CORRELATION BETWEEN EXOTHERMICITY, RATE, AND NEGATIVE TEMPERATURE-DEPENDENCE IN SLOW ION-MOLECULE REACTIONS

The rate constants (K450) of 22 H-transfer reactions between C2-C7 carbonium ions and C3-C10 cyclic and acyclic hydrocarbons were measured. The values of k450 range between 2.2×10-9 and 3×10-13 cm3/mol.s, corresponding to collision efficiencies of approximately 1 to 10-4. The rate constants exhibit large negative temperature coefficients of the form k = AT-n, n = 1.5-6.8. A direct relation between k450 and exothermicity is observed. An inverse linear correlation between Iπ k450 and the magnitude of the negative temperature coefficient (n) is also noted. © 1978, American Chemical Society. All rights reserved.