Ab initio MO calculations at the MP2/6-311G** level of theory show
that the thiosulfoxide H2SS is 143
kJ mol-1 less stable than the disulfane HSSH,
separated by an activation barrier of 210 kJ
mol-1. Using much
higher levels of theory, these results are only slighty changed,
proving the suitability of the economical MP2/6-311G** scheme for the present purpose. At the same level
Me2SS is 84 kJ mol-1 less
stable than MeSSMe, with
the transition state lying 340 kJ mol-1 above
MeSSMe. Thermal isomerization of HSSH or MeSSMe can
therefore
be excluded, and H2SS and Me2SS
should be kinetically stable toward unimolecular isomerization at low
temperatures.
Vibrational wavenumbers for H2SS and
Me2SS are given. The allyl methyl thiosulfoxide
MeAllSS is 83 kJ mol-1
less stable than the disulfane MeSSAll, but isomerization of the latter
requires only 110 kJ mol-1. The
corresponding
RSSR and R2SS structures for R = Pr and All have
been calculated at the HF/6-31G* level. The
bimolecular
decomposition of dimethyl thiosulfoxide to dimethyl sulfide and
S2 is exothermic but spin-forbidden in the case
of
triplet S2, and endothermic but spin-allowed when singlet
S2 is formed. The reactions of Me2SS
with sulfur molecules
S
x
(x > 2) to give Me2S
and S
x
+1 are
exothermic.
Ab initio molecular orbital calculations at various,
correlated levels of theory have been performed on eight
isomers of the [H,O4,S2]- anion
and six forms of [H2,O4,S2].
For the former species, the hypothetical
O3SSOH-
(9) ion is identified as the lowest energy isomer using
second-order Møller−Plesset perturbation theory or
the CCSD(T) method, with the protonated dithionite ion,
O2SSO2H- (6),
being only marginally (less than 5
kJ mol-1 at 25 °C) higher in energy.
In contrast, the B3LYP density functional predicts a rather
different
order of relative stabilities, with
O2SSO2H- (6) as
the by far most stable ion. 6 is stable with respect
to
dissociation into SO2 and HOSO
-
or
into SO2
•- and
HOSO• (which is more stable than
HSO2
•). For the
species of composition H2S2O4 the
cagelike dithionous acid molecule
(HO)O2SSO2(OH) (14)
represents the
global minimum at all four levels of theory. However, also for
this species, the relative stabilities predicted
by the B3LYP approach differ considerably from results obtained from
the conventional wave function-based methods. 14 is stabilized by two very strong
intramolecular hydrogen bonds (symmetry C
2).
The
homolytic dissociation of 14 at the SS bond is strongly
endothermic, but the molecule is unstable with respect
to dissociation into H2SO2 and
SO2. The harmonic wavenumbers and infrared intensities
of the fundamental
vibrations of 6 and 14 are given.
High-level a b initio MO calculations have been performed to determine the structures, energies, and vibrational spectra of eight isomers (including rotamers) of H2S20 and five isomershotamen of Me~S20. At the MP2/ 6-3 llG**//MP2/6-311G** level of theory, including the zero-point energies (ZPE), the order of decreasing stability of H2S20 molecules is trans-HOSSH > cis-HOSSH > HOS(S)H > trans-HSS (0)H > cis-HSS(0)H > trans-HSOSH > cis-HSOSH > HS(O)(S)H. The remarkable stability of the thiono derivative HOS(S)H over the sulfoxide HSS(0)H is explained by the stabilization of the former by an intramolecular OH**S hydrogen bond. The dimethyl derivatives of the more stable H2S20 isomers have been calculated at the MP2/6-31 lG**//HF/6-31 lG**+ZPE level. The order of decreasing stability is trans-MeOSSMe > cis-MeOSSMe > cis-MeSS(0)Me > trans-MeSS(0)Me > MeOS(S)Me. The geometrical parameters of these species agree well with those of related compounds, e.g., MeOSSOMe and RSS(0)R with R = p-tolyl.
High-level a b initio MO calculations (MP2/6-31 lG**//MP2/6-31 lG**) on 16 isomeric forms of H,S,O (including rotamers) have been performed. The nonhelical hydroxotrisulfane HOSSSH 1 a (motif + + -) is the most stable isomer, while the chains with motifs + + + and + -+ are less stable by 1.7 and 3.7 kJmol-', respectively. The other isomers of H,S,O increase in energy in the order HSS(0)SH < HOS(S)SH < HSOSSH < HS(0)SSH < HS(S)SOH <
HS(S)OSH.The trisulfane-2-oxide
The preparation of 4,4,4-Trichloro-J 2 -l-butenyl-dichlorophosphate and -dichlorophosphite from the corresponding P(V) and P(III) compounds is described.
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