Group strain energy

Conformational free energies (-AG ) for substituent groups Strain energies of cycloalkanes... 

Calculation of group increments for oxygen, sulfur and nitrogen compounds has allowed the estimation of conventional ring-strain energies (CRSE) for saturated heterocycles from enthalpies of formation. For 1,3-dioxolane, CRSE is about 20 kJ mol . In 2,4-dialkyl-l,3-dioxolanes the cis form is always thermodynamically the more stable by approximately 1 kJ mol" . 

Diaxial interaction (Section 4.8) The strain energy caused by a steric interaction between axial groups three carbon atoms apart in chair cyclohexane. 

To summarize in contrast to the observed nucleophilic attack of strongly basic nucleophiles on the sulfonyl and sulfoxy sulfur of the three-membered ring sulfones and sulfoxides, the acyclic sulfone and sulfoxide groups are attacked by nucleophiles only with difficulty Although the precise reason for this difference is as yet not clear, it is most probably associated with the geometry, electronic structure, bonding and strain energy of the cyclic compounds. 

---