Another line of objection comes from Berson (2008), who discusses the significance of very weakly bonded molecules. For example, there are four structural isomers of 2-methylenecyclopentane-1,3-diyl. The most stable of the structures does not correspond to a normal bonding interaction because of an unusually stable singlet state, a state where the electron spins are parallel. Berson suggests that this is a case where “the formation of a bond actually produces a destabilized molecule.” In other w