Spectroscopic characterization and conformational properties of S-(fluoroformyl)-O-(acetyl) thioperoxide, FC(O)SOC(O)CH3 and S-(fluoroformyl)-O-(trifluoroacetyl) thioperoxide, FC(O)SOC(O)CF3

M. CUAQUIRA REINA; C.O. DELLA VÉDOVA; S.E. ULIC; H. WILLNER; H. OBERHAMMER

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY

WILEY-V C H VERLAG GMBH

Año: 2009 vol. - p. 4094 - 4104

1434-1948

The conformational properties of FC(O)SOC(O)CH3 and FC(O)SOC(O)CF3 have been studied by vibrational spectroscopy (IR (gas phase, Ar matrix), Raman (liquid phase)) and quantum chemical calculations (B3LYP and MP2 methods). For both compounds the syn-gauche-syn conformer with synperiplanar orientation of both carbonyl C=O bonds with respect to the S–O bond, and gauche orientation around the S–O bond (C1 symmetry) is the most stable structure (73(5)% for FC(O)SOC(O)CH3 and 82(5)% for FC(O)SOC(O)CF3). For FC(O)SOC(O)CH3 two more conformers are observed in the Ar-matrix spectra, 18(5)% syn-trans-syn with trans orientation around the S–O bond (f(C–S–O–C) = 180°, C2 symmetry) and 9(5)% anti-gauche-syn with the FC(O) group oriented anti with respect to the S–O bond. The experimental free energy differences for these most stable forms of FC(O)SOC(O)CH3 are ÄG° = G°(syn-trans-syn) – G°(syn-gauche-syn) = 0.83(17) kcal mol-1 and ÄG° = G°(anti-gauche-syn) – G°(syn-gauche-syn) = 1.27(35) kcal mol-1, respectively. These values are well reproduced by the B3YLP/aug-cc-pVTZ method (0.76 kcal mol-1 and 1.23 kcal mol-1), but not by the MP2 approximation (2.72 kcal mol-1 and 1.28 kcal mol-1) For FC(O)SOC(O)CF3 only one more stable conformer, 18(5)% anti-gauche-syn, is observed. The experimental free energy difference between both rotamers of FC(O)SOC(O)CF3, ÄG° = G°(anti-gauche-syn) – G°(syn-gauche-syn) = 0.90(17) kcal mol-1, is reproduced very well by the B3YLP/6-311++G** method (0.82 kcal mol-1) and reasonably well by B3LYP/aug-cc-pVTZ (1.17 kcal mol-1) and MP2/6-31G* (1.23 kcal mol-1) calculations.