Hyperconjugation and the increasing bulk of OCOCX3 substituents in trans-1,4-disubstituted cyclohexanes destabilize the diequatorial conformer.

The trans diesters of 1,4-cyclohexanediol with a number of acetic acid analogues, CX3COOH, of varying steric hindrance and polarity (CX3 = Me, Et, iso-Pr, tert-Bu, CF3, CH2Cl, CHCl2, CCl3, CH2Br, CHBr2, CBr3) were synthesized, and the axial,axial/equatorial,equatorial conformational equilibria were studied by low-temperature 1H NMR spectroscopy in CD2Cl2. The structures and relative energies of the axial,axial and equatorial,equatorial conformers were calculated at both the MP2/6-311G* and the MP2/6-311+G* levels of theory, and it was only by including diffuse functions that a good correlation of deltaG(o)calcd vs deltaG(o)exptl could be obtained. Both the structures and the energy differences of the axial,axial and equatorial,equatorial conformers are discussed with respect to the established models of conformational analysis, viz.

Formation and cleavage of aromatic disulfide radical anions.

The electron transfer (ET) to a series of para-substituted diaryl disulfides, having the general formula (X-C(6)H(4)S-)(2), has been studied. The X groups were selected as to have a comprehensive variation of the substituent effect, being X = NH(2), MeO, H, F, Cl, CO(2)Et, CN, and NO(2). The reduction was carried out experimentally, using N,N-dimethylformamide as the solvent, and by molecular orbital (MO) ab initio calculations.

Electronic and steric substituent influences on the conformational equilibria of cyclohexyl esters: the anomeric effect is not anomalous!

The cyclohexyl esters of a series of carboxylic acids, RCO(2)H, spanning a range of electronegativities and quotients of steric hindrance for the R substituent (R=Me, Et, iPr, tBu, CF(3), CH(2)Cl, CHCl(2), CCl(3), CH(2)Br, CHBr(2), and CBr(3)) were prepared. Their conformational equilibria in CD(2)Cl(2) were examined by low-temperature (1)H NMR spectroscopy to study the axial or equatorial orientation of the ester functionality with respect to the adopted chair conformation of the cyclohexane ring. The ab initio and DFT geometry-optimized structures and relative free energies of the axial and equatorial conformers were also calculated at the HF/6-311G**, MP2/6-311G**, and B3LYP/6-31G** levels of theory, both in the gas phase and in solution.

Insights into the free-energy dependence of intramolecular dissociative electron transfers.

To study the relationship between rate and driving force of intramolecular dissociative electron transfers, a series of donor-spacer-acceptor (D-Sp-A) systems has been devised and synthesized. cis-1,4-Cyclohexanedyil and a perester functional group were kept constant as the spacer and acceptor, respectively. By changing the aryl substituents of the phthalimide moiety, which served as the donor, the driving force could be varied by 0.

Theoretical and electrochemical analysis of dissociative electron transfers proceeding through formation of loose radical anion species: reduction of symmetrical and unsymmetrical disulfides.

The dissociative reduction of a series of symmetrical (RSSR, R = H, Me, t-Bu, Ph) and unsymmetrical disulfides (RSSR', R = H, R' = Me and R = Ph, R' = Me, t-Bu) was studied theoretically, by MO ab initio calculations and, for five of them, also experimentally, by convolution voltammetry in N,N-dimethylformamide. The reduction is dissociative but proceeds by a stepwise mechanism entailing the formation of the radical anion species. The electrochemical data led to estimated large intrinsic barriers, in agreement with an unusually large structural modification undergone by the disulfide molecules upon electron transfer.

Ab-Initio MO Study of the Peracid Oxidation of Dimethyl Thiosulfinate.

The mechanism of oxidation of dimethyl thiosulfinate with performic acid was investigated theoretically at MO ab-initio level. Equilibrium geometries and transition states were optimized with two different basis sets (3-21G and 6-31G) and the inclusion of dynamic correlation correction at MP2 level. Along the possible reactions paths three different transition states were characterized, namely, those leading to the formation of the diastereomeric forms (RR/SS or RS/SR) of alpha-disulfoxide and that leading to the thiosulfonate.