Microwave and quantum chemical study of propargyl thiocyanate (HC[triple bond]CCH2SC[triple bond]N).
The MW spectrum of propargyl thiocyanate (HC[triple bond]CCH(2)SC[triple bond]N) has been investigated for the first time in the 25-80 GHz spectral region at room temperature or at 0 degrees C. The spectra of the ground vibrational state and of the first excited state of the C-S torsional vibration have been assigned for one conformer. This rotamer, denoted ap, has a symmetry plane (C(s) symmetry) and an antiperiplanar arrangement for the C-C-S-C link of atoms. It has previously been claimed that a conformer that has a synclinal conformation for this chain of atoms is present in the gas in approximately the same concentration as ap (approximately 50% of the gas), but this is not supported by the present experiments, where it is shown that the synclinal rotamer, denoted sc, cannot be present in a concentration exceeding 1/3 of the total. It is therefore concluded that ap must be at least 3.0 kJ/mol more stable than sc. The spectroscopic work has been augmented by quantum chemical calculations at advanced B3LYP/aug-cc-pVQZ, B3LYP/6-311++G(3df,3pd), and MP2/aug-cc-pVTZ levels of theory. These theoretical calculations underestimate the energy difference between ap and sc and predict values for the conformationally important C-C-S-C dihedral angle of the hypothetical synclinal form that deviates by approximately 10 degrees.
Møllendal
Harald
H
Centre for Theoretical and Computational Chemistry (CTCC), Department of Chemistry, University of Oslo, P.O. Box 1033 Blindern, NO-0315 Oslo, Norway. harald.mollendal@kjemi.uio.no
Konovalov
Alexey
A
Guillemin
Jean-Claude
JC
D003198:Computer Simulation; D008872:Microwaves; D008956:Models, Chemical; D010293:Pargyline / Q000031:analogs & derivatives* / Q000737:chemistry*; D011789:Quantum Theory; D013861:Thiocyanates / Q000737:chemistry*
D013861:Thiocyanates; D010293:Pargyline; C031760:thiocyanate