A survey of kinetic, secondary deuterium isotope effects, for a, ,!I, and y deuterated alkyl halides reacting with pyridine in nitrobenzene solvent has been made. a-Deuterium effects have been measured for eight compounds, P-deuterium effects for four compounds, and one rate ratio for y-deuteration is reported. The possible errors in the rate ratios for b-deuterated compounds, resulting from the elimination side reaction have been determined. The results are discussed in terms of transition state structure.Une etude sur la cinetique des effets isotopiques secondaires du deuterium a kt6 effectuee sur les halogenures d'alkyle a, /I, et y deuteres qui reagissent avec la pyridine dans le nitrobenzine. Les effets du deuterium en a ont ete mesures au moyen de huit composes, les effets du deuterium en au moyen de quatre composes, et on rapporte un rapport de vitesse pour la deuteration en y. Leserreurs possibles dans les rapports de vitesse pour les composes ,!I-deuterts, et qui resultent d'une reaction annexe d'elimination, ont ete determinees. Les resultats sont discutes en fonction de la structure de I'etat de transition.Canadian Journal of Chemistry, 50,986 (1972) Introduction Although many secondary deuterium isotope effects have been measured for nucleophilic substitutions at saturated carbon, systematic studies involving changes in the leaving group, the alkyl group, and the position of deuteration are not common. Robertson and co-workers (1-4) have provided the most complete set of data for sclvolysis reactions in water of alkyl halides and sulfonates, and Brown and McDonald (5) have reported a series of measurements on various substituted deuterated pyridines reacting with alkyl iodides in nitrobenzene solvent. This paper presents a set of isotopic rate ratios for the reaction of a single nucleophile pyridine, with various deuterated alkyl compounds in the same solvent, nitrobenzene.

Secondary kinetic deuterium isotope effects are presented for the reaction of methyl-d3 iodide and pyridine in four different solvents. Calculations on mass and moment of inertia change with deuteration in the initial state and an assumed tetrahedral transition state, together with internal rotational effects, are used to rationalize the inverse isotope effects. It is concluded from the variation of the isotopic rate ratio, that the transition state structure varies with solvent.Les effets secondaires isotopiques cinetiques de deuterium sont presentes pour la reaction de I'iodure de methyle d3 et la pyridine dans quatre solvants differents. Les calculs de masses et de moments d'inertie qui varient avec la deuteration dans I'etat initial et un etat de transition tetrahedrique suppose, conjointement avec les effets de rotation interne, sont utilise pour rationaliser les effets isotopiques inverses. On conclut de la variation du rapport des vitesses isotopiques que la structure de I'etat de transition varie avec le solvant.

The temperature dependence of the isotope effect for the reaction of dimethylaniline and dimethyld6-aniline with methyl p-toluenesulfonate in nitrobenzene solvent has been measured, yielding the The significance of the correlation is discussed and a possible rationalization, in terms of mechanism and particularly the role of the solvent is given.Canadian Journal of Chemistry, 49. 439 (1971) Introduction Kaplan and Thornton (1) have studied the effect of deuterium substitution for the methyl hydrogens of N,N-dimethylaniline on the rate of the quaternization reaction of the amine with methyl p-toluenesulfonate in nitrobenzene solvent at 51". From frequency change considerations and force constant model calculations, they concluded that steric interactions yielded the most satisfactory explanation of their results. This implies that the isotope effect is a rate change brought about primarily by a difference between the enthalpies of activation forthe normal and deuterated species, rather than a difference between the entropies of activation. The only temperature dependence study of a secondary deuterium isotope effect on this type of reaction was carried out by Leffek and MacLean (2) who found that the rate change resulting from the deuteration of methyl iodide in its reaction with 2-picoline in benzene was due entirely to an entropy effect. It seemed of interest, therefore, to carry out a temperature dependence study on the isotope effect for N,N-dimethyl-d6-aniline and methyl p-toluenesulfonate.

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