The secondary deuterium isotope effects on the rates of decomposition of /-butyl peresters of phenylacetic (1), hydratropic (2), , -dimethylphenylacetic (3), and pivalic acids have been determined by infrared, galvinoxyl, and double-labeling methods. The a effects for 1 and 2 are 1.03-1.06 per deuterium. The ß effects for the series are 1.014-1.020 per deuterium. The implications of these effects with respect to the detailed mechanisms of the reactions are discussed. Preliminary investigations2 of secondary deuterium kinetic isotope effects on the decomposition of /-butyl perphenylacetate (1) and /-butyl perhydratropate (2) were carried out as control experiments to test the validity of our expectation that concerted decomposition rates would be sensitive to deuteration. This expectation was based on the idea that the benzylic carbon atoms of the peresters would approach sp2 hybridization in the transition states. The bending frequencies associated with the a-hydrogen atoms might therefore be expected to be reduced.3 The studies of Seltzer on the a effects in azo compound decom-position4 as well as the ß scission of cumyloxy radical5 have indicated that these a effects are of the order of 1.10-1.15 per deuterium atom for these radical-forming reactions. The observed a effects in the preliminary studies were within this expected range while that for the decomposition of acetyl peroxide was much smaller. We therefore concluded that the small value for the latter reaction must be interpreted in terms of a nonconcerted process.The ß effect in the perhydratropate case was also ex-(1)

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A simple model is derived to account for the diffusive behavior of radical pairs which are destroyed rapidly. The implications of this model are discussed.

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sealed, and immersed in a thermoregulated oil bath at 74.0 f 0.1". constants were: in isooctane, k = 1.77 x sec-I and inThe tubes were removed at various time intervals, quenched in ice, paraffin oil. k = 0.91 x sec-'.. read in the spectrometer, and reimmersed in the bath: All rate plots were linear for three half-lives, and the rate constants were obtained by a least-squares treatment2' of the experimental data. The rate Acknowledgment. We wish to express our appreciation to the National Science Foundation and the U. S.Army Research Office, Durham, for financial support of this work. Abstract:A semiempirical equation is derived to connect w-SCF molecular orbital wave functions and eigenvalues with the hyperconjugative contribution to $-secondary deuterium isotope effects. The results of the application of this equation to a number of hydrocarbon systems are discussed. econdary deuterium kinetic isotope effects have been tems," W. A. Benjamin, Inc., New York, N. Y., 1966. (9) L. Salem, "The Molecular Orbital Theory of Conjugated Sys-Koenig, Wolf Hyperconjugative Contribution to Secondary D Effects -, , . ,, , . 90, 7014 (1968). (12) T. Koenig, ibid., 91, 2558 (1969).