208517-69-5Relevant articles and documents
The Barrier to Rotation about the Double Bond in Methylenecyclopropane
Roth, Wolfgang R.,Quast, Michael
, p. 763 - 768 (2007/10/03)
Activation parameters have been determined in the gas phase for the geometrical isomenzation of the double bonds in two phenyl-substituted methylenecyclopropanes (2 and 8). Comparison with the analogous values for three sterically non-restricted styrene derivatives (15, 16 and 17) shows that the enthalpies of activation for the methylenecyclopropanes are lower by 3.7 kcal mol-1. This value, which is an upper limit to the amount of strain energy released by pyramidalization of the ring carbon atom in the orthogonal diradical transition state when undergoing geometrical isomerization, is considerably smaller than the value of 12-14 kcal mol-1 by which the strain energy of methylenecyclopropane is larger relative to that of cyclopropane. Our kinetics experiments thus show that the angle strain, associated with incorporating a trigonal carbon atom into the three-membered ring, is not responsible for the majority of the additional strain energy of methylenecyclopropane, relative to that of cyclopropane.
