Secondary deuterium isotope effects in the solvolysis of cyclopropyl triflates

α Deuterium isotope effects have been measured for solvolysis of cyclopropyl triflate, exo-bicyclo[4.1.0]hept- 7-yl triflate, exo-bicyclo[3.1.0]hex-6-yl triflate, and endo-tricyclo[3.2.1.024]oct-exo-3-yl triflate in acetic acid. The respective values are 1.07, 1.08, 1.18, and 1.24. These values are discussed in terms of increasing cyclopropyl cationic character in the cationic intermediates. β-Deuterium isotope effects were determined for 1-methyl cyclopropyl triflate (8) and endo-6-methyl-exo-bicyclo[3.1.0]hex-6-yl triflate (9). Values were 1.12 and 1.42, respectively. The former value was considered to implicate a concerted ionization ring opening in 8. The latter value was consistent with a stepwise ionization, ring opening mechanism for 9. The β effect of 1.42 was considered small in view of the instability of the cation derived from 9 and rationalized in terms of an early transition state