquestion sothat it is no longer 180-degrees

and re-submit thesystem for analysis.

Next, frequency values wereverifiedto be positive, showingthatthe system has

reached a local energy minimum, not a saddle point. Ifa saddlepointwas reached, the

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frequency in question was reviewed within the GaussView software. The visualizationof the frequency movement indicateswhatalteration may need to be made to the system to obtain a local energyminimum. The system was then adjusted andresubmitted for analysis.

Once a system was confirmed to beoptimized and at a local energy minimum, the output file was reviewed for energydata. The electronic energy dataisprovided in hartrees and the thermal energy data is providedin kcal/mol. Both energy types were converted toJ/molprior to performingcalculations.

2.2 Choline Chloride with One Urea Molecule

Tobegin, optimization and energy calculations were completed for choline chloride andurea separately. The optimizedurea molecule was placed insevenlocations aroundthe optimized choline chloride molecule, resulting in five visually unique

optimized structures (Figures 1-5).

The electronic andthermal energies, from the Gaussianresults, were usedto calculatethe overall energy of formation (Table I). Table Iis set up as areaction,

showing that Xreactant plus Yreactantyields aproduct. The energies for each

component (fromtheoutput files) of the reaction are shown in line, vertically with the

component. To calculate theenergy of formation the sumof thereactant energies was subtractedfrom the sumof the product energies.

The three urea positions that resulted in visually similarresults, positions#4,#5,

and #7, werealsoconsideredto be numerically equivalent. As a result, of these three positions, only position#5 is considered in thenext set of systems to bereviewed.

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Figure 1: Choline Chloride with Urea #1

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Figure 2: Choline Chloride with Urea #2

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Figure 5: Choline Chloride with Urea#6

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Table I: Choline Chloride with OneUreaEnergyof Formation Calculations Position Energy Type Choline Chloride Energy (J/mol) + Urea Energy (J/mol) →

Choline Chloride Urea

Energy (J/mol)

Energyof

Formation

(J/mol) Choline Chloridewith

Urea #1

Electronic -2,064,350,939.8 -588,113,129.0 -2,652,500,221.9 -36,153.1

Thermal 586,098.9 191,811.3 786,901.6 8,991.4

Total -27,161.7

Choline Chloridewith

Urea #2

Electronic -2,064,350,939.8 -588,113,129.0 -2,652,482,972.4 -18,903.6

Thermal 586,098.9 191,811.3 787,918.3 10,008.1

Total -8,895.5

Urea #3

Electronic -2,064,350,939.8 -588,113,129.0 -2,652,526,319.4 -62,250.6

Thermal 586,098.9 191,811.3 788,048.0 10,137.8

Total -52,112.8

Urea #4

Electronic -2,064,350,939.8 -588,113,129.0 -2,652,524,717.8 -60,649.1

Thermal 586,098.9 191,811.3 786,445.6 8,535.4

Total -52,113.7

Choline Chloridewith Urea #5

Electronic -2,064,350,939.8 -588,113,129.0 -2,652,524,822.9 -60,754.1

Thermal 586,098.9 191,811.3 786,487.4 8,577.2

Total -52,176.9

Urea #6

Electronic -2,064,350,939.8 -588,113,129.0 -2,652,523,851.4 -59,782.6

Thermal 586,098.9 191,811.3 786,361.9 8,451.7

Total -51,331.0

Urea #7

Electronic -2,064,350,939.8 -588,113,129.0 -2,652,524,822.9 -60,754.1

Thermal 586,098.9 191,811.3 786,487.4 8,577.2

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2.3 Choline Chloride with Two Urea Molecules

The three most exothermic results from Table I were selected for the next setof calculations,urea positions #3,#5, and #6. An additionaloptimized ureamolecule was added tothree locations ofeach of the selected choline chloride urea systems.

Optimizationand energy calculations were completed forthe new systems. Urea position #3 resulted in three visuallyunique results. Ureapositions#5 and #6 resulted in two visually unique results each (Figures 6-12).

The electronic andthermal energies, from the Gaussian results, were usedto calculatethe overall energy of formation (Table II). Table II is set up in the same manner

as Table I.

The urea#5 positions thatresulted in visually similar results, positions #2 and #3,

were also considered to be numericallyequivalent. The urea#6 positions that resulted in

visually similar results,positions#2 and #3, were alsoconsidered to benumerically

equivalent. As aresult, of these four positions, onlyurea#5 position #2, and urea #6

position #2 will be considered in following studies.

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Figure 6: Choline Chloride withUrea#3 & #1

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Table II: Choline Chloride with Two Urea Energyof FormationCalculations

Position Energy

Type

Choline Chloride Urea

Energy (J/mol) +

Urea

Energy (J/mol) →

Choline Chloride 2 Urea

Energy (J/mol) Energyof Formation (J/mol) Choline Chloride with Urea #3 & #1 Electronic -2,652,526,319.4 -588,113,129.0 -3,240,695,660.3 -56,212.0 Thermal 788,048.0 191,811.3 987,976.3 8,117.0 Total -48,095.0 Choline Chloride with Urea #3 & #2 Electronic -2,652,526,319.4 -588,113,129.0 -3,240,698,942.2 -59,493.8 Thermal 788,048.0 191,811.3 989,365.4 9,506.0 Total -49,987.8 Choline Chloride with Urea #3 & #3 Electronic -2,652,526,319.4 -588,113,129.0 -3,240,711,019.5 -71,571.1 Thermal 788,048.0 191,811.3 989,394.7 9,535.3 Total -62,035.8 Choline Chloride with Urea #5 & #1 Electronic -2,652,524,822.9 -588,113,129.0 -3,240,653,914.9 -15,963.0 Thermal 786,487.4 191,811.3 987,009.8 8,711.1 Total -7,252.0 Choline Chloride with Urea #5 & #2 Electronic -2,652,524,822.9 -588,113,129.0 -3,240,688,335.2 -50,383.3 Thermal 786,487.4 191,811.3 986,880.1 8,581.4 Total -41,802.0 Choline Chloride with Urea #5 & #3 Electronic -2,652,524,822.9 -588,113,129.0 -3,240,688,335.2 -50,383.3 Thermal 786,487.4 191,811.3 986,884.3 8,585.6 Total -41,797.8

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Table II (continued): Choline Chloride with TwoUreaEnergyof Formation Calculations

Position Energy

Type

Choline ChlorideUrea

Energy (J/mol) +

Urea

Energy (J/mol) →

Choline Chloride 2 Urea Energy (J/mol) Energyof Formation (J/mol) Choline Chloride withUrea #6 & #1 Electronic -2,652,523,851.4 -588,113,129.0 -3,240,653,731.1 -16,750.7 Thermal 786,361.9 191,811.3 986,817.3 8,644.1 Total -8,106.5 Choline Chloride with Urea #6 & #2 Electronic -2,652,523,851.4 -588,113,129.0 -3,240,689,989.2 -53,008.8 Thermal 786,361.9 191,811.3 986,562.1 8,388.9 Total -44,619.9 Choline Chloride with Urea #6 & #3 Electronic -2,652,523,851.4 -588,113,129.0 -3,240,689,989.2 -53,008.8 Thermal 786,361.9 191,811.3 986,570.5 8,397.3 Total -44,611.6

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2.4 Results

Energies of formation have been calculated for five visually unique systems of choline chloridewithone urea molecule. The systems increase in stability in the

following order (as shown in Table III): position #2, position #1, position #6, position #3,

and position #5. Urea positions #3,#5, and#6have similar energies of formation. Based

on the figures inthis study (Figures 1-5), theurea in positions #1 and#2 arevisually closer to the OH portion ofcholinethantheother positions, which are visually closerto the chloride counterion. The remainingpositionshavemore opportunities for hydrogen bonding with both cholineand the counterion. Ureaposition#3 can form two NH Cl hydrogenbonds and an OH O=C hydrogenbond. Ureapositions#5 and #6 can

potentially form CH...O=C hydrogen bonds and NH Cl hydrogen bonds. The interaction with the OH portions of choline in positions #1 and #2 (OH OC andOH NH

respectively) are weaker than the sum of the interactions with the counterion andthe

remainder of choline in theremainingpositions.

Energies of formation have been calculated for seven visuallyunique systems of choline chloridewith two urea molecules. The systems increase in stability in the

following order (as shown in Table IV): urea #5 & #1, urea #6 & #1, urea #5 & #2, urea

#6 & #2, urea#3 & #1, urea#3 & #2, andurea #3 & #3. The most stable system, urea #3

& #3,has multiple points wheredoublehydrogen bonding can occur basedon visual inspectionof the figuresin this study (Figures 6-12). Two NH Cl hydrogenbonds can

occur betweenthe counterion and the closest urea. Two NH...O=C hydrogen bondscan

also occur between thetwoureamolecules. An OH...O=C hydrogenbond can also occur

between the second urea molecule and choline. These hydrogen bonds, thewaythe urea

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molecules areoriented, andtheinteractionbetweencholineand chloride, closely connect all of thecomponents of the system potentially leadingto it being themost stable.

This study was used as a springboard andreference for theremaining studies. The

optimized structures will be used to create inputs forthe remaining studies. The energies

of formation will be used as abase comparison point for theremaining studies.

Table III: Choline Chloride with OneUreaTotalEnergyof Formation Position Total Energyof Formation (J/mol)

Choline Chloride with Urea#2 -8,895.5

Choline Chloride withUrea#1 -27,161.7

Choline Chloride with Urea #6 -51,331.0

Choline Chloride with Urea #3 -52,112.8 Choline Chloride with Urea #5 -52,176.9

Table IV: Choline Chloride with TwoUrea Total Energyof Formation Position Total Energyof Formation (J/mol)

Choline Chloride with Urea #5 & #1 -7,252.0

Choline Chloride with Urea #6 &#1 -8,106.5

Choline Chloride with Urea #6 & #2 -44,619.9

Choline Chloride with Urea#3 & #2 -49,987.8 Choline Chloride withUrea#3 & #3 -62,35.8

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CHAPTER III

Gaussian Revision Comparison Study

After the Choline Chloride Study was completed, calculations performed within

the Gaussian software were moved tothe Ohio Supercomputer Center(OSC) to decrease processingtimes. Calculations were completed using Gaussian 09 Rev E.01 at OSC and

Gaussian 09 Rev D.01 and GaussView5.0.9on a local computer. Aquick comparison study was neededto verifythatthetworevisions provided thesame (or very similar)

results, removing thenecessity toregenerate all of the data generated on the local

computer.

Identical input files wereprocessed on a local computerand at OSC. Several

itemsfrom the output files were compared: convergence, electronic energy, thermal energy, frequency of vibrational mode #1, (Table V) andvisual output (examples in Figures 13-18).It was determined thatthe occasional, minor differences wouldnot significantlyimpactthe outcome of the studies ifdata from bothrevisionswereutilized.

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Table V: Local to OSC FrequencyandEnergy Comparison

Comparison

Number

Convergence ElectronicEnergy (hartrees) ThermalEnergy(kcaEmol) Frequencyof Vibrational Mode #1 (cm-1)

Local OSC Local OSC Local OSC Local OSC

1 Yes Yes -786.26964 -786.26964 140.081 140.081 63.41 63.41 2 Yes Yes -1010.29378 -1010.29378 188.348 188.347 36.02 36.00 3 Yes Yes -1234.31687 -1234.31687 236.464 236.464 22.88 22.88 4 Yes Yes -874.23347 -874.23347 236.566 236.565 17.76 17.79 5 Yes Yes -426.16387 -426.16387 139.912 139.912 43.34 43.34 6 Yes Yes -874.23682 -874.23682 236.680 236.680 15.50 15.50 7 Yes Yes -874.23347 -874.23347 236.566 236.565 17.76 17.79 8 Yes Yes -874.23848 -874.23848 236.844 236.844 24.26 24.26 9 Yes Yes -874.20557 -874.20557 235.846 235.846 12.99 12.99 10 Yes Yes -874.21907 -874.21907 235.659 235.659 21.42 21.42 11 Yes Yes -874.21907 -874.21907 235.660 235.660 21.33 21.33 12 Yes Yes -874.20612 -874.20612 235.771 235.771 8.95 8.95

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Figure 13: LocalComparison Number 1

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Figure 14: OSCComparison Number 1

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Figure 15: LocalComparison Number 2

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Figure 17: Local Comparison Number 12

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CHAPTER IV

Counterion Substitution Study 4.1 Procedure

Calculations forthe Counterion Substitution Studywere completed using

Gaussian 09 Rev E.01 at OSCand GaussView 5.0.9 on a local computer. This study was completed inthe same manner astheCholine Chloride Study, with the exception of how the initial input files werecreated.

To createthe input files, the chloride counterion wassubstituted with fluoride, hydroxide, and bromide counterions forthe most energetically probable Choline Chloride Study output systems, though these counterions arenottheonly possibilities. The Choline Chloride Study outputsutilizedwere the followingpositions: urea #3 & #1, urea #3 & #2,

urea#3 & #3, urea#5 &#1, urea#5 & #2, urea#6 & #1, and urea #6 & #2.

Optimizationand frequency calculations werecompleted for each system using

theHartree-Fock(HF)method andthe 6-31G(d,p) basis set. Each system was checked

for convergence, showingthat it has beensuccessfully optimized. Next, frequency values were verified to be positive, showing thatthe system has reached a local energy

minimum, nota saddle point.

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Once a system was confirmed to beoptimized and at a local energyminimum, the output file was reviewed for energydata. The electronic energy dataisprovided in hartrees and the thermal energy data is providedin kcal/mol. Both energy types were converted toJ/molpriortoperformingcalculations.

4.2 Fluoride Substitution

The first counterion substitution studied wasfluoride. This counterion was

selecteddue to fluorine being in thehalogen group on the periodic table with chlorine. It

was also selected to see whattheeffects ofa higher charge-densityion are on the DES

system.

Overallthe fluorideresults were visually similar to the chloride results (such as urea#5 & #2 in Figures 10 and 19), with the exceptionof urea#3 & #1 and urea #3 & #2

(Figures 6-7 and20-21).

The energies of formation were calculated inthe same mannerasthe Choline

Chloride Study, the sumof the reactantenergies wassubtracted from the sum of the product energies. The overall energies offormationof the fluoridesystems are much

more negative than the chloride systems, as showninthe differencecolumn in TableVI.

The same calculation and table format are used for the remaining counterion

substitutions. The fluoride systems’ energies of formation trend in the same orderasthe

chloridesystems, with the exception of urea#3 &#1 and urea #3 & #2, like thevisual results.

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Figure 19: Choline Fluoride with Urea #5 & #2

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Figure 20: Choline Fluoride with Urea#3 & #1

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Table VI: Choline Fluoride TotalEnergyof Formation Compared toCholine Chloride

Position TotalEnergyof Formation (J/mol)

Chloride Systems FluorideSystems Difference Urea #3 & #1 -100,207.8 -168,017.6 -67,809.8 Urea #3 & #2 -102,100.6 -159,703.3 -57,602.8 Urea #3 & #3 -114,148.6 -171,689.7 -57,541.2 Urea #5 & #1 -59,428.8 -89,460.2 -30,031.3 Urea #5 & #2 -93,978.8 -125,686.8 -31,708.0 Urea #6& #1 -59,437.5 -91,218.0 -31,780.5 Urea #6& #2 -95,950.9 -146,847.0 -50,896.1 4.3 Hydroxide Substitution

Thesecond counterion substitutionstudied was hydroxide. This counterion was

selectedto see whatthe effects of a simple diatomic counterion wouldbe on thesystem.

The hydroxide results followed the same trend asthefluoride results; remaining

visually similarto the chloride results (suchasurea#5 & #2 inFigures 10 and 22), with

the exception of urea #3 & #1 and urea#3 & #2 (Figures 6-7 and 23-24). Urea#3 & #1 and urea #3 & #2 ofthe hydroxide systemswerevisually similar to the fluoride systems.

The overallenergies of formation of thehydroxide systems are much more negative thanthe chloride systems, as shown in the difference column in TableVII,but not as negative asthe fluoride systems (Tables VI & VII). The hydroxide systems’

energies of formation trendin the same order as the chloride systems, with the exception of urea#3 & #1 andurea#3 & #2,like the visual results. The hydroxideanion has additionalcapacity tohydrogenbondduetothehydrogeninthe anion. Thoughitisnot readily seen in these calculationsit may playa role in a full analysis similar tothe

Choline Chloride Study.

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Figure 22: Choline Hydroxide withUrea#5 & #2

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Table VII: Choline Hydroxide Total Energyof Formation Compared to Choline

Chloride

Position Total Energyof Formation (J/mol)

Chloride Systems Hydroxide Systems Difference Urea #3 & #1 -100,207.8 -150,102.5 -49,894.7 Urea #3 & #2 -102,100.6 -156,921.5 -54,821.0 Urea #3 & #3 -114,148.6 -150,393.5 -36,244.9 Urea #5 & #1 -59,428.8 -83,419.5 -23,990.7 Urea #5 & #2 -93,978.8 -118,556.6 -24,577.8 Urea #6& #1 -59,437.5 -84,049.1 -24,611.6 Urea #6& #2 -95,950.9 -136,952.5 -41,001.6 4.4 Bromide Substitution

The third counterion substitution studied was bromide. This counterion was

selectedto determine if there is an energy of formation trend withinthehalogen group of

the periodic table. When reviewingfluoride and chloride it follows thatthe energies of formation are increasingly negative when moving from less to moreelectron-denseions with the halogen group. The bromidedata with either support or contradict the potential trend.

The bromide results were visually similartothe chloride results for all systems

(such as urea#5 & #2 and urea #3 & #1 in Figures 10, 6, and 25-26). The bromide system didnot see large deviations like fluorideand hydroxidesystems.

The overallenergies of formation of thebromide systems are slightly more

negative thanthe chloride systems, as shown in the difference column in TableVIII. The

potentialenergies of formation trend for the halogen group didnot hold true. Ifthe trend held, the bromide energies of formation would beless negative thatthe chloride systems. The bromide systems’ energies of formation trend in the same orderasthe chloride systems, with the exception of urea #3 & #1 andurea#3 & #2, unlikethe visual results.

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Figure 25: Choline Bromide with Urea#5 & #2

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Figure 26: Choline Bromide with Urea#3 & #1

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Table VIII: Choline Bromide Total EnergyofFormation Compared to Choline Chloride

Position Total Energyof Formation (J/mol)

Chloride Systems Bromide Systems Difference Urea #3 & #1 -100,207.8 -111,653.0 -11,445.2 Urea #3 & #2 -102,100.6 -111,598.2 -9,497.6 Urea #3 & #3 -114,148.6 -123,098.2 -8,949.6 Urea #5 & #1 -59,428.8 -64,719.5 -5,290.6 Urea #5 & #2 -93,978.8 -97,851.7 -3,872.9 Urea #6& #1 -59,437.5 -64,884.5 -5,447.0 Urea #6& #2 -95,950.9 -106,307.7 -10,356.8 4.5 Results

This study wascompleted as a quick wayto determine possibletrends and determine which system should have afull analysis completed, similar totheCholine

Chloride Study. In addition, theeffects ofelectron-density of the counterion were observed on both the choline salts and thecholine salt systems with twourea molecules.

Visually there is a difference in the distance(in angstroms)betweenthe

counterion andthe closesthydrogen on thenearest urea, which can easily be seenis Figures 10, 19, 22, and 25. Bond lengths were reviewed for urea#3 & #3,urea #5 & #1,

urea#5 & #2, urea#6 &#1, and urea #6& #2, shown in Table IX.

For each set of urea positions, the distancebetweenthe atoms inquestion

increases as the electron-densitydecreases,fluoride, hydroxide, chloride, and bromide

respectively. This corresponds to a decrease instrengthof hydrogenbonding, inthe same

order.

As a result of this observation, the distances(in angstroms)betweensome atoms

in the optimized choline salt structures werealso reviewed to determine if the

electron-density of the counterion affects the shape of the cholinesalt. The bonddistances

between the counterion and nitrogen ofcholine,atoms 22and 13 (notethat atom 13 is

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behind atoms 5 and 8) respectively, in Figure 27 were reviewed. Alsoreferringto Figure

27, the distance between hydrogens 7 and 20, 12 and 7, and 8 and4 were reviewed. Table

X shows the distances between these atoms.

As electron densityof the counterion increases, the distance between the

counterion and nitrogen decreases. This shows thatthe more electron-dense counterions arecloserto choline, causing a stronger interaction between the counterion and the choline cation. Aselectron density of the counterion increases, the distances between the

hydrogens 7 and 20 decrease, the distancesbetweenhydrogens 12 and 7 decrease, andthe distancesbetweenhydrogens 8 and4 increase. Thesedistances show thatthehydrogen

atomsclosest to the counterion are more strongly drawntothe counterions with higher electron-density. The more electron-dense thecounterion, the more the choline cation is deformed toward the counterion.

Throughout the substitution study, urea#3 & #1 andurea#3 & #2have shown somevariancevisually and in theenergyof formation trends. Using the chloride systems

as abase, the more electron-dense counterionsshow alterations in the visualstructure,

drawinga urea molecule awayfrom theOH of the choline cation and more closely to the

counterion. The bromide systemdidnot showthe same visual discrepancy, though there was a discrepancy in the energy of formation trend. Inthe bromide system, the urea that

can interact with boththe counterion and theOH portion of thecholine cation has a

stronger OH O=C hydrogen bonding interactiondepictedbytheshorterbond lengthin

Table XI, whichcould account for the difference inthe energy of formation.

Overall, the fluoride systems hadthemost negative energies of formation of all systems reviewed inthis study (TableXII). This is indicative of the greater counterion to

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choline cation interactionandthe stronger hydrogen bonding interactionsalready discussed. The fluoride systems alsohad the greatest deviations fromthe basechloride systems(Table XIII). Due to these findings, cholinefluoride was selectedto go through a fullanalysis in a similar fashion tothe Choline Chloride Study.

Table IX: Counterion Substitution StudyBondLength Comparison

Urea Numbers Counterion Distance: Counterion toH of Urea(A)

3 3 Fluoride 1.80336 Hydroxide 1.88531 Chloride 2.46339 Bromide 2.59213 5 1 Fluoride 1.60681 Hydroxide 1.68826 Chloride 2.41794 Bromide 2.5728 5 2 Fluoride 1.51634 Hydroxide 1.53471 Chloride 2.30518 Bromide 2.47372 6 1 Fluoride 1.57125 Hydroxide 1.6441 Chloride 2.38774 Bromide 2.55316 6 2 Fluoride 1.65958 Hydroxide 1.72438 Chloride 2.42449 Bromide 2.56873 49

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Figure 27: CholineSaltAtom Numbering

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Table X: Distance Between Atoms inCholine Salts

Counterion

Distance betweenatoms (A) Counterion 22 Nitrogen 13 Hydrogen 7 Hydrogen20 Hydrogen 12 Hydrogen7 Hydrogen8 Hydrogen 4 Fluoride 2.88751 2.39406 2.24365 2.44668 Hydroxide 2.95309 2.50102 2.26995 2.43866 Chloride 3.64327 2.64527 2.38326 2.42801 Bromide 3.76016 2.70324 2.38280 2.42854

Table XI: Lengthof C=O HO Hydrogen Bond

Urea Numbers Counterion Fengthof C=O...HO HydrogenBond (A)

3 1 Chloride 2.13207

Bromide 2.09241

3 2 Chloride 3.11131

Bromide 2.27780

Table XII: Counterion Substitution StudyTotal Energyof Formation

Position

Total EnergyofFormation (J/mol) Chloride Systems Fluoride Systems Hydroxide Systems Bromide Systems Urea #3 &#1 -100,207.8 -168,017.6 -150,102.5 -111,653.0 Urea #3 & #2 -102,100.6 -159,703.3 -156,921.5 -111,598.2 Urea #3 & #3 -114,148.6 -171,689.7 -150,393.5 -123,098.2 Urea #5 &#1 -59,428.8 -89,460.2 -83,419.5 -64,719.5 Urea #5 & #2 -93,978.8 -125,686.8 -118,556.6 -97,851.7 Urea #6 &#1 -59,437.5 -91,218.0 -84,049.1 -64,884.5 Urea #6&#2 -95,950.9 -146,847.0 -136,952.5 -106,307.7 51

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TableXIII: Counterion Substitution Study Total Energyof Formation Difference

Position

Difference in TotalEnergyof Formation Compared to Chloride Systems (J/mol)

Fluoride Systems Hydroxide Systems BromideSystems Urea #3 & #1 -67,809.8 -49,894.7 -11,445.2 Urea #3 & #2 -57,602.8 -54,821.0 -9,497.6 Urea #3 & #3 -57,541.2 -36,244.9 -8,949.6 Urea #5 & #1 -30,031.3 -23,990.7 -5,290.6 Urea #5 & #2 -31,708.0 -24,577.8 -3,872.9 Urea #6& #1 -31,780.5 -24,611.6 -5,447.0 Urea #6& #2 -50,896.1 -41,001.6 -10,356.8 52

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CHAPTER V

Choline Fluoride Study 5.1 Procedure

Calculations were completed fortheCholine Fluoride Study usingGaussian09

Rev E.01 at OSCandGaussView5.0.9 on a localcomputer. This study was completed in the same manner as the Choline Chloride Study,including how the input files were

created.

Optimizationand frequency calculations werecompleted for each system using

theHartree-Fock(HF)method andthe 6-31G(d,p) basisset. Each system waschecked for convergence, showingthat it has beensuccessfully optimized. Next, frequency values were verified to be positive, showing thatthe system has reached a local energy

minimum, nota saddlepoint.

Once a system was confirmed to beoptimized and at a local energyminimum, the output file was reviewed for energydata. The electronic energy dataisprovided in hartrees and the thermal energy data is providedin kcal/mol. Both energy types were converted toJ/molpriortoperformingcalculations.

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5.2 Choline Fluoride with One Urea Molecule

Optimizationand energy calculations were completed forcholine fluoride and urea separately in previous studies. The optimized urea molecule was placed in six

locations aroundthe optimized choline fluoride molecule, resulting infivevisually unique optimized structures (Figures 28-32). These six locationswerethe same general location and orientationsastheureamolecules in thecholine chloride with one urea

moleculeportionof the Choline Chloride Study. The fluoride systems didnot mimic urea

#7 from the Choline Chloride Studydueto the input being too structurallysimilarto urea #6.

Thoughthe input positions weresimilar, theoutputpositions varied slightly

visually for positions #1 and #4. In position #1 (Figures 1 and 28), theurea molecule

remained in thesame generallocation, but is drawn more closelytothecholine cation in the fluoride system. Position #4 of thefluoride system (Figure 31) is compared to

position #5 of the chloride system(Figure 4), dueto the similar visual andenergyof

formation results forpositions #4 and#5 inthe chloride system. Inthe fluoride system

position #4, the urea molecule remaininginthe same general location, butis drawn more closely to the counterion in thefluoride system.

Thoughthe input positions were similar, the outputpositions variedgreatly visually for positions #2, #3, and #6. In position #2 (Figures 2 and 29), the urea molecule was located aroundthe OHportionofcholine chloride but moved to the counterion in the fluoride system. This changesthe hydrogen bonding opportunity from OH NH inthe

chloride systemto NH F in the fluoride system. In position#3 (Figures 3 and 30), the ureamolecule wasable to interact with boththe counterion andOH inthe chloride

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system (NH...Cl andOH...O=C). Inthe fluoride system (position #3) theureamolecule only has the ability to interact with theOH portion of thecholine cation which wouldbe

expected to showa decrease in energy for formationduetothereducedability for

hydrogen bonding. In position #6 (Figures 5 and 32), theureamoleculewas located

aroundthe counterion inthe chloride systembut moved to theOHportionof choline fluoride. Thischangesthe hydrogen bondingopportunityfrom NH...Cl inthechloride

system to OH NH and addingCH...O=C.

The electronic andthermal energies, from the Gaussian results, were usedto calculatethe overall energy of formation (Table XIV). Table XIV is set up as areaction, showing that Xreactant plus Yreactantyields aproduct. The energies for each

component (fromtheoutput files) of the reaction are shown in line, vertically with the

component. To calculate theenergy of formation the sumof the reactant energies was subtractedfrom the sumof the product energies.

The twourea positions that resulted in visually similarresults, positions #4and

#5, were also considered to be numerically equivalent. As a result, of these two positions,

only position#4 is considered inthenext set ofsystemsto bereviewed.

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Figure 28: Choline Fluoride with Urea#1

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Figure 30: Choline Fluoride with Urea #3

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Table XIV: Choline Fluoride with One Urea Energyof Formation Calculations Position Energy Type CholineFluoride Energy (J/mol) + Urea Energy (J/mol) →

Choline Fluoride Urea

Energy (J/mol)

Energyof

Formation (J/mol) CholineFluoride with

Urea #1

Electronic -1,118,893,240.7 -588,113,129.0 -1,707,038,085.7 -31,716.0

Thermal 585,391.8 191,811.3 785,784.5 8,581.4

Total -23,134.7

CholineFluoride with

Urea#2

Electronic -1,118,893,240.7 -588,113,129.0 -1,707,118,268.5 -111,898.8

Thermal 585,391.8 191,811.3 789,579.4 12,376.3

Total -99,522.5

CholineFluoride with Urea #3

Electronic -1,118,893,240.7 -588,113,129.0 -1,707,047,274.9 -40,905.3

Thermal 585,391.8 191,811.3 786,374.4 9,171.3

Total -31,734.0

Urea #4

Electronic -1,118,893,240.7 -588,113,129.0 -1,707,096,713.1 -90,343.5

Thermal 585,391.8 191,811.3 786,286.6 9,083.5

Total -81,260.0

Urea #5

Electronic -1,118,893,240.7 -588,113,129.0 -1,707,096,713.1 -90,343.5

Thermal 585,391.8 191,811.3 786,274.0 9,070.9

Total -81,272.5

CholineFluoride with Urea #6

Electronic -1,118,893,240.7 -588,113,129.0 -1,707,038,085.7 -31,716.0

Thermal 585,391.8 191,811.3 785,780.3 8,577.2

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5.3 Choline Fluoride with Two Urea Molecules

The twomostexothermicresults from Table XIVwere selected for the nextset of calculations,urea positions #2 and #4. An additional optimized urea molecule was added

to three locations ofeachof the selectedcholine chloride urea systems. Optimization and energy calculations were completed for the new systems. Ureapositions#2 and#4 each resulted inthree visually unique results (Figures 33-38).

The electronic andthermal energies, from the Gaussian results, were usedto calculatethe overall energy of formation (Table XV). Table XV is set up inthe same

manneras Table XΓV

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Table XV: Choline Fluoride with Two UreaEnergyof Formation Calculations

Position Energy

Type

Choline FluorideUrea

Energy (J/mol) +

Urea

Energy (J/mol) →

Choline Fluoride 2 Urea Energy (J/mol) Energy of Formation (J/mol) CholineFluoride with Urea #2 & #1 Electronic -1,707,118,268.5 -588,113,129.0 -2,295,308,770.9 -77,373.5 Thermal 789,579.4 191,811.3 990,281.7 8,891.0 Total -68,482.5 CholineFluoride with Urea #2& #2 Electronic -1,707,118,268.5 -588,113,129.0 -2,295,249,592.1 -18,194.7 Thermal 789,579.4 191,811.3 990,306.8 8,916.1 Total -9,278.6 CholineFluoride with Urea #2 & #3 Electronic -1,707,118,268.5 -588,113,129.0 -2,295,309,611.1 -78,213.6 Thermal 789,579.4 191,811.3 992,239.8 10,849.1 Total -67,364.5 CholineFluoride with Urea #4&#1 Electronic -1,707,096,713.1 -588,113,129.0 -2,295,226,172.7 -16,330.6 Thermal 786,286.6 191,811.3 986,214.8 8,117.0 Total -8,213.7 CholineFluoride with Urea #4&#2 Electronic -1,707,096,713.1 -588,113,129.0 -2,295,229,480.8 -19,638.7 Thermal 786,286.6 191,811.3 986,708.5 8,610.7 Total -11,028.1 CholineFluoride with Urea #4&#3 Electronic -1,707,096,713.1 -588,113,129.0 -2,295,262,168.3 -52,326.2 Thermal 786,286.6 191,811.3 985,993.1 7,895.2 Total -44,431.0

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5.4 Results

Energies of formation have been calculated for five visually unique systems of choline fluoridewithoneureamolecule. The systems increase in stabilityinthe

following order (asshown in Table XVI): position #1, position #6, position #3, position

#4, and position #2. Referτing to Figures 28-32,positions #1 and #6have visually similar structures which have ability tohydrogen bond, butthe interactions may be strained due

totheposition.Position#3 was noted earlierto have moved to avisually less stable

structure, which was verified in the energyof formationcalculations. The total energyof

formation of position #3 in thechloride system was -52,112.8 J/mol (Table I) and -31,734.0J/mol in the fluoride system (TableXIV). Positions #4 and#2 have

opportunities fordoublehydrogen bonding. In position #4, anF HN hydrogen bond can occur as wellas two CH...O=C hydrogen bonds. Inposition #2, two NH Fbonds can occur. The sumof the strength of interactions in positions #2 and#4 are greater than the interactions in the otherpositions.

Energies of formation have been calculated for six visuallyunique systems of choline fluoridewithtwoureamolecules. The systemsincrease in stability in the

following order (as shown in Table XVII): urea#4 & #1, urea#2 & #2, urea#4 & #2,

urea #4 & #3, urea#2 & #3, and urea #2 & #1. Basedon visual inspectionof Figures 33-38, the additional urea in urea #2 & #3 mirrorsthe initial urea about the counterion. Two ureamoleculeshavethe ability to create two NH F hydrogenbonds, creating a stable system. Urea#2 & #1 is the combination ofoneurea system positions #4 and #2, the two positions selected for further analysis. These two interactionswere the strongest

individually, combining toprovidethemost stable system.

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Table XVI: Choline Fluoride with OneUrea TotalEnergyof Formation Position Total EnergyofFormation (J/mol)

Choline Fluoride with Urea#1 -23,134.7

Choline Fluoride withUrea#6 -23,138.8

Choline Fluoride with Urea #3 -31,734.0

Table XVII: Choline Fluoridewith Two Urea TotalEnergyof Formation Position Total Energyof Formation (J/mol)

Choline Fluoride withUrea #4 &#1 -8,213.7

Choline Fluoride with Urea #2 & #2 -9,278.6

Choline Fluoride with Urea #4 & #2 -11,028.1 Choline Fluoride with Urea #4 & #3 -44,431.0

Choline Fluoride with Urea#2 & #3 -67,364.5

Choline Fluoride with Urea #2 &#1 -68,482.5

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CHAPTER VI

Conclusion

Davies andAbbott (2) showthatthe freezing point depression of choline salts and urea changes with the counterion ofcholine. Pureurea has ameltingpoint of 406 K. The

addition ofacholine salt decreasesthe freezing point inthe following orderby

counterion, fluoride (274 K), nitrate (277 K), chloride (285 K), and tetrafluoroborate (340

K), with fluoride exhibitingthe greatest freezing pointdepression and tetrafluoroborate exhibiting the least(2). The data fromthe Choline Chloride StudyandtheCholine Fluoride Study showsthatthe fluoride systems have a greater strengthofinteractionthan the chloride systems. This data coupled with the freezing point information from the Davies and Abbott study, supportsthe hypothesis thatthe system with the greater

theoretical strength of interaction, will havemore non-ideal physical properties.

Ashworth et al. (5), Davies andAbbott (2), Hammond etal. (11), andmanyother studiesdiscuss hydrogen bonding and bondstrength with respect to the reline structure. The Counterion Substitution Study shows the effectsof counterion electron-density on hydrogen bonding visually and numerically within eachsystem. The number and strength of hydrogen bonds affectsthe overall structureof thecholine salt andthepositioningof the urea molecules. The Choline Chloride Studyandthe CholineFluoride Studynotethat

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many types of hydrogen bondsthatcan occur withinthe choline salt andurea systems. Ashworth et al. (5) notes thatthe followingtypes of neutral, ionic, ordoubly ionic

hydrogenbonds arepossible with eachtype varying instrength depending on thespecific

system itis in: OH...O=C, NH...O=C, OH...Cl (or other counterion), NH...Cl (or other

counterion), OH...NH, CH...Cl (or other counterion), CH...O=C, NH...OH, andNH...NH.

For thisreason, it is difficult to use thenumberof hydrogen bond opportunitiesas aguide

for the stability ofthe system.

Based on thetrends noted andthetunabilityof DESs, it is reasonable to expect

the systems studiedto have melting points increasing inthe following order: fluoride, hydroxide, chloride, andbromide. More theoreticaland physical research is needed to

verifythe interactions and properties of the hydroxide and bromide systems. The

theoreticalresearch needed isthe analysis of hydroxide andbromide, in a similarfashion tothe studiescompleted forchloride and fluoride, inthis research. Physical testing data for melting pointare neededfor the hydroxide and bromide systems as a point of

comparison.

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