Does the Carbon-Sulfur triple bond exist? There’s probably little doubt it does in the CS molecule. But now Schreiner and Mloston have offered up the H-C≡S-OH species as a possibility.1 Obtained by flash photolysis of 1, giving 2, and upon irradiation at 254 nm, H-C≡S-OH 3 is the observed species and not the expected carbene HO-C-SH 4. 3 is confirmed by excellent agreement between the observed and computationally predicted IR spectra.
The CCSD(T)/cc-pVTZ structures of 3 and 4 are shown in Figure 1. It is interesting that the carbene is not observed, even though it is 26.6 kcal mol-1 more stable than 3.
Figure 1. CCSD(T)/cc-PVTZ optimized structures of 3 and 4.1
So is there a triple bond? The short C-S distance (1.547 Å) is very similar to that in CS (1.545 Å). NBO analysis indicates a triple bond. But the MOs indicate significant lone pair build-up on both C and S, consistent with the strongly non-linear angles about these two atoms. The authors conclude that 3 is a “structure with a rather strong CS double bond or a weak triple bond”.
(1) Schreiner, P. R.; Reisenauer, H. P.; Romanski, J.; Mloston, G., "A Formal Carbon-Sulfur Triple Bond: H-C≡S-O-H," Angew. Chem. Int. Ed., 2009, 48, 8133-8136, DOI: 10.1002/anie.200903969