ORGANIC CHEMISTRY

Organic

Organic

Chemistry

Chemistry

Presented by

Presented by

GL Kapde

GL Kapde

Presented by

Presented by

GL Kapde

GL Kapde

Introductions

Introductions

1.

1. Or

Orga

ganic c

nic che

hemic

micals

als com

compo

poun

unds a

ds app

ppear i

ear in

n

materials like clothing, fuels, polymers

materials like clothing, fuels, polymers

dyes and medicines.

dyes and medicines.

2.

2. F

F. W

. Wohle

ohler synt

r synthesi

hesised an o

sed an org

rganic

anic

compound, urea from an inorganic

compound, urea from an inorganic

compound, ammonium cyanate.

compound, ammonium cyanate.

STRUCTURAL

REPRESETATIO O!

ORGAIC CO"POU#S

Complete, condensed and bond line structural formulas

_{Organic compounds structures are}

represented in several ways.

1. The Lewis structure or dot structure, dash structure, condensed structure and

bond line structural formulas are some of the specic types.

2. The !ewis structures, however, can be simplied

by representing the two"electron covalent

 Thus, ethane #&2'(%, ethene #&2')%, ethyne #&2'2%

*uch structural representations are called complete structural formula

' ' ' & & ' ' '   +thane ' ' & & ' '   _+thene ' & & '   +thyne

 These structures can also be represented by the following ways

&' &' '2& '2& '& '&

+thane +thene +thyne

organic chemists use another way of representing the structures, in which only lines are used. -n this bond"line structural representation of organic

compounds, carbon and hydrogen atoms are not shown and the lines representing carbon"carbon bonds are drawn in a ig"ag fashion.

For e/ample

i% &'&'2&'&'2&'2&'2&'2&'

0

"ethyloctane can be represented in various

Three$#imensiona%

Representation o& Organic

"o%ecu%es

 The three"dimensional #"3% structure of organic molecules can be represented on paper by using certain conventions. For

e/ample, by using solid and dashed

wedge formula, the "3 image of a molecule from a two"dimensional picture can be

perceived._{solid"wedge is used to indicate a bond} pro4ecting out of the plane of paper, towards the observer.

  5   5   5   5   5   5   5   5   5   5   5   5   5   5   5   5   5   5   5   5   5   5   5   5   5   5   5   5   5   5   5   5   5   5   5   5   5   5   5   5   5   5   5   5   5   5   5   5   5   5   5   5   5   5   5   5   5   5   5

 The dashed"wedge is used to depict the bond pro4ecting out of the plane of the paper and away from the observer.

 The bonds lying in plane of the paper are depicted by using a normal line #6%.

Wedge-and-dash representation of CH4

&!7**-F-&7T-O8 OF O9:78-&

&O;O<83*

 Acyclic or open chain

compounds

 These compounds are also called as a%iphatic compounds and consist of straight or branched chain compounds, for e/ample

 Alicyclic or closed chain or ring

compounds

7licyclic #aliphatic cyclic% compounds contain carbon atoms 4oined in the form of a ring

#homocyclic%. *ometimes atoms other than

carbon are also present in the ring #heterocylic%. *ome e/amples are

 Aromatic compounds

7romatic compounds are special types of compounds.

 These include benene and other related ring compounds #benenoid%.

-n order to clearly identify compound, a systematic method of naming has been developed and is known as the IUPAC

'Internationa% Union o& Pure and App%ied Chemistry( system o& nomenc%ature)

 The names are correlated with the structure

such that the reader or listener can deduce the structure from the name.

 The traditional names are considered a trivial or common names.

*ydrocarbons +

*ydrocarbons +

&ompounds containing carbon&ompounds containing carbon and

Straight chain hydrocarbons:

Straight chain hydrocarbons: The names of su The names of suchch compounds are based on their chain structure, and compounds are based on their chain structure, and end with su=/ >"

end with su=/ >"ane’ and carryane’ and carry a pre/ indicatinga pre/ indicating the number of carbon atoms present in the chain the number of carbon atoms present in the chain #e/cept from &') to &)'1?, where the pre/es are #e/cept from &') to &)'1?, where the pre/es are derived from trivial names%.

Branched chain hydrocarbons:

-n a

branched chain compound small chains of carbon atoms are attached at one or more carbon atoms of the parent chain. The small carbon chains

#branches% are called alkyl groups.

-n order to name such compounds, the names of alkyl groups are pre/ed to the name of parent

alkane. 7n alkyl group is derived from a saturated hydrocarbon by removing a

hydrogen atom from carbon. Thus, &') becomes "&' and is called methyl group.

Nomenclature of branched

chain alkanes

1

.

 First of all, the %ongest carbon chain in the mo%ecu%e is identi,ed)_+/ampl

- ) The numbering is done in such a .ay that the branched carbon atoms get the %o.est possib%e numbers)

. -f di@erent alkyl groups are present, they are listed in alphabetical order. Thus, name for the compound shown above is ("ethyl"2" methylnonane.

A8ote the numbers are separated from the groups by hyphens and there is no break between methyl and nonane.B

). -f two or more identical substituent groups are present then the numbers are separated by

commas. The names of identical substituents are not repeated, instead pre/es such as di #for 2%, tri #for %, tetra #for )%, penta #for C%, he/a #for (% etc. are used.

C. -f the two substituents are found in eDuivalent

positions, the %o.er number is gi/en to the one coming ,rst in the a%phabetica% %isting)

(. The branched alkyl groups can be named by

following the above mentioned procedures. carbon atom o&the branch that attaches to the root a%0ane is numbered 1 as e2emp%i,ed below.

While writing the trivial names of substituentsE in a%phabetica% order3 the pre,2es iso$ and neo$ are considered to be the part o& the

&undamenta% name o& a%0y% group) The

pre,2es sec- and tert- are not considered to be the part of the fundamental name._{-n multi"substituted compounds, the following}

rules may also be remembered

 -f there happens to be two chains of eDual sie, then that chain is to be selected which contains more number of side chains.

 7fter selection of the chain, numbering is to be done from the end closer to the

For e/ample

Cyclic Compounds: A saturated

monocyclic :

&

ompound is named by pre/ing >cyclo’ to the corresponding straight chain alkane. -f side chains are present, then the rules given above are applied. 8ames of some cyclic compounds

 _{7 functional group, as dened earlier, is an atom}

or a group of atoms bonded together in a uniDue manner which is usually the site of chemical

reactivity in an organic molecule.

_{For e/ample, &'O', &'&'2O', and}

#&'%2&'O' 6 all

having "O' functional group liberate hydrogen on reaction with sodium metal.

_{First of all, the functional group present in the}

molecule is identied which determines the choice of appropriate su=/.

The %ongest chain o& carbon atoms

containing the &unctiona% group is numbered in such a .ay that the &unctiona% group is

attached at the carbon atom possessing %o.est possib%e number in the chain)

_{-n the case of poly functional compounds, one of}

the functional groups is chosen as the principal

functional group and the compound is then named on that basis.

 _{The choice of principal functional group is made}

on the basis

of order of preference. The order o& decreasing priority &or some &unctiona% groups is+

$COO*3 4SO5*3 $COOR 'R6a%0y% group(3 COC%3 $CO*-3 $C3$*C6O3 7C6O3 $O*3 $*-3

For -<;7& nomenclature of substituted benene compounds, the substituent is placed as pre/ to the word benene as shown in the following

-f benene ring is disubstituted, the position of substituents is dened by numbering the carbon atoms of the ring such that the substituents are located at the lowest numbers possible.

-n the trivial system of nomenclature the terms ortho !o", meta !m" and para !p" are used as

pre/es to indicate the relative positions 1,2" G1," and 1,)" respectively.

 

Structura%

Isomerism

(i 

 )

Chain isomerism

: When two or more compounds have similar molecular formula but

di@erent carbon skeletons, these are referred to as chain isomers and the phenomenon is

(ii) Position isomerism:

When two or more

compounds di@er in the position of substituent atom or functional group on the carbon skeleton, they are called position isomers and this phenomenon is

termed as position isomerism.

(iii) unctional group isomerism:

 Two or

more compounds having the same molecular formula but di@erent functional groups are called functional isomers and this phenomenon is termed as functional group isomerism.

(i!) "etamerism:

-t arises due to di@erent alkyl chains on either side of the functional group in the molecule.

Stereoisom

erism

 The compounds that have the same

constitution and seDuence of covalent

bonds but di@er in relative positions of

their atoms or groups in space are

called stereoisomers

.

 This special type

of isomerism is called as

stereoisomerism and can be classied

as

geometrical and optical isomerism

.

-n an organic reaction, the organic molecule #also referred as a substrate% reacts with an

appropriate attacking reagent and leads to the formation of one or more intermediate#s% and nally product#s%

 _{*ubstrate is that reactant which supplies carbon}

to the new bond and the other reactant is called reagent.

_{-f both the reactants supply carbon to the new}

bond then choice is arbitrary and in that case the molecule on

which attention is focused is called

_{Reaction mechanism+}

_{7 seDuential}

subst rate.

account of each step, describing details of

electron movement,

energetics during bond cleavage and

bond

formation, and the rates of transformation

of reactants into products #kinetics% is

!ission o& a Co/a%ent

:ond

C%ea/ages o& co/a%ent bonds 'i( *etero%ytic c%ea/age+ -n

hetero%ytic clea!age# the bond breaks in such a fashion that the shared pair of electrons remains with one of the fragments.

()_{one atom has a se/tet electronic}

structure and a positive charge and the other, a valence octet with at least one lone pair and a negative charge.

'ii( *omo%ytic c%ea/age+ -n homolytic clea!age# one of the

electrons of the shared pair in a covalent bond goes with each of the bonded atoms. Thus in homolytic cleavage, the movement of a single electron takes place instead of an electron pair.

 _{7 species having a carbon atom possessing}

se/te/t of electrons and a positive charge is called a carbocation !earlier called carbonium ion".

 _{The observed order of carbocation stability is}  _{The organic reactions which proceed through}

heterolytic bond cleavage are called ionic or heteropo%ar or ;ust po%ar

 _{*uch cleavage results in the formation of}

neutral species #atom or group% which contains an unpaired electron. These species are called free radicals.

 _{7 homolytic cleavage can be shown as}

 _{Organic reactions, which proceed by}

homolytic ssion are called free radical or homopolar or nonpolar reactions.

uc%eophi%es and

E%ectrophi%es

uc%eophi%e #8u%

+

7 reagent that brings an electron pair i.e., nucleus seeking and the

reaction is then called nuc%eophi%ic)

E%ectrophi%e 'E<(+ 7 reagent that takes away an electron pair i.e., electron seeking and the reaction is called e%ectrophi%ic)

 _{3uring a polar organic reaction, a nucleophile}

attacks an electrophilic centre of the substrate which is that specic atom or part of the

electrophile that is electron decient.

_{*imilarly, the electrophiles attack at nucleophilic}

E%ectron "o/ement in Organic

Reactions

 The movement of electrons in organic reactions can be shown by curved"arrow notation.

;resentation of shifting of electron pair is given below 

 _{ovement of single electron is indicated by a}

single barbed >sh hooksE #i.e. half headed curved arrow%.

E%ectron #isp%acement E=ects in

Co/a%ent :onds

 The electron displacement in an organic molecule may take place either in the ground state under the inHuence of an atom or a substituent group or in the presence of an appropriate attacking reagent.

e/amples of this type of electron displacements are

• resonance e@ects • -nductive e@ect

Resonance Structure+ 7 single !ewis structure cannot e/plain all the property of the molecule hence many !ewis structure are proposed for a

some molecule to e/plain the properties. 3i@erent !ewis structure proposed are called as resonance !ewis structure or canonical form of contributing structure the phenomenon is called resonance

and the structures proposed are called resonance structure.

 _{The resonance structures #canonical structures}

or contributing structures% are hypothetical and individually do not represent any real molecule._{structure and the lowest energy resonance} The di@erence in energy between the actual

structure is called the resonance stabilisation energy or simply the resonance energy$

 The following rules are applied while writing resonance structures

 The resonance structures have #i% the same positions of nuclei

#ii% the same number of unpaired electrons. Resonance E=ect+ The resonance e@ect is

dened as >the polarity produced in the molecule by the interaction

of two I"bonds or between a I"bond and lone pair of electrons present on an ad4acent atomE.

 There are two types of resonance e@ect

#i% ;ositive 9esonance +@ect #J9 e@ect%

 : -n this e@ect, the transfer of electrons is away

from an atom or substituent group attached to the con4ugated system.

#ii%

8egative 9esonance +@ect #" 9 e@ect%

 This e@ect is observed when the transfer of

electrons is towards the atom or substituent group attached to the con4ugated system.

Inducti/e E=ect+

 The process of electron displacement of electrons along the chain of carbon atoms due o the presence

of a polar covalent bond at one end of the chain.  This is a permanent e@ect and is generally

E%ectromeric E=ect 'E

e=ect(

-t is dened as the complete transfer of a shared pair of I"electrons to one of the atoms 4oined by a multiple bond on the demand of an attacking

reagent.

-t may be noted that this e@ect decreases sharply as we move away from the atom involved in the initial polar bond and becomes negligible from the fourth atom onwards.

-t arises whenever an electron withdrawing group is attached to end of a carbon chain.

 _{There are two distinct types of electromeric}

e@ect.

#i% ;ositive +elctromeric +@ect #J+ e@ect%

-n this effect the IKelectrons of the multiple bond are transferred to that atom to which the reagent gets attached. For e/ample 

#ii% 8egative +lectromeric +@ect #$ + e@ect%

-n this effect the I " electrons of the multiple bond are transferred to that atom to which the attacking

*ypercon;ugatio

n

'ypercon4ugation is a general stabilising interaction. -t involves delocalisation of L electrons of &6' bond of an alkyl group directly attached to an atom of

unsaturated system or to an atom with an unshared p orbital. 'ypercon4ugation is a permanent e@ect.

Once an organic compound is e/tracted from a

natural source or synthesised in the laboratory, it is essential to purify it. Marious methods used for the purication of organic compounds are based on the nature of the compound and the impurity present in it.

"ET*O#S O! PURI!ICATIO O!

ORGAIC CO"POU#S

 The common techniDues used for purication are as follows 



 Sub%imation

+ -n this process the solid substance changes from solid to vapour form without going to the liDuid state it is used to separate sublimable compound from non" sublimable impurities.



 Crysta%%isation

+ -t is based on the di@erence in

the solubilities of the compound and the impurities in a suitable solvent

.



 #isti%%ation

+ This important method is used to separate"

#i%

Molatile liDuids from nonvolatile impurities

#ii%

7nd the liDuids having su=cient di@erence in their boiling points.

3istillation is further divided in to 

i% Fractional distillation -f the di@erence in boiling points of two

liDuids is not much, simple distillation cannot be used to separate them. The techniDue of fractional

distillation is used in such cases.

ii% *team distillation  This techniDue is applied to

separate substances which are steam volatile and are immiscible with water.



#i=erentia% E2traction+

 The organic solvent and

the aDueous solution should be immiscible with each other so that they form two distinct layers which can be separated by separatory funnel.



  Chromatography+

-n this techniDue, the mi/ture of substances is applied onto a stationary phase, which may be a solid or a liDuid. 7 pure

solvent, a mi/ture of solvents,

or a gas is allowed to move slowly over the stationary phase.

C*RO"ATOGRAP *> 

7dsorption chromatography 

-s based on the

fact that di@erent compounds are adsorbed on an adsorbent to di@erent degrees.

 _{&ommonly used adsorbents are silica gel and}

&olumn chromatography -t

involves

separation of a mi/ture over a column of adsorbent #stationary phase% packed in a glass tube.

 Thin layer chromatography #T!&%

-s another type of adsorption chromatography, which

involves separation of substances of a mi/ture over a thin layer of an adsorbent coated on glass plate.

;artition

chromatograph

y

&ontinuous di@erential partitioning of component of a mi/ture between stationary and

mobile phase.

 The relative adsorption of each component of the mi/ture is e/pressed in terms of its retardation &actor)

?UALITATI@E

AAL>SIS O!

ORGAIC

CO"POU#S

 The elements present in organic compounds are carbon and hydrogen. -n addition to these, they may also contain o/ygen, nitrogen, sulphur,

halogens and phosphorus.

#etection o& Carbon and *ydrogen

&arbon and hydrogen are detected by heating the compound with copper#--% o/ide.

&arbon present in the compound is o/idised to carbon dio/ide #tested with lime"water, which develops turbidity%

'ydrogen to water #tested with anhydrous copper sulphate, which turns blue%.

#etection o& Other E%ements+

8itrogen, sulphur, halogens and phosphorus present in an organic compound are detected

by LassaigneBs test)

(A) %est for Nitrogen: The sodium fusion e/tract is boiled with

iron#--% sulphate and then acidied with

concentrated sulphuric acid. The formation of ;russian blue colour conrms the presence of nitrogen.

 _{*odium cyanide rst reacts with iron#--% sulphate}

and forms sodium he/acyanoferrate#--%.

_{On heating with concentrated sulphuric acid some}

iron#--% ions are o/idised to iron#---% ions which react with sodium he/acyanoferrate#--% to produce iron#---% he/acyanoferrate#--% #ferriferrocyanide% which is

;russian blue in colour.

(B) %est for Sulphur:

#a% The sodium fusion e/tract is acidied with acetic acid and lead acetate is added

to it. 7 black precipitate of lead sulphide indicates the presence of sulphur.

#b% On treating sodium fusion e/tract with sodium nitroprusside, appearance of a violet colour further indicates the presence of sulphur.

(C) %est for &alogens: The sodium fusion e/tract is acidied with nitric acid and then treated with

silver nitrate.

9esults

 _{7 white precipitate, soluble in ammonium}

hydro/ide shows the presence of chlorine.

 _{7 yellowish precipitate, sparingly soluble in}

ammonium hydro/ide shows the presence of bromine.

 _{7 yellow precipitate, insoluble in ammonium}

(') %est for Phosphorus: The compound is

heated with an o/idising agent #sodium pero/ide%.  The phosphorus present in the compound is

o/idised to phosphate. The solution is boiled with nitric acid and then treated with ammonium

molybdate.

esult: 7 yellow colouration or precipitate indicates the presence of phosphorus.

?UATITATI@E AAL>SIS

Carbon and *ydrogen+ 7 known mass of an organic compound is burnt in the presence of e/cess of o/ygen and copper#--% o/ide.

 _{&arbon and hydrogen in the compound are}

o/idised to carbon dio/ide and water respectively.

Observation

 _{The mass of water produced is determined by}

passing the mi/ture through a weighed <"tube containing anhydrous calcium chloride.

 _{&arbon dio/ide is absorbed in another <"tube}

 The increase in masses of calcium chloride and potassium hydro/ide gives the amounts of water and carbon dio/ide from which the percentages of carbon and hydrogen are calculated.



 itrogen

+ There are two methods for estimation ofnitrogen #i% 3umas method #ii%N4eldahlEs method.

(i) 'umas method : The nitrogen containing organic compound, when heated with copper o/ide in an

atmosphere of carbon dio/ide, yields free nitrogen in addition to carbon dio/ide and water.

(ii) *eldahl+s method: The compound containing nitrogen is heated with concentrated sulphuric acid. 8itrogen in the

compound gets converted to ammonium sulphate .

 _{The liberated ammonia gas is absorbed in an}

e/cess of standard solution of sulphuric acid.

 _{The amount of ammonia produced is determined}

by estimating unreacted sulphuric acid left after the absorption of ammonia by titrating it with standard alkali solution.

3rawbacks of this method

-t is not applicable to

compounds containing nitrogen in nitro and ao

groups and nitrogen present in the ring #e.g. pyridine% as nitrogen of these compounds does not change to ammonium sulphate under these conditions.



 *a%ogens

Carius method 

:

7 known mass of an organic

compound is heated with fuming nitric acid in the presence of silver nitrate contained in a hard glass tube known as &arius tube, in a furnace.

 _{&arbon and hydrogen present in the compound are}

o/idised to carbon dio/ide and water.

 _{The halogen present forms the corresponding}

silver halide

Su%phur+

7 known mass of an organic compound is heated in a &arius tube with sodium pero/ide or fuming nitric acid. *ulphur present in the compound is o/idised to sulphuric acid.

_{-t is precipitated as barium sulphate by adding}

e/cess of barium chloride solution in water.

 _{The precipitate is ltered, washed, dried and}

Phosphorus+

7 known mass of an organic

compound is heated with fuming nitric acid where upon phosphorus present in the compound is

o/idised to phosphoric acid.

_{-t is precipitated as ammonium}

phosphomolybdate, by adding ammonia and

ammonium molybdate.

O2ygen+

7 denite mass of an organic compound is decomposed by heating in a stream of nitrogen gas.

 _{The mi/ture of gaseous products containing}

o/ygen is passed over red"hot coke when all the o/ygen is converted to carbon mono/ide.

 This mi/ture is passed through warm iodine pento/ide when carbon mono/ide is o/idised to carbon dio/ide producing iodine.

 _{The percentage of o/ygen can be derived from the}