Synthesis, Microwave Spectrum, and Conformational Equilibrium of Propa-1,2-dienethiol (H₂CCCHSH)

Abstract

The first synthesis of the kinetically unstable compound propa-1,2-dienethiol (allenethiol; H2CCCHSH) is reported. Its microwave spectrum has been studied in the 41.5−80 GHz spectral range. The spectra of two rotameric forms have been assigned. The C−C−S−H chain of atoms is synperiplanar (0°) in one of the conformers. This dihedral angle is anticlinal in the second rotamer forming an angle of 140(5)° in the second form. The synperiplanar conformer is found to be 1.0(6) kJ/mol more stable than the anticlinal rotamer. The microwave study has been augmented by quantum chemical calculations at the MP2/aug-cc-pVTZ and B3LYP/6-311++G** levels of theory. The predictions of these two theoretical methods are in excellent agreement with the experimental findings