WHY ARE METHYLENECYCLOPROPANE AND 1-METHYLCYLOPROPENE MORE STRAINED THAN METHYLCYCLOPROPANE

Ab initio calculations have been performed in order to investigate why the introduction of each trigonal center into a cyclopropane ring res ults in an increase in strain energy of 12-14 kcal/mol. Our calculatio ns find that, as is commonly believed, introduction of a trigonal cent er into a three-membered ring does create some additional angle strain . However, our computational results show that the major source of the additional ''strain'' that results from the introduction of each trig onal center into cyclopropane is not an increase in angle strain but t he loss of a very strong cyclopropane C-H bond.