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A Quantitative Assessment of „Through‐space”︁ and „Through‐bond”︁ Interactions. Application to Semi‐empirical SCF Models
Author(s) -
Heilbronner Edgar,
Schmelzer Andreas
Publication year - 1975
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19750580331
Subject(s) - chemistry , mindo , antisymmetric relation , computational chemistry , molecular orbital , atomic orbital , molecular orbital theory , cndo/2 , molecular orbital diagram , localized molecular orbitals , valence bond theory , quantum mechanics , physics , electron , molecule , mathematical physics , organic chemistry
The scheme of ‘through‐space’ and ‘through‐bond’ interaction of (semi)localized orbitals, originally proposed by Hoffmann , is reexamined in terms of SCF many‐electron treatments. It is shown that the two types of interaction can be characterized by examining the corresponding off‐diagonal matrix elements of the Hartree ‐ Fock matrices of the localized or the symmetry adapted localized orbitals and of the partially diagonalized Hartree ‐ Fock matrices referring to ‘precanonical orbitals’. The procedure outlined is applied to three practical examples using the semiempirical many‐electron treatments SPINDO, MINDO/2 and CNDO/2: a A reassessment of ‘through‐space’ and ‘through‐bond’ interaction in norbornadiene indicates, that the latter type of interaction is also of importance for the orbital based mainly on the antisymmetric combination of the localized x‐orbitals. The differences in the predictions derived from the three models are critically examined. b The competition between ‘through‐space’ and ‘through‐bond’ interaction in the series of bicyclic dienes from norbornadiene to bicyclo[4.2.2]‐dcca‐7,9‐diene and in cyclohexa‐1,4‐diene, i . e . their dependence on the dihedral angle UI is reexamined. It is found that the rationalization for the orbital crossing near ω = 130° deduccd from PE. spectroscopic data can not be as simple as originally suggested and that the relay’ orbitals responsible for ‘through‐bond interaction affecting both the symmetric and the antisymmetric combination of the π‐orbitals extend over the whole CC‐σ‐system of the six membered ring. c ‘Through‐bond’ interaction of the two lone pair orbitals in 1,4‐diazabicyclo[2.2.2]octane is found to be large for their symmetric and the antisymmetric linear combination.The analysis quoted, draws attention to some of the dangers involved in using semiempirical treatments for the interpretation of PE. data in terms of Koopmans ′ theorem, without due caution.