Ethylene torsional strain

In 1972, Mock considered double-bond reactivity and its relationship to torsional strain, by which he understood the strain imposed on a double bond in medium-ring fra 5-cycloalkenes or by steric compression of large cis substituents [28]. He argued that the loss of 7t overlap due to a torsion about the double bond can be partially compensated by rehybridization in these two situations, leading, respectively, to syn and anti pyramidalization of the double bond consequently, such bonds will favor different modes of addition (cis and trans). The proposition was supported by examples of X-ray structures of strained olefins, STO-3G energy calculations for the twisted and pyramidalized ethylene geometries, and by analysis of the out-of-plane vibrational frequencies of ethylene. Mock concluded that small ground-state distortions may produce sizable effects in the transition states. 

The reaction coordinate diagrams for nucleophilic attack of hydroxide ion on ethylene oxide and on diethyl ether. The greater reactivity of the epoxide is a result of the strain (ring strain and torsional strain) in the three-membered ring, which increases its free energy. 

Dynamic measurements through the melting region of polymers can only be achieved with difficulty and require parallel-plate, simple-shear, or torsion geometry. Polyethylene shows at least two, if not three transitions [14, 15] which depend on polymer type (linear, linear low, etc.). Poly(chlorotrifluoro-ethylene) has also been studied in detail [16]. In reality these data are all related to the lamellar structures formed in these systems. Poly(ethylene oxide) also exhibits loss peaks through the melting region, but their amplitude has been observed to be strain-dependent. The polymer is non-linear viscoelastic, and quantification of the measurements is difficult. This probably applies to most ac relaxations. 

---