Study of Softness Indices and Activity Parameters in
Isomeric Diazines by DFT Method
M. B. Kalhans
Department of Chemistry,
Bareilly College, Bareilly, (U.P.) 243005, INDIA. email : [email protected].
(Received on: August 19, 2019)
ABSTRACT
DFT method is more advance and gave better results than Hartree-Fock calculations. Quantum mechanical frame work of HSAB principle was given by Klopmann. The values of Em# for the two nitrogen’s were calculated, by applying DFT, which gave important results about the activity.
Keywords: DFT, HSAB, Quantum mechanical.
INTRODUCTION
Complexes of Pyrazine 2-Carboxomide (PZA), Pyrazine 2, 3-dicarboximide (PZD) and 2-Amino Pyrimidine with CoM (NCS)4 and NiM (NCS)4 (M=Zn, Cd, Hg) has been
prepared and characterized by elemental analysis, molar conductance, magnetic measurements, infrared and electronic spectral techniques1-10. Chemical hardness (η) and density functional theory was given by Parr. Pearson and Parr defined η and gave an empirical method of evaluating it11. The time dependent DFT is based on time dependent schrodinger wave equation
iℏ ∂ψ = T + U + V + d ϕ n(r) ψ( ) (1)
Where T and U are kinetic and interaction energies and V =∫drν (r)n(r) is electrostatic environment. Drago developed an equation for enthalpy of adduct formation for neutral molecules12. The equation developed by Dewart et al. gave better results13
Orbital free DFT has a predictive power too limited for most practical demands. The search for more accurate representation of the kinetic energy in terms of n-functionals is at present an active field of research14.
MATERIAL AND METHODOLOGY
The calculations are made by magnetic neglect of diatomic overlap (SCF) method with standard parameter and molecular geometries completely optimized with in a group by employing BFGS algorithm15-16. Before starting an MNDO (SCF) optimization the initial
geometry was preoptimised by minimizing the root mean square deviation of all bond lengths from a common standard 1.42 Ȧ. The most important quantum mechanical framework of HSAB principle17 was given by G. Klopmann18. This concept was based on charge and frontier
orbital controlled chemical reactions and summarized the reacting species in terms of hard and soft acid and bases. The solution that was introduced for ab-initio Hartree-Fock and has been used for DFT has been to add a classical two centre potential with a damping function for short distances to the DFT Hamiltonian19. We employeed Klopmann equation in the high of DFT
with the help of MOZYME technique by which the computational effort scales for big molecules20.
The density of electron in various orbitals of an atom in bonded state is represented by AOEP. The contribution of electrons in each occupied molecular orbital in Pyrimidine, Pyrazine and Pyridazine and calculated by using population analysis method, introduced by Mulliken21 and given in Table No. 1.
Bond orders and angle of Twist are the structural indices of a molecule which represents the basic comfortability and thereby the stability of molecule. The values of bond order and angle of twist, among the isomeric diazines are calculated and given in Table No. 2 & 3. The values of IP, EA, charge (q), electron density, electronegativity, radius of atom, fukui function, density distribution function have been calculated at both the hetero atoms i.e. N1 & N2 in three isomeric diazines. On substituting these values in Klopmann equation the
softness values E at N1 and N2 have been evaluated table 4 & 5.
RESULTS AND DISCUSSION
The sequence of bond orders of the various bonds in the isomeric diazines is of order (C1=C2) Pyridazine > Pyrimidine; (C2-C3) Pyridazine > Pyrimidine > Pyrazine (C3=N4)
Pyrazine > Pyrimidine > Pyridazine; (N4-C5) Pyrazine > Pyrimidine; (C5=N6) Pyrimidine >
Pyrazine; (C1-H7) Pyridazine > Pyrimidne. The summation values of bond order and bond
lengths of the three isomers are (Pyrazine) 12.344107, 11.242917; (Pyridazine) 12.372261, 11.184144; (Pyrimidine) 12.324434, 11.243325. From the calculation of angle of twist it has been established that the two half planes passing through atoms C2, C3, N4 and C3, N4 and C5
is about 1800. Tables 1 and 2 provides the E values for in the ring nitrogen’s in the three isomers have the following order.
Pyrazine > Pyrimidine > Pridazine
N1 5.399143 5.232797 4.409666
N2 5.403844 5.215106 4.418484
Table-1
AOEP’s of the MO’s in three isomeric diazines
Molecular Orbitals Pyrimidine Pyrazine Pyridazine C0=N5 (π) 1.20503 1.61092 1.18567 C0=N5 (σ) 0.92497 1.08254 0.95535 C3=N4 (π) 0.97472 1.30372 0.98465 C3=N4 (σ) 0.91712 1.04511 0.98358 C1=C2 (σ) 1.19356 1.21274 1.1858 C1=C2 (π) 1.19356 1.21274 1.1858
C1-C2 (π) 0.96694 0.94077 0.95536 N4-N5 (σ) 0.99327 0.97707 0.98453 C2-C3 (σ) 1.04793 0.9774 0.98364 C6-C1 (σ) 1.20541 1.21287 0.121756 C1-H7 (σ) 0.99044 0.99959 1.00474 C2-H8 (σ) 0.90937 0.91883 0.92024
C3-H9 (σ) 0.91712 0.97727 0.97308 C6-H10 (σ) 1.62552 1.61155 1.63828 Non-Bonding-I 1.07194 1.08209 1.04819 Non-Bonding-II 1.31561 1.30272 1.29503
C6-H10 (σ*) 1.10438 1.04547 1.04336 C3-H9 (σ*) 1.23697 1.2128 1.63796 C2-H8 (σ*) 0.91597 0.94099 1.04882 C1-H7 (σ*) 0.96662 0.97731 1.29537 C6-C1 (σ*) 0.90906 0.97727 1.04317 C2-C3 (σ*) 1.62538 1.21273 1.21735
Table-2 Bond orders between various atoms in isomeric diazines
Bond Pyridazine Pyrimidine Pyrazine C1 – C2 1.415311 1.408602 1.44627
N1=C2 C2 – C3 1.425949 1.407667 1.384812 C3 – N4 1.394166 1.434368 1.440278 N4 – N5 1.478918 1.411438
N4–C5
1.439586 N4–C5 N5–C6 1.39419 1.412475
C5–N6
1.38548 C5–C6 C6–C1 1.425988 1.433401
N0–C1
1.439657 C0–N1 C1–H7 0.963718 0.95442 0.953458
C2–H2 C2–H8 0.963679 0.962918 0.953551
C1–H8 C3–H9 0.955202 0.954426 0.953544
C5–H9 C6–H10 0.95514 0.944716
C5–H10
0.953471 C6–H10
Table-3 Twist angle among various atoms of Diazines
Type of Bond Pyrazine Pyrimidine Pyridazine N1-C2-C3=N4 0.037055 0.013731
C1=C2-C3-N4
0.037055
C2-C3-C4=C5 0.009603 0.006242 0.009603 C3=N4-C5-C6 0.00762 0.00131 0.00762 C3=N1-C2-H7 179.9842 179.9973
C3-C2=C1-H7
179.9842
N4-C2-C3=H8 179.9916 179.9915 C3-C1-C2=H8
179.9916
C6-N4-C5-H9 179.9993 179.9985 N4-C2-C3-H9
179.9993
N4-C5-C6-H10 179.9847 197.9837 N6-N4-C5=H10
179.9847
Table-4 Values of different parameters of three isomeric diazines at N1 Parameter Pyridazine Pyrimidine Pyrazine
Table-5 Values of different parameters of three isomeric diazines at N2 Parameter Pyradazine Pyrimidine Pyrazine
Ionisation potential 14.88113 16.16142 15.10855 Electron Affinity -4.442097 -5.456943 -4.506892 Charge -0.025316 -0.117586 -0.041831 Atom electron density 1.63796 1.62538 1.61155 Electronegativity 5.219515 5.35224 5.30683 Radius of atom 0.74 0.74 0.74 Fukui function 0.2339943 0.2321972 0.2302214 Density distribution fn 11.2759 11.1893 11.09409 Softness of atom E 4.418484 5.215106 5.403844
CONCLUSIONS
The values of softness parameters, E for the three isomeric diazines shows that basic softness, E i.e. tendency to donate electrons is maximum in Pyrazine and minimum in Pyridazine the pka values of the three molecules also support the above fact. In case of Pyrazine the two ring introgens are at para position i.e. at maximum distance to each other. A minimum pka value for proton gained (0.701) for Pyrazine also confirm the maximum basic strength of Pyrazine.
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