Cyclopropane strained hydrocarbon reactivity

With the initial synthesis of cyclopropane in 1882 , and the report of its thermal structural isomerization to propene in 1896, this simplest of cyclic hydrocarbons began its extraordinarily fruitful stimulation of fresh insights on fundamental problems in organic chemistry, ranging from basic concepts of ring strain and structural isomerism to questions of thermochemistry and reactivity and of a aromaticity And from the beginning there was controversy, extending a few years before suitably authoritative commentators confirmed the fact that cyclopropane is indeed converted thermally to propene. ... 

The details of any discussion of strain energy are very dependent on the model chosen and this chapter is no exception. However, this fact should not detract from the fact that extra or reduced strain of substituted species relative to the parent hydrocarbon are real phenomena which may be correlated with the degree of reactivity or ease of isomerization. The present chapter begins with a quantitation of the stabilization and destabilization energies and enthalpies associated with monosubstituted cyclopropanes. The approach involves collection of all relevant thermochemical and good calculational data. Conclusions concerning the sensitivities of cyclopropanes to conjugative and electrostatic effects are drawn from both qualitative theory and formal correlation analysis of these... 

Marks has examined the reactivity of thorium metallacycles with hydrocarbons, where ring strain is used to provide the thermodynamic driving force for alkane activation in a reaction with methane (Eq. 17). Reaction with CD4 shows a dramatic kinetic isotope effect, with kH/kD=6, which is typical of the four-centered electrophilic transition state hydrocarbon activations [76]. The metallacy-cle is formed by the elimination of neopentane from the bis-neopentyl derivative [77]. Reaction with cyclopropane and tetramethylsilane gave the bis-cyclopropyl product Cp 2Th(c-propyl)2 and the bis-TMS product Cp 2Th(CH2SiMe3)2, respectively [78]. 

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