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The mode of scission of cis- and trans-3-methoxycyclohexene oxides by hydrogen chloride, hydrogen bromide, ammonia, acetic acid, and methanol (under both acidic and alkaline conditions) has been examined using vapor-phase chromatography to detect and isolate minor isomers. Approximately 10% of the product from opening of the trans oxide is formed by attack at position-2 with each of these nucleophiles, whereas opening of the cis oxide proceeds exclusively by attack at position-1. The results are interpreted as reflecting very similar transition states for all of these reactions, with differences in product distributions for the two oxides being governed by the inductive effect of the methoxyl group and by steric factors in the corresponding transition states.

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. Can. J . Chem. 68, 1837 (1990).The reactions of p-nitrophenyl diphenylphosphinate (1) with lithium, sodium, potassium, and benzyltrimethylammonium phenoxides (BTMAOPh) have been studied by spectrophotometric techniques in anhydrous ethanol at 25°C. The reactivity (kob,) of the alkali metal phenoxides increases in the order BTMAOPh < KOPh < NaOPh < LiOPh. The rate of reaction of 1 with LiOPh is enhanced when lithium salts (LiSCN, LiN03, LiC104, LiOAc) are added to the reaction media. The addition of the alkali metal complexing agents dicyclohexyl-18-crown-6 ether or [2.2.2]cryptand for ~a ' , and [2.l. llcryptand for Li', to each of the alkali metal phenoxide reactions resulted in a decrease in rate, indicating catalysis by the alkali metal ions. The kinetic data are analyzed to obtain specific rate coefficients of reactions of phenoxide and ethoxide as the dissociated ions and as alkali metal -phenoxide ion pairs. Reactivities follow the order kphoM > kPhO-; kEtOM > kEtO-; k E t O > kPhO-; kEtOM > kPhOM.A mechanism is proposed in which the ion-paired metal phenoxide is more reactive towards the substrate than is the dissociated phenoxide. Analysis of the data in terms of initial state and transition state interactions with metal ions indicates that the increased reactivity of the ion-paired species results from greater stabilization of the negatively charged transition state relative to stabilization of the ion-paired nucleophile.Key words: nucleophilic displacement at phosphorus by phenoxide, alkali-metal-ion catalysis. Faisant appel 2 des techniques spectrophotomCtriques et opCrant dans de 1'Cthanol anhydre, A 25"C, on a Ctudie les reactions du diphenylphosphinate de p-nitrophknyle (1) avec les phenolates de lithium, de sodium, de potassium et de benzyltrimkthylammonium (BTMAOPh). La rCactivite (kobs) des phCnolates des mCtaux alcalins augmente dans l'ordre : BTMAOPh < KOPh < NaOPh < LiOPh. Lorsqu'on ajoute des sels de lithium (LiSCN, LiN03, LiC104, LiOAc) au milieu rkactionnel, il y a une augmentation de la vitesse de reaction du composC 1 avec le LiOPh. Lorsqu'on ajoute des agents complexants des mCtaux alcalins, comme 1'Cther dicyclohexyl-18-couronne-6 ou le cryptand[2.2.2] pour le Na' et le cryptand[2.1.1] pour le Lif, A chacune des reactions des phenolates de metaux alcalins, les vitesses de riaction sont abaisskes; ces rksultats indiquent qu'il y a catalyse par les ions des metaux alcalins. On a analyse les donnCes cinktiques pour obtenir les coefficients specifiques des vitesses de rCactions du phenolate et de 1'Cthylate comme ions dissociks ainsi que sous la forme de paires l'ions phenolate-metal alcalin. Les rCactivitCs sont dans l'ordre suivant : kPhoM > kPhO-; kEtOM > kEtO-; kEtO-> kPhO-; kEIOM > kPhOM On propose un mecanisme selon lequel, par rapport 2 chaque substrat, chaque phCnolate existant sous la forme d'une paire d'ions est plus reactif que le phenolate qui n'est pas dissocie. Une analyse des donnkes en fonction de 1'Ctat initial et des interactions avec les ions mktalliques dans 1'Ctat...