Cyclization Tendency versus Ring Size

The strain in ring structures is of two types—angle strain and conformational strain. Ring structures of less than five atoms are highly strained due to the high degree of angle strain, 

TABLE 2-7 Heats of Combustion and Strains of Cycloalkanes per Methylene Group  

6 Calculated as the heat of combustion per methylene group minus the value (659.0) for the n alkane methylene group. 

The general order of thermodynamic stability of different-sized rings is given by 

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Polymerization of a series of dienes of formula [106] has been studied (/i, 16, 93). The polymers that were obtained consisted of both soluble and cross-linked, insoluble fractions. Quantitative infrared and bromination experiments indicated that the soluble polymers possessed cyclic as well as open-chain structures. The percent of cyclization depended on the size of the incipient cycle and corresponded roughly to what is obtained in other cyclization reactions. The results are summarized in the accompanying table. A similar effect of ring size versus tendency toward cyclopolymerization was observed for monomers of structures [107] (92). 

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