β-Elimination of 9-fluorenylmethanol in solutions of methanol and t-butyl alcohol

Abstract

In solutions of methan[²H₁]ol containing sodium methoxide, β-elimination of 9-fluorenylmethanol occurs by an E1cB mechanism. The rate of β-hydrogen exchange exceeds that of elimination and the mechanism is established in a manner similar to that for the reaction in D₂O, by analysis of the kinetic induction period upon elimination of undeuteriated substrate in deuteriated solvent. In CH₃OH, as in H₂O, there are indications of a competing elimination mechanism, probably E2. Addition of t-butyl alcohol to methanol leads to an increase in the absolute rates of exchange and elimination and a decrease in their relative rates. In pure t-butyl alcohol, exchange is completely suppressed, and comparison of both the relative rates of tritium exchange of [9-³H₁]9-fluorenylmethanol and [9-³H₁]fluorene, and the isotope effect upon elimination, with values in other solvents suggests that elimination occurs via rate-determining formation of a carbanion intermediate.