Molecular
structure of benzene
sulfonic acid wa
s studied by ga
s-pha
se electron diffraction and quantum chemical (B3LYP/cc-pVTZ, §®§²2/cc-pVDZ, §®§²2/cc-pVTZ) method
s. On the ba
se of ma
ss spectrometric analy
si
s it wa
s found that
saturated vapor at
§´ = 396(9) K i
s repre
sented by only molecular
specie
s, monomeric benzene
sulfonic acid. Theoretical calculation
s showed that the molecule ha
s two mirror conformer
s of
C<
sub>1
sub>
symmetry which can invert to each other via tran
sition
state of
C<sub>ssub> symmetry by rotation of OH-group around SO(H) bond. Both computational method
s, B3LYP and MP2, re
sulted in the
same
structure of enantiomer
s; the MP2/cc-pVDZ calculation
s denoted a over-barrier tran
sition between enantiomer
s at the temperature of electron diffraction experiment, while B3LYP and MP2 calculation
s with cc-pVTZ ba
si
s set e
stimated the barrier height to be comparable with the thermal energy value. Two geometric model
s of
C<
sub>1
sub> and
C<sub>ssub> symmetry were examined in ga
s electron diffraction
structural analy
si
s. It wa
s e
stabli
shed that the
structure of
C<
sub>1
sub>
symmetry (
R<sub>fsub> = 3.3 % ) demon
strated the be
st fit with GED data in compari
son with
C<sub>ssub> structure (
R<sub>fsub> = 3.8 % ).
In conformer of C<sub>1sub> symmetry an ordinary bond SO(§¯) is located almost orthogonal to benzene ring plane, and an OH bond practically eclipses one of SO bonds of SO<sub>3sub>H fragment. The following internuclear distances (?) in benzenesulfonic acid were determined: r<sub>hsub><sub>1sub>(CH)<sub>avsub> = 1.116(6), r<sub>hsub><sub>1sub>(CC)<sub>§ã§âsub> = 1.402(4), r<sub>hsub><sub>1sub>(CS) = 1.770(5), r<sub>hsub><sub>1sub>(SO)<sub>avsub> = 1.438(4), r<sub>hsub><sub>1sub>(SO) = 1.623(4), r<sub>hsub><sub>1sub>(OH) = 0.870(17).
Calculations of internal rotation potential functions and NBO-analysis of electron density distribution in a conformer and transition states between enantiomers were performed to establish the reasons of stability of the found asymmetric structure of the studied molecule. The structure of free molecule of benzenesulfonic acid was compared with that of molecular form in crystal.