The first to comment on the unusual effects of fluorine substitution on cyclopropane were O'Neal and Benson'who estimated that an increase in ring strain of 4.5-9 kcal/mol per fluorine substituent was produced. Hoffman predicted that fluorine should weaken the bond opposite the carbon bearing the fluorine substituent whereas the adjacent bonds should be slightly strengthened. 2 In a series of studies to obtain quantitative data on the kinetic and ...