George H. Schmid

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.

A quantum mechanical study of the photodimerization of anthracene and its derivatives

Abstract Calculations based on the delocalized model of the transition state have been found to be in qualitative accord with the experimental results of the photodimerization of anthracene and its derivatives.

A STANDARD DEFINITION OF THE TERM “THIIRANIUM ION”

Abstract It is proposed that conventional nomenclature, based on that use for carbenium ions, be restored to the naming of thiiranium ions. Such a definition provides a general mechanistic classification for a large number of apparently diverse reactions while still allowing refinements to the mechanism in the form of thiiranium ion-pairs.

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.

The effect of environment on the reactions of thiiranium ions

Abstract The thiiranium ion formed by the reaction of Z -1-phenylpropene and (4-ClC6H4S)2SC6H4ClSbCl6 in CH2Cl9 at −70°C reacts with Cl− to form both erythro - and threo -Markownikoff B-chlorosulfides.

An ab initio study of halogen—olefin molecular complexes

Abstract A systematic computational study, using the 3–21G basis set, of the F 2 C 2 H 4 system shows that several molecular complex configurations can exist and that the axial-perpendicular type is not the most stable. Full geometry optimization results for F 2 C 2 H 4 and Cl 2 C 2 H 4 in axial-perpendicular configurations are reported and shown to be improvements over previous calculations.

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.

Molecular orbital calculations on the C2H4SH+ cation

Systematic non-empirical SCF-MO calculations were carried out on the two limiting structures of C2H4SH+. In both of these cases two different atomic orbital basis sets were used. The results indicate that the open structure (β-thioethyl cation) lacks thermodynamic stability and spontaneously interconverts into the bridged structure (thiiranium ion). The pyramidal inversion at sulphur in the thiiranium ion was computed to be 78.11 kcal mol–1.

Ab initio SCF-MO study of the reaction intermediates formed by addition of thiohypochlorous acid to ethylene

Non-empirical SCF-MO calculations, using two different basis sets, were carried out on a cyclic sulphurane and a thiiranium–chloride ion-pair. The calculated energies indicated that in the gas phase the covalent cyclic sulphurane is favoured over the ionic species. The activation energy for the internal collapse of the cyclic sulphurane to product was calculated to be 42 kcal mol–1, well below the energy of the thiiranium–chloride ion-pair. These results support the suggestion that thiiranium ions prevail in polar solvents but tetracovalent sulphur intermediates are favoured in solvents of low polarity.