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.

trans-3-Methoxycyclohexene oxide (II), when treated with ethereal hydrogen chloride, gives the chlorohydrin dl-1α-chloro-2β-hydroxy-3α-methoxycyclohexane (IVa), and the cis oxide III gives dl-1β-chloro-2α-hydroxy-3α-methoxycyclohexane (Va). The point of scission of the oxide ring (remote from the methoxyl) is therefore the same as in other reactions observed by ourselves and others. The reaction of 3-methoxycyclohexene (I) with N-chlorosuccinimide and water at 100° gives three chlorohydrins: dl-1β-chloro-2α-hydroxy-3α-methoxycyclohexane (VI), dl-2β-chloro-1α-hydroxy-3α-methoxycyclohexane (VIa), and dl-2α-chloro-1β-hydroxy-3α-methoxycyclohexene (VIIa) (approximately in the ratio 10:38:50, respectively). Two of the chlorohydrins were solids, and the homogeneity of the liquid isomers was demonstrated in several ways. The structures were proven by the nuclear magnetic resonance spectra of the p-nitrobenzoates, and by chemical methods. The results are of considerable interest with regard to the theory of addition and substitution reactions. There is a close parallel with the results in the bromohydrin series.

An unequivocal proof of structure for the methoxychlorocyclopentanols (I′c–IV′c) was obtained by deetherification with 68% hydrobromic acid at 65–70°, followed by hydrogenolysis with Raney nickel and hydrogen, to the 1,2- and 1,3-cyclopentanediols, in the same manner as the methoxybromocyclohexanols (I–IV) were converted into the 1,2- and 1,3-cyclohexanediols. Hydrogenolysis of the methoxybromocyclohexanols and the methoxychlorocyclopentanols provided stereospeciflc syntheses for the cis- and trans-2- and -3-methoxycy-clohexanols and -cyclopentanols in 80–97% yields. Deetherification of the latter compounds with 68% hydrobromic acid gave the corresponding 1,2- and 1,3-cyclohexanediols and 1,2-cyclopentanediols in 70–90% yields, but only 5–7% yields of the 1,3-cyclopentanediols. For the proof of structure of methoxyhalocyclanols, deetherification should therefore precede, rather than follow, dehalogenation.

The stereoisomeric oxides of 3-methoxycyclopentene (3 and 4) and the four trans-chlorohydrins of the same olefin ( 6 9 ) were prepared by methods resembling those used previously in the cyclohexane system. Structure proofs were more difficult than in the cyclohexanes, but served to illustrate some interesting chemistry. Product ratios in the cleavage of each of the epoxides with hydrogen chloride were used to deduce the probable conformations of the four transition states, by comparing the results with those from the cyclohexane system. An unexpected outcome of the work was the new convincing evidence obtained for the intervention of chloronium ions in the addition of "hypochlorous acid" to the olefin.

Can. J. Chem. 57.2444 ( 1979. Two methods, one more accurate, the other more convenient, were developed by which the dilatometer could be used with concurrent reactions of the second and third order. The more accurate method, employing a dilatometer of high specific surface area and equipped with a stable and responsive thermometer, was used in studying as many as six simultaneous oxirane scissions in acid solution. Interlocking double comparisons were made between cyclohexane and cyclopentane ring systcms, between systems possessing or lacking a methoxyl substituent and between others having the substituent in varying orientations, between charged and uncharged nucleophiles, and between transition states of different degrees of protonation. Searching experimental checks were therefore possible in four main areas: (i) a quantitative dissection of the inductive effect from steric and conformational effects, and from dipole-ion or dipole-dipole interactions with the nucleophile, (if) a quantitative demonstration of three main differences between transition states based on 5-and 6-membered rings, (iii) a proof that .,ytr-1,3-effects in the transition states are very charge dependent, being large and positive with unfavourably arranged dipoles, and small or perhaps negative with favourable arrangements, and (iu) a rejection of certain proposed ion-pair alternatives to the A2 mechanism. On a developpi deux methodes, I'une precise et l'autre plus commode, faisant appel a un dilatomttre pour Ctudier des reactions concurrentes du deuxieme et du troisieme ordre; la methode la plus precise, qui fait appel a un dilatornetre a grande surface specifique equip6 d'un thermometre stable et sensible a Cte utilisee pour etudier jusqu'a 6 reactions de scissions simultanees d'oxiranne en solution acide. On a fait des comparaisons de recouvrement double entre les systemes cyclopentanique et cyclohexanique, entre des systemes avec ou sans substituants methoxyles, entre d'autres systemes portant le substituant dans diverses orientations entre des nucleophiles charges ou non et entre des Ctats de transition a divers degres de protonation. I1 a ete possible de faire des verifications experimentales dans quatre domaines principaux; (i) une dissection quantitative entre I'effet inductif et les effets stCriques et conformationnels ou les interactions dipole-ion ou dipole-dipole avec le nuclCophile, (ii) une demonstration quantitative de trois differences principales entre les Ctats de transition portts par des cycles a 5 et a 6 chainons, (iii),une preuve que les effets syn-1,3, dans les Ctats de transition dependent beaucoup sur la charge; les effets Ctant importants et positifs lorsque les dipoles sont dans un arrangement non favorable et petits ou peut &tre negatifs lorsque les arrangements sont favorables et (iu) un rejet de certaines paires d'ions proposees comme alternative au nitcanisme A2.[Traduit par le journal] Introduction measurement of certain polar effects in a particularly Theories of oxirane scission (1, 2) attempt ex-simpl...