Thermochemistry of 1,3-dithiacyclohexane 1-oxide (1,3-dithiane sulfoxide): calorimetric and computational study.
The enthalpies of combustion and sublimation of 1,3-dithiacyclohexane 1-oxide (1,3-dithiane sulfoxide, 2) were measured by a rotating-bomb combustion calorimeter and the Knudsen effusion technique, and the gas-phase enthalpy of formation was determined, DeltafH degrees m(g) = -98.0 +/- 1.9 kJ mol(-1). This value is not as large (negative) as could have been expected from comparison with thermochemical data available for the thiane/thiane oxide reference system. High-level ab initio molecular orbital calculations at the MP2(FULL)/6-31G(3df,2p) level were performed, and the optimized molecular and electronic structures of 2 afforded valuable information on (1) the relative conformational energies of 2-axial and 2-equatorial--the latter being 7.1 kJ mol(-1) more stable than 2-axial, (2) the possible involvement of nS --> sigma*(C-S(O)) hyperconjugation in 2-equatorial, (3) the lack of computational evidence for sigma(S-C) --> sigma*(S-O) stereoelectronic interaction in 2-equatorial, and (4) the relevance of a repulsive electrostatic interaction between sulfur atoms in 1,3-dithiane sulfoxide, which apparently counterbalances any nS --> sigma*(C-S(O)) stabilizing hyperconjugative interaction and accounts for the lower than expected enthalpy of formation for sulfoxide 2.
Roux
María Victoria
MV
Instituto de Química Física "Rocasolano", CSIC, Serrano 119, 28006 Madrid, Spain. victoriaroux@iqfr.csic.es
Temprado
Manuel
M
Jiménez
Pilar
P
Dávalos
Juan Z
JZ
Notario
Rafael
R
Martín-Valcárcel
Gloria
G
Garrido
Leoncio
L
Guzmán-Mejía
Ramón
R
Juaristi
Eusebio
E