One-bond 13C–13C coupling constants in alkyl-substituted cyclopropenes: experimental and theoretical studies

✍ Scribed by Krystyna Kamieńska-Trela; Piotr Bernatowicz; Wolfgang Lüttke; Reinhard Machinek; Marit Trætteberg

• Publisher: John Wiley and Sons
• Year: 2002
• Tongue: English
• Weight: 137 KB
• Volume: 40
• Category: Article
• ISSN: 0749-1581
• DOI: 10.1002/mrc.1073

✦ Synopsis

Abstract

Measurements of one‐bond carbon–carbon coupling constants, ^1^J(C, C), were performed for two series of compounds, alkyl‐substituted cyclopropenes and cyclopropanes. The experimental data were complemented by a set of DFT‐calculated J couplings for the parent cyclopropene (1), its methyl and silyl derivatives and, additionally, for 1‐methylcyclobutene (3), 1‐methylcyclopentene (4) and 1‐methylcyclohexene (5) and good agreement was observed between the experimental and the calculated data; all the trends are perfectly maintained, including a dramatic decrease in the couplings across endocyclic single bonds in cyclopropene and its derivatives, and a significant decrease in the corresponding couplings in cyclobutene. Using the data obtained, the s characters of the carbon hybrid orbitals involved in the formation of the cyclopropene were calculated. The results clearly show that the ring closure and the related strain exerted upon the cyclopropene molecule only slightly disturb the electron structure of the double bond. The s character of the corresponding carbon orbital is 0.314 in cyclopropene vs the theoretical value of 0.333 in ethene. This is at variance with the endo‐ and exocyclic single bonds, where the s characters of the orbitals forming the endocyclic single bonds are much smaller than those of the bonds in the open‐chain compounds, i.e. 0.229 (C‐1 and/or C‐2) and 0.166 (C‐3). The s values calculated for the exocyclic CH bonds are 0.334 for C‐3 and 0.456 for C‐1 and/or C‐2. Copyright © 2002 John Wiley & Sons, Ltd.