Transitions alkyl chain branching effects

Again, approximately half of this effect will already be felt at the transition states for insertion and chain transfer. Thus, internal olefins are inserted less easily, oc-branched alkyls are more reactive towards insertion, and secondary alkyls tend to isomerize to primary alkyls. The abnormally low reactivity of Al—Me bonds towards olefin insertion must probably be explained in this way. The high reactivity of (f-Bu)3Al towards ethene insertion, despite its significant steric hindrance, might in part be due to the same effect. 

Table 30 contains transition data on some compounds with terminal small rings (compounds 2 and 3). Compared with the simple alkyloxy group (compound 1), the small rings have an effect comparable to branched alkyls, but unlike that of five- or six-mem-bered rings. In order to obtain chiral materials, the introduction of an oxirane or thi-irane ring in the terminal chains is useful [143]. 

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