Rotational barriers of strained olefines.
For olefins such as Me3CCH:CEtCMe3, heats of formation have been derived from heats of hydrogenation and force-field calcns. From the kinetics of their geometrical isomerization the corresponding values for the transition states were obtained. The rotational barriers, which vary by nearly 30 kcal/mol, can be described by a unique torsional potential (65.9 +- 0.9 kcal/mol), which is independent of the degree of substitution, if a correction is made for the steric energy contribution in the ground and transition states.
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