MICROWAVE-SPECTRUM, CONFORMATIONAL EQUILIBRIUM, INTRAMOLECULAR HYDROGEN-BONDING AND AB-INITIO CALCULATIONS FOR 2-FURANMETHANETHIOL (FURFURYL MERCAPTAN)

The microwave spectra of 2-furanmethanethiol and one deuterated specie s (mercapto group) have been investigated in the 26.0-39.5 GHz spectra l region at - 15-degrees-C. Two conformers denoted Skew 1 and Skew 3 w ere assigned. In Skew 1 the C = C-C-S dihedral angle is about 109-degr ees from syn, while this dihedral angle is approximately 111-degrees f rom syn in Skew 3. These two skew forms are each stabilized by a weak intramolecular hydrogen bond which is formed between the hydrogen atom of the mercapto group and the pi electrons of the furan ring in the c ase of Skew 1, and between the same hydrogen atom and the oxygen atom of the ring in the case of Skew 3. Skew 3 is the most stable rotamer. It is 2.3(5) kJ mol-1 more stable than Skew 1. There is no indication of the stable coexistence of large fractions of further rotamers. The microwave work has been assisted by ab initio computations at the 6-31 G* level of theory.