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Die Bindungsenergien der Kohlenwasserstoffe
Author(s) -
Heitler W.
Publication year - 1955
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.19550380103
Subject(s) - chemistry , dissociation (chemistry) , binding energy , excitation , valence (chemistry) , bond dissociation energy , atomic physics , thermodynamics , computational chemistry , quantum mechanics , physics , organic chemistry
The binding energies of the simple hydrocarbons CH 4 , C 2 H 2 , C 2 H 4 , C 2 H 6 and certain radicals are calculated under the assumption that only the 5 S‐state of carbon contributes essentially to the binding. The justification for this procedure is discussed in 1. For the calculation the method of valence structures first developed by Rumer, Weyl and the present author is used. At first the interaction between non‐neighbours is neglected, but the repulsion between the H‐atoms in CH 4 , CH 3 , etc. is taken into account. The interaction of these (for the known HH distances) is known and so is the excitation energy of 5 S. Then 4 unknown parameters occur, namely the Coulomb and exchange integrals between C and C and between C and H. It turns out, however, that the results depend essentially on 3 parameters only. These are determined from the binding energies of CH 4 , C 2 H 2 and C 2 H 6 . Two sets of experimental values are considered according to the two possible (as yet undecided) values of the heat of evaporation of diamond of 141 and 170 kcal/mol. After the values of the integrals are fixed the binding energy of C 2 H 4 and the dissociation energies CH 4 → CH 3 + H, C 2 H 2 → C 2 H + H and C 2 H 6 → C 2 H 5 + H can be calculated and compared with the experiments (Table 1). The agreement is excellent, the error is in each case less than 6%. Thus the theory leads to an understanding of the values of the CC, CC, CC bonds and the different dissociation energies required to remove one hydrogen atom. If the interaction of non‐neighbours is taken into account, an equally good agreement can be reached provided that certain plausible conditions about this interaction are fulfilled.