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The Structure of Hydrazoic Acid

K. Singh
Proceedings of the Royal Society of London. Series A, Mathematical and Physical Sciences
Vol. 225, No. 1163 (Sep. 22, 1954), pp. 519-534
Published by: Royal Society
Stable URL: http://www.jstor.org/stable/99521
Page Count: 16
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The Structure of Hydrazoic Acid
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Abstract

The structure of hydrazoic acid is described in terms of bond order, formal charge and hybridization. Calculations by the molecular orbital method show that the orders of N$^{1}\chembond{1,0} $N2 and N$^{2}\chembond{1,0} $N3 bonds in hydrazoic acid H$\chembond{1,0} $N$^{1}\chembond{1,0} $N$^{2}\chembond{1,0} $N3 are 1· 65 and 2· 64 respectively. The distribution of charge on N1, N2 and N3 atoms is found to be -0· 29, +0· 61 and -0· 31 respectively. The orders of these bonds have also been derived by the valence-bond method. In accordance with Penney's definition the orders of bonds between N1 and N2, and N2 and N3 atoms have been found to be 1· 67 and 2· 67 respectively. In order to obtain an insight into the relative importance of the three factors, the heat of formation of hydrazoic acid has been calculated. With the help of the principle of additivity of bond energies and the method of localized electron pairs the heat of formation of hydrazoic acid EHN3 can be expressed in terms of σ -bond energy K, exchange integral J, repulsion energy between two lone pairs of electrons R, and promotional energy P. The expression obtained is of the form EHN3 = EN-H + (K1 - 1/2J1) + (K2 + 1/2J2) + √ (J1 2+J2 2-J$_{ 1}$J2)-1/2R-P, where EH-N is the energy of the N$\chembond{1,0} H$ bond and the suffixes 1 and 2 refer to bonds between the N1 and N2, and N2 and N3 atoms respectively. The numerical calculations show that EHN3 has a minimum value of energy of 315· 8 kcal for the lengths of N$^{1}\chembond{1,0} $N2 and N$^{2}\chembond{1,0} $N3 bonds equal to 1· 26 and 1· 13 Å respectively. If allowance is made for the increase in energy arising from the presence of formal charge and increased hybridization on the central nitrogen atom, EHN3 has a minimum value of 319· 1 kcal for lengths of N$^{1}\chembond{1,0} $N2 and N$^{2}\chembond{1,0} $N3 bonds equal to 1· 24 and 1· 12 Å respectively. These calculated values of interatomic distances and the heat of formation agree with the experimental values.

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