Jean M. McKenna

Bis-steroids as potential enzyme models: perylene solubilisation and dye spectral changes with aqueous solutions of some derivatives of conessine and cholic acid

Several bis-steroids derived from conessine or cholic acid solubilise perylene into aqueous solution without evidence of micelle formation, and cause spectral changes in aqueous pinacyanol iodide; mono-steroids examined show these effects (characteristic of hydrophobic interaction) only on micellisation or not at all.

Stereochemistry of photosolvolysis of (–)-1-phenylethyltrimethylammonium iodide in water and in methanol, and nucleophile capture ratios during photosolvolysis of some benzylammonium salts

The photosolvolysis of (–)-1-phenylethyltrimethylammonium iodide in water or methanol is characterised by extensive racemisation accompanied by some net configurational inversion, a result similar to that generally observed in thermal solvolysis via ion-pairs at chiral secondary centres. Recovered quaternary salt from the photolysis in water is only slightly if at all racemised, while likewise there is no observable epimerisation at nitrogen in recovered benzylammonium salts following photolysis in methanol of suitable derivatives of camphidine, trans-decahydroquinoline, and 4-phenylpiperidine. A strong preference for formation of the methyl ether rather than the alcohol is exhibited on either photochemical or thermal solvolysis of 1-p-methoxyphenylethyltrimethylammonium iodide in aqueous methanol, but nucleophile capture ratios during photosolvolysis of simple benzyltrimethylammonium salts in this mixed solvent system are much lower.

The mechanism of photolysis of some benzyltrimethylammonium salts in water and in alcohols

Photolysis of a range of benzyltrimethylammonium and 3,5-dimethoxybenzyltrimethylammonium salts in water or methanol at 253.7 nm gave typically benzyl alcohols (or benzyl methyl ethers), toluenes, bibenzyls and isomers, and di- and tri-methylammonium salts. By detailed sensitisation and quenching experiments it was established that, in the photolysis of benzyltrimethylammonium bromide in aqueous t-butyl alcohol, benzyl t-butyl ether, benzyl alcohol, and some toluene were produced by a singlet pathway and bibenzyl by a triplet pathway. A general mechanistic scheme for all the photolyses studied is thus suggested.

The mechanism of photolysis of benzyl halides and benzyl acetate in alcohols

The photolysis of benzyl chloride, bromide, iodide, and acetate, and 3,5-dimethoxybenzyl bromide and acetate in methanol and t-butyl alcohol have been examined, and also 3,5-dimethoxybenzyl chloride in ethanol. Solvolysis products and products derived by non-ionic mechanisms are obtained by either direct photolysis at 254 nm or acetone-sensitised photolysis at 300 nm. The mechanisms of the reactions are discussed.

Photolysis of benzyl halides and benzyl acetate in alcohols

Solvolysis products and products derived by non-ionic mechanisms are obtained by either direct or sensitised photolysis of benzyl halides or benzyl acetate in alcohols; the sensitised solvolysis pathway appears to be facilitated by the solvation energies of ion-pair intermediates in relation to those of precursor radical-pairs.

Selectivity in the electrophilic addition of carbenes and nitrenes to aliphatic sulphides and to 4-t-butylthian

Photogenerated bisalkoxycarbonyl- and diacetyl-carbenes add exclusively equatorially to 4-t-butylthian and exhibit selectivity in competitive additions to mixtures of dimethyl and di-isopropyl sulphides. By contrast ethoxycarbonyl- and p-tolysulphonyl-nitrene give equal proportions of axial and equatorial adducts with the thian, and show no selectivity in competitive reactions with dialkyl sulphides. The results in most or all cases appear to be determined by kinetic control.

Effect of 4-t-butyl and other 4-substituents on rate constants for reactions of 1,1-disubstituted cyclohexanes and piperidines. 4-t-Butyl derivatives as valid reactivity models in the kinetic method of conformational analysis of cyclohexanes

A 4-t-butyl group (or a 4-methyl group) has no effect on the rate constant for ethoxy-exchange in diethyl cyclohexane-1,1-dicarboxylates; a 4-phenyl group, however, increases the rate constant by more than 50%. By contrast, both 4-alkyl and 4-phenyl groups increase the overall rate constants for nucleophilic displacement by thiopholate anion at the benzyl methylene groups in 1-benzylpiperidine benzobromides, a 4-t-butyl group approximately doubling the value. The significance of these results in relation to the validity of the usual kinetic method for conformational analysis of cyclohexanes is discussed.

Stereochemistry of photosolvolysis of quaternary benzylammonium salts in hydroxylic solvents

The photosolvolysis of optically active 1-phenyl-ethyltrimethylammonium iodide in water or methanol is characterised by extensive racemisation acompanied by some net configurational inversion; the quaternary salt recovered from incomplete reaction in water has fully retained configuration at carbon, while analogous retention at nitrogen is observed in similar experiments in methanol with appropriately chosen related salts.

Mechanism of photolysis of benzyltrimethylammonium salts in hydroxylic solvents

Photolysis of benzyltrimethylammonium bromide in aqueous t-butyl alcohol gives benzyl t-butyl ether and some toluene by a singlet pathway with more toluene and bibenzyl by a triplet pathway, in each case via a reactive intermediate geminate pair (or pairs); analogous mechanisms are suggested for photolysis of a range of benzyltrimethylammonium salts in water or methanol.

Secondary deuterium kinetic isotope effects associated with multiple deuteriation of trimethylammonium leaving groups in some E1 and E2 reactions

Large normal (kH/kD > 1) secondary deuterium kinetic isotope effects have been observed in E1 and E2 reactions of some steroidal axial trimethylammonium salts when the leaving groups were partly or fully deuteriated; analogous but much smaller effects have been observed in E2 reactions of 2-phenylethyltrimethyl-ammonium salts.