The effect of carbonyl substitution on the strain energy of small ring compounds and their six-member ring reference compounds.
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.
Bach
Robert D
RD
Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware 19716, USA. rbach@udel.edu
Dmitrenko
Olga
O
D003510:Cyclohexanes / Q000737:chemistry*; D003521:Cyclopropanes / Q000737:chemistry*; D005027:Ethylene Oxide / Q000737:chemistry; D007769:Lactams / Q000737:chemistry*; D007783:Lactones / Q000737:chemistry*; D013329:Structure-Activity Relationship; D013816:Thermodynamics
D003510:Cyclohexanes; D003521:Cyclopropanes; D007769:Lactams; D007783:Lactones; D005027:Ethylene Oxide