Raimo Keskinen

Properties and reactions of 1,3-oxathiolanes—III : Conformational energies and the most probable conformations of 2-alkyl-5-methyl- and 2,2-dialkyl-5-methyl-1,3-oxathiolanes

Abstract Several 2-alkyl-5-methyl- and 2,2-dialkyl-5-methyl-1,3-oxathiolanes have been prepared and their conformational properties clarified through acid-catalysed equilibration of diastereoisomers and with the aid of 1 H NMR spectroscopy. The collected data suggests a moderately flexible 5-membered ring which, however, shows several features of specific interactions and favoured conformations.

Properties and reactions of 1,3-oxathiolans. Part IV. Conformational analysis of 2-alkyl-4-methyl- and 2-alkyl-2,4-dimethyl-1,3-oxathiolans with the aid of 1H nuclear magnetic resonance spectroscopy and chemical equilibration

Several 2-alkyl-4-methyl- and 2-alkyl-2,4-dimethyl-1,3-oxathiolans have been prepared and their conformational properties clarified by examination of acid-catalysed equilibrations of diastereoisomers and with the aid of 100 and 220 MHz 1H n.m.r. spectroscopy. The data accord best with a moderately flexible envelope conformation which shows certain characteristic features.

Properties and reactions of 1,3-oxathiolans. Part 6. Chemical equilibration and 1H nuclear magnetic resonance conformational study of 4,5-dimethyl-, 2,4,5-trimethyl-, and 2,2,4,5- and 2,4,4,5-tetramethyl-1,3-oxathiolans

The 60 MHz 1H n.m.r. spectra of nine differently substituted 4,5-dimethyl-1,3-oxathiolans have been recorded and analysed. The n.m.r. data are compared with those previously reported for the 4-methyl- and 5-methyl-1,3-oxa-thiolans. Epimeric derivatives were chemically equilibrated to determine the energy differences between the diastereoisomers in question. The thermodynamic quantities obtained were used to clarify different spatial interactions in these compounds.

Conformational analysis. Part VII. 2-Alkyl-4-methyl- and 2-alkyl-2,4-dimethyl-1,3-dithiolans

2-Alkyl-4-methyl- and 2-alkyl-2,4-dimethyl-1,3-dithiolans have been prepared and studied by means of the acid-cataysed equilibration of the diastereoisomers and 1H n.m.r. spectroscopy. Free energy differences between diastereoisomers are small and within the range 0·13–0·54 kJ mol–1 for the dialkyl series and 0·71–1·00 kJ mol–1 for the trialkyl series. The data suggest that the dithiolan ring is quite a flexible system and a possible minium energy conformation can be defined only if there is a bulky substituent at the 2-position.

Nuclear magnetic resonance studies on the conformational, effects of alkyl-substituted 1,3-oxathiolanes 1–3

Abstract The 1 H NMR spectra of a number of alkyl-substituted 1,3-oxathiolanes were recorded and analysed. The NMR data were employed to predict the configurations and most probable conformations of the 1,3-oxathiolane ring and also to estimate the conformational free energy values of the pseudoaxial substituents in the different positions. Some of the compounds studied were epimeric and able to equilibrate. The energy parameters obtained from chemical shifts and vicinal coupling constants were found to be in excellent agreement with the results derived from equilibration experiments.