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Ab initio and density functional studies on bonding nature of the NN bonds in 1,2,5‐trinitroimidazole and 1,2,4,5‐tetranitroimidazole
Author(s) -
Cho Soo Gyeong,
Park Bang Sam
Publication year - 1999
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/(sici)1097-461x(1999)72:2<145::aid-qua7>3.0.co;2-0
Subject(s) - bond length , chemistry , ab initio , basis set , bond order , ionic bonding , electronic correlation , computational chemistry , sextuple bond , density functional theory , molecular geometry , bond energy , electron density , perturbation theory (quantum mechanics) , crystallography , molecule , electron , ion , physics , crystal structure , quantum mechanics , organic chemistry
The bonding nature of the NN bonds in 1,2,5‐trinitroimidazole ( I ) and 1,2,4,5‐tetranitroimidazole ( II ) was examined with various levels of ab initio and density functional (DF) theories. The second‐order Møller–Plesset perturbation method (MP2) with the 6‐31G** basis set has predicted significantly long NN bond lengths in I and II , that is, 1.737 and 1.824 Å, respectively. Two DF theories, BLYP/6‐31G** and BP86/6‐31G**, provided similar results to those of MP2/6‐31G**. On the other hand, Hartree–Fock (HF) calculation with the 6‐311++G** basis set evaluated these bond lengths of I and II to be 1.443 and 1.414 Å, respectively. Bond properties including the bond critical density are strongly dependent on the equilibrium bond length. Thus, accurate prediction of geometric parameters is of particular importance to derive reliable bond properties. Especially, a substantial difference in bonding properties is observed when the electron correlation effect is included. According to our analyses with bonding natures and CHELPG charges at the MP2 level, (1) the NN bonds of I and II appear to have a significant ionic nature, and (2) the 1‐nitro group bears a considerable positive charge and has attractive electrostatic interactions with O atoms of adjacent nitro groups. Although all the theories utilized in this study predict that both I and II are stable in their potential‐energy surfaces, significantly long NN bond lengths calculated with MP2 and DF theories imply a strong hyperconjugation effect, which may explain a tendency to form a salt in these compounds easily. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 72: 145–154, 1999