+ rnh2ingly, the kobSd at pH 14 are expected to be rather insensitive to substituent effects, while the other a priori conceivable mechanism, addition of water to the ion of the Schiff base, would cause a strong influence of substituents on k(l4). As a matter of fact, the observed values of k( 14) are about the same for all the substituted salicylidenes. If, however, reaction 4 is isolated, the calculated values of k4 depend strongly on the a's as may be seen in Figure 5 (p = 2.85).All the kinetically important reactions, under the experimental conditions where hydrolysis was studied, are depicted in Scheme I.

The rates and products of addition of 4-chlorobenzenesulfenyl chloride to 30 mono- and disubstituted alkenes have been determined in 1,1,2,2-tetrachloroethane at 25 °C. The rates of addition span a range of 106. No correlation with the extended Taft equation was found with the rates of all 30 compounds. The rate ratio kc/kt for addition to nine pairs of isomeric cis-trans alkenes ranges from a low of 3.1 for the 2-butenes to a high of 1.57 × 105 for the 2,2,5,5-tetramethyl-3-hexenes. The rate ratio kc/kt does not always increase regularly with the increasing size of the substituents which suggests that relief of ground state strain is not important in the rate determining transition state. Greater steric hindrance between the electrophile and the trans alkene compared to the cis isomer is proposed to account for the results.

Die spezifischen Geschwindigkeitskonstanten für die Addition des Titelsulfenylchlorids an 30 mono‐ und disubstituierten endständigen oder cistrans‐Alkenen in 1,1,2,2‐Tetrachloräthan bei 25°C werden bestimmt.

. Can. J. Chem. 65, 1172Chem. 65, (1987. The rates and products of addition of 4-chlorobenzenesulfenyl chloride to E-and Z-3-methyl-2-pentene, E-and Z-3,4-dimethyl-2-pentene, E-and Z-3,4,4-trimethyl-2-pentene, and 2,4,4-trimethyl-2-pentene were studied to determine if the mechanism involved a tertiary P arylthio carbocation. It was found that the rates of addition are not as fast as one would predict based on the polar effects of the substituents on the rate of addition to mono-and disubstituted alkenes. The products are formed by anti-stereospecific addition as in the case of addition to 1,2-disubstituted alkenes. As a result it is concluded that the reaction occurs by means of the usual mechanism involving a bridged thiiranium ion. Dans le but de dtterminer si le mtcanisme de la reaction implique un carbocation P-arylthio tertiaire, on a dttermint les vitesses de rtaction ainsi que la nature des produits obtenus lors de l'addition du chlorure de chloro-4 benzknesulfknyle sur les mtthyl-3 pentknes-2 (E ou Z), sur les dimCthy1-3,4 pentknes-2 (E ou Z), sur les trimtthyl-3,4,4 pentknes-2 (E ou Z) et sur le trimtthyl-2,4,4 pentkne. On a trouvt que les vitesses d'addition ne sont pas aussi rapides que celles que l'on pourrait prtvoir en se basant sur les effets polaires des substituants sur les vitesses d'addition sur des alcknes mono-ou disubstituts. Les produits se foment par une addition sttrtosptcifique anti, comme dans les cas des additions sur des alcknes disubstituts en positions 1,2. Sur la base de ces rtsultats, on en conclut que la rtaction se produit par le biais du mtcanisme usuel impliquant un ion thiiranium pontt.[Traduit par la revue]The systematic study of the addition of arenesulfenyl chlorides to alkenes carried out in this laboratory has established many of the mechanistic features of this reaction (1). It is possible to conclude that in this addition reaction the ratedetermining transition state is bridged and there is little charge on either carbon or sulfur (2). Furthermore, in the productdetermining step, attack by chloride ion occurs at the least hindered carbon of the thiiranium ion (3). These results are in contrast to the reactions of stable thiiranium ions, which undergo reactions with nucleophiles at the most hindered carbon atom (4). A possible explanation (5) for this difference in product regiochemistry is that the addition reaction, carried out in relatively nonpolar solvents, occurs by means of a contact ion pair. The reaction of stable thiiranium ions, carried out in highly polar solvents, occurs by means of a dissociated ion.The importance of ion pairs in the mechanism of many reactions in solution is well documented (6). Electrophilic additions are no exception. A number of people have proposed that the mechanism of an electrophilic addition reaction could involve ion-pair intermediates (7). Subsequent work by Rolston and Yates (8) and Gamier and Dubois (9) established the importance of ion pairs in the bromination of alkenes. In 1972, we provided evidence that the mechanism of...

Die Olefine (I) addieren das Sulfenylchlorid (II) zu den Addukten (III) mit anti‐ Markovnikov‐Orientierung (Kinetik), die sich langsam (Halbwertszeit 56 Tage bzw. 2 Monate) zu den Markovnikov‐Addukten (IV) isomerisieren, wobei das Addukt (IVb) auch vom Eliminierungsprodukt (V) begleitet wird.