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Towards a valence‐orbital/bond‐orbital description of biochemical H‐bonds from ab initio calculations
Author(s) -
Zuccarello Felice,
Re Giuseppe Del
Publication year - 1987
Publication title -
journal of computational chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.907
H-Index - 188
eISSN - 1096-987X
pISSN - 0192-8651
DOI - 10.1002/jcc.540080610
Subject(s) - chemistry , valence bond theory , non bonding orbital , molecular orbital , ab initio , molecular orbital diagram , atomic orbital , valence (chemistry) , computational chemistry , pi bond , lone pair , molecular orbital theory , sigma bond , orbital hybridisation , population , atomic physics , crystallography , chemical bond , bond order , bond length , electron , molecule , physics , quantum mechanics , organic chemistry , sociology , crystal structure , demography
We have studied the system NH 3 …H + …HNCH‐CHCH 2 , which is a model for an enzymatic site characterized by an important pi‐electron contribution, with the aim of contributing to the molecular orbital theory of H‐bridge formation and proton transfer. Ab initio canonical orbitals from STO‐3G and 4.31G bases have been determined for various geometrical configurations, and analyzed in terms of Mulliken's Modified Valence Atomic Orbitals obtained by suitable contraction. Also, the orbital correlation diagram has been obtained and discussed. At least two sigma MO's can be considered specific of the H‐bond: they involve the expected hybrids giving rise to stereoelectronic effects associated with the lone pairs of the two heavy atoms. Population analysis suggests that the bridge hydrogen changes its population very little during its motion along the bridge, although its in situ atomic orbital does not change: this means that it acts essentially as a relay center in charge transfer between the two moieties of the H‐bonded complex. As expected on intuitive grounds, charge transfer involves essentially the sigma cores.