Dennis G. Garratt

The noncumulative effect of methyl substituents on the rate of addition of benzeneselenenyl chloride to olefins

Abstract The rates and products of addition of benzeneselenenyl chloride to ethylene and its six Me substituted derivatives have been determined in methylene chloride at 25°. Unlike the addition of 4-chlorobenzenesulfenyl chloride to this same series of compounds, the effect of Me groups on the rates of addition is not cumulative. Also the regiochemistry of the product is different. For arenesulfenyl chloride additions, products of anti -Markownikoff orientation are formed preferentially under conditions of kinetic control. Under similar conditions regiospecific formation of the Markownikoff adduct is observed for the addition of benzeneselenenyl chloride to methylpropene and 2-methyl-2-butene. These data indicate a difference in both rate and product determining transition states between additions of arenesulfenyl and selenenyl chlorides to alkenes.

A comparison of transition states in nucleophilic displacement by alkenes at bivalent sulfur and selenium

Abstract Evidence is presented that S-Cl bond breaking and C-S bond making are about equal in the transition state of the addition of ArSCl to 1-(4-X-phenyl)propenes while SeCl bond breaking is more advanced than C-Se bond making in the analogous reaction of ArSeCl.

Nucleophilic displacement reactions at Se (II) : Reaction of areneselenenyl chlorides and 2-chloroalkyl phenyl selenides

Abstract The products of the title reaction depend upon the relative concentrations of reactants. With equimolar concentrations or an excess of 2-chloroalkyl phenyl selenide, the products are 1,2-dicloroethane and a diaryldiselenide. When excess areneselenenyl chloride is used ,the products are a diaryl diselenide and 2-chloroalkyl phenyl selenide dichloride. A mechanism involving nucleophilic displacement at selenenyl selenium is proposed to account for the observed products. Structural changes in the selenide or varying substituents in the 4-position of areneselenenyl chloride has little effect on the rate of the reaction. In the proposed continuum of mechanisms of nucleophilic displacement reactions at Se (II), an S N 2-like transition state best accounts for the data.

A molecular orbital study of the stereochemistry and conformational stability of tetra-coordinate selenium in the selenocyclopropane system

Abstract Semiempirical molecular orbital calculations were performed on epi-selenurane (1-chloro-1-methyl-selenocyclopropane), the previously proposed reaction intermediate of the addition of selenenyl chloride to olefin: The geometry optimization suggested that the most stable conformation of episelenurane adduct resembles a distorted trigonal bipyramid in which the three membered ring is in an equatorial-apical orientation. The study has also been extended to substituted ethylenes.

The addition of 4-chlorobenzenesulfenyl chloride to phenyl-substituted acetylenes: the structures of the intermediate thiirenium ion

A comparison is made of the effect on the rates and product compositions of substituting a phenyl ring for a hydrogen on ethylene and acetylene and their derivatives. Such a comparison leads to the...