Strain and conformation

Stereochemical constraints in cyclic sulfones and sulfoxides impart increased weight to strain and conformational factors in the generation of carbanions and their stability, causing distinct differences between the behavior of cyclic and open-chain systems233, due primarily to the prevention of extensive rotation about the C —S bond, which is the major way that achiral carbanions racemize. Study of the a-H/D exchange rate fce and the racemization rate ka may provide information concerning the acidity-stereochemical relationships in optically active cyclic sulfone and sulfoxide systems. 

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,... 

Jencks WP. Strain and conformation change in enzymatic catalysis. In Current Aspects of Biochemical Energetics. Kennedy EP, ed. 1966. Academic Press, New York, pp. 273-298. 

The Origin of Ring Strain and Conformational Flexibility in Tri- and Tetrasiloxane Rings and Their Heavier Group 14 Congeners... 

Valuable preparative applications are rare and especially in ring-forming reactions other stereochemical factors such as ring strain and conformational effects will determine the stereochemistry. However the use of metal compounds to influence regio- and stereo-selectivity continues to excite interest. For C—C bond formation the coupling of allylic acetates with organocuprates offers broad synthetic potential as it generally seems to proceed with double bond shift. ... 

Strains and conformational compression of the substrate at the enzyme active site were also proposed to explain the rate acceleration by chorismate mutase [66, 70,... 

Aspects of ring strain and conformational analysis are discussed in Sections 4-2 through 4-5. 

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