The Effect of Carbonyl Substitution on the Strain Energy of Small Ring Compounds and Their Six-Member Ring Reference Compounds

摘要

High level ab initio calculations have been applied to the estimation of ring strain energies (SE) of a series of three- and six-member ring compounds.The SE of cyclohexane has been estimated to be 2.2 kcal/mol at the CBS-APNO level of theory.The SE of cyclopropane has been increased to 28.6 kcal/ mol after correction for the one-half of the SE of cyclohexane.The SEs of a series of carbonyl-containing three-member ring compounds have been estimated at the CBS-Q level by their combination with cyclopropane to produce a six-member ring reference compound.The SEs of cyclopropanone (5),the simplest alpha-lactone (6) [oxiranone],and alpha-lactam (7) [aziridinone] have been predicted to be 49,47,and 55 kcal/mol,respectively,after correction for the SE of the corresponding six-member ring reference compound.The SEs of cyclohexanone,delta-valerolactone,and delta-valerolactam have been estimated to be 4.3,11.3,and 5.1 kcal/mol,respectively.Marked increases in the SE of silacyclopropane and siladioxirane have been established,while significant decreases in the SEs of phosphorus,sulfur,dioxa- and diaza-containing three-member ring compounds were observed.The ring strain energies of the hydrocarbons (but not heterocycles) exhibit a strong correlation with their C-H bond dissociation energies.