Capto-dative substitution and cyclopropane geometry. Part 1. Comparison between capto-dative and di-capto substitution effects on cyclopropane geometry; an X-ray diffraction study

Abstract

To study capto-dative (cd) and di-capto (cc′) substitution effects on cyclopropane geometry the crystal and molecular structures of the following three cyclopropane derivatives have been determined from X-ray diffraction data: 2-t-butylthio-1-r,2-t-dicyano-1-methoxycarbonylcyclopropane(I); 2-t-butylthio-1-r, 2-t-dicyano-1-phenylthiocyclopropane (II); and 2-t-butylthio-1-r,2-t-dicyano-1-phenylcyclo-propane (III). These structures have been solved by direct methods and refined by least-squares using 1 572, 3 729, and 1 768 reflections, respectively, to R= 4.7, 6.4, and 4.0%. In both capto-dative. and di-capto substitution, the distal ring bond is shortened, but the vicinal bonds are lengthened. Although a long C(1)–C(2) ring bond is observed in each compound, this bond is the most stretched one in molecule (I) for which the highest activation energy of thermal cis–trans isomerisation was determined.