ISSN:
0020-7608
Keywords:
Computational Chemistry and Molecular Modeling
;
Atomic, Molecular and Optical Physics
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The difference between the expectation values of the total electronic kinetic energy operator (ΔEK), and the operators accounting for the Coulombic interactions between the electrons and nuclei (ΔVen), between all pairs of electrons (ΔVee), and between all pairs of nuclei (ΔVnn) for the product and reactant species in a wide variety of hydrocarbon reactions are calculated using single determinant basis set data reported in the literature. Following Allen, their contributions to ΔET, the difference between the corresponding total molecular energies and thus the reaction heat, are grouped together as a repulsion energy term, ΔErep = ΔEK + ΔVee + ΔVnn, and an attraction energy term ΔEattr = ΔVen. For all but 2 of the 71 individual reactions considered in this paper, the experimental reaction heat at 0°K corrected for zero-point energy contributions, (ΔH00)zpe, is the result of near compensation between far larger ΔErep and ΔEattr terms, in sharp contrast to the much smaller ΔErep and ΔEattr terms which are characteristic of many molecular rotation processes. By matching the sign of (ΔH00)zpe with that of ΔErep or ΔEattr, as the case may be, the reactions are classified as attractive-dominant or repulsive-dominant (46 in the former class and 23 in the latter), a property which is independent of the direction in which the reaction is written. The sign and magnitude of ΔVee, ΔVnn, and ΔVen and reaction category are discussed in relation to the various kinds of structural change involved in going from reactants to products. For the vast majority of reactions, the numerical relationship ΔVee ≈ ΔVnn has been found to hold to within a few percent.
Additional Material:
15 Tab.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/qua.560130303
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