Kinetics of the reactions of cyclopropane derivatives. IV. Kinetic isotope effect in the isomerisation of cyclopropylamine

Abstract

Abstract'The high-pressure isotopic rate ratio k~/ k~ for isomerisation of cyclopropylamine and cyclopropylamine-N-d2 is 1.06 at 649-678 K, supporting a mechanism which does not involve migration of hydrogen from the amine group in the rate-determining step.

Kinetics of the thermal decomposition of trans‐1,2‐dicyanocyclobutane

“…This value is surprisingly high since it is approximately twice the value predicted on the basis of the results for cyanocyclopropane, cyanocyclobutane, and the alkyl cyanides. Furthermore, the experimental results [5,7] and transition-state theory calculations [7] for cyanocyclopropane and cyanocyclobutane suggest that the A factor for DCCR should be L1014.4 sec-'. Thus both A and E obtained by Sarner and coworkers appear to be too low unless there is something unusual about two cyano groups acting in concert.…”

“…On this basis, accelerations in rate caused by conjugating substituent groups such as vinyl or phenyl may be explained in terms of resonance stabilization of the intermediate biradicals [3]. Thus comparison of the kinetic data for the thermal reactions of cyanocyclopropane [5] and cyanocyclobutane [6,7] with the results for methylcyclopropanel and methylcyclobutanel leads to values of 5.0 and 5.1 kcal/mol for the radical stabilization energy of the cyano group [S]. These values are strongly supported by recent studies of the very lowpressure pyrolysis of alkyl cyanides [8] which yielded values of 5.1,5.1, and 5.5 kcal/mol for the stabilization energies of the cyanomethyl, a-cyanoethyl, and a-cyanoisopropyl radicals.…”