Collect. Czech. Chem. Commun. 2011, 76, 645-667
Published online 2011-05-03 12:01:21

Do the mercaptocarbene (H–C–S–H) and selenocarbene (H–C–Se–H) congeners of hydroxycarbene (H–C–O–H) undergo 1,2-H-tunneling?

János Sarkaa, Attila G. Császára,* and Peter R. Schreinerb,*

a Laboratory of Molecular Spectroscopy and Department of Physical Chemistry, Institute of Chemistry, Loránd Eötvös University, H-1518 Budapest 112, P.O. Box 32, Hungary
b Institute für Organische Chemie der Justus-Liebig-Universität, Heinrich-Buff-Ring 58, D-35292 Giessen, Germany


The principal purpose of this investigation is the determination of the tunneling half-lives of the trans-HCSH → H2CS and the trans-HCSeH → H2CSe unimolecular isomerization reactions at temperatures close to 0 K. To aid these determinations, accurate electronic structure computations were performed, with electron correlation treatments as extensive as CCSDT(Q) and basis sets as large as aug-cc-pCV5Z, for the isomers of [H,H,C,S] and [H,H,C,Se] on their lowest singlet surfaces and for the appropriate transition states yielding structural data for key stationary points characterizing the isomerization reactions. The computational results were subjected to a focal-point analysis (FPA) that yields accurate relative energies with uncertainty estimates. The tunneling half-lives were determined by a simple Eckart-barrier approach and via the more sophisticated though still one-dimensional Wentzel–Kramers–Brillouin (WKB) approximation. Only stationary-point information is needed for the former while an intrinsic reaction path (IRP) is necessary for the latter approach. Both protocols suggest that, unlike for the parent hydroxymethylene (HCOH), at the low temperatures of matrix isolation experiments no tunneling will be observable for the trans-HCSH and trans-HCSeH systems.

Keywords: Carbenes; Mercaptocarbene (HCSH); Selenocarbene (HCSeH); Tunneling; Eckart barrier; WKB approximation; Ab initio calculations; Hydrogen transfer.

References: 89 live references.