Ab initio stability study of the geometric isomerism of acyclic imines and O-protonated carbonyl compounds: Part II. Model compounds for additive schemes of anti-syn conversion energies: imino- and O-protonated derivatives of propynal, butynone and butynonal

Abstract

The problem of decomposing the conversion energies of the geometrical isomers of acyclic isoelectronic imines and O-protonated carbonyl compounds into intuitive contributions associated with the repulsive intramolecular interactions of imino hydrogen atoms (hydroxyl hydrogen atoms) with hydrogen atoms bound to neighbouring carbon atoms is considered. The investigation was based on quantum chemical computations at the Hartree-Fock level with the 6-31G ∗ and 6-31G ∗∗ basis sets for 14 acyclic imines, 14 O-protonated carbonyl species, 10 model imines and 10 model O-protonated systems. Definitions of specific (1,4 and 1,5) hydrogen contributions ( E 14 and E 15) and rules for decomposing the conversion energies into additive contributions are proposed. Application of the procedure to the geometrical isomers of model compounds (imines HCXXXC·CH:NH, HCXXXC·C(:NH)·CH:CH 2, HCXXXC·C(:NH)CHO, HCXXXC·C(:NH)CH:NH, HCXXXC·C(:NH)CH 3, and O-protonated species HCXXXC·CH:Op, HCXXXC·C(:Op)CH:CH 2, HCXXXC·C(:Op)CH 3 HCXXXC·C(:Op)CH:O and HCXXXC·C(:Op)CH:NH) (p denotes a proton) gives zeroth-order estimates of particular contributions. These estimates were used to determine a set of specific contributions, which in turn permit one to reconstruct the conversion energies of the geometrical isomers of acyclic isoelectronic imines and O-protonated carbonyl compounds by using a simple additive scheme. The conversion energies were reproduced to within 0.2–0.3 kcal mol −1. The contribution terms are expected to be fairly generally applicable.