Trans-Fused bicyclic cyclopropanes

Another case of increased strain is found with the trans-fused bicyclic cyclopropanes. With an eight-membered ring, the cis- and trans-fused compounds have essentially the... 

The structures of bicyclic and polycyclic small-ring compounds have attracted some interest. The relationship between the C-C-H bond angles at the bridgehead of bicyclo[1.1.0]butane (2) and the angle between its cyclopropane rings has been studied.31 Bicyclobutane and most other cyclopropane derivatives have bonds that are formed from orbitals that are bent in the same direction. However, with some tran.v-fused bicyclic compounds containing a cyclopropane... 

In Table 6, which was compiled from work on bicyclo[n.l.O]alkanes, bicyclo[1.1.0]-butanes, bicyclo[2.1.0]hexanes, bicyclo[2.2.1]heptanes , bicyclo[3.1.1]heptanes bicyclo[2.2.2]octanes ", bicyclo[3.3.0]octanes", bicyclo[4.n.0]alkanes, bicyclo[3.3.13-nonanes" spiro[4.5]alkanes" and trans-decalins the chemical shifts of several bicyclic alkanes are tabulated. The values were mainly explained by the steric effects present in the different structural environments, with the exception of fused cyclopropane rings (see below). 

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