Calorimetric and computational study of 1,3-and 1,4-oxathiane sulfones

Article abstract of DOI:10.1021/jo0618472

(Chemical Equation Presented) The enthalpies of formation in the condensed and gas states, Δ_fH°_m(cd) and Δ_fH°_m(g), of 1,3- and 1,4-oxathiane sulfones were derived from their respective enthalpies of combustion in oxygen, measured by a rotating bomb calorimeter and the variation of vapor pressures with temperatures determined by the Knudsen effusion technique. Standard ab initio molecular orbital calculations at the G2(MP2) and G3 levels were performed, and a theoretical study on molecular and electronic structure of the compounds has been carried out. Calculated Δ_fH°_m(g) values at the G3 level using atomization reactions agree well with the experimental ones. These experimental and theoretical studies support that the destabilization found in 1,3-oxathiane sulfone, 11.2 kJ mol^-1 respecting to 1,4-oxathiane sulfone, is due to the electrostatic repulsion between the negative charges of the axial oxygen of the sulfone and the oxygen of the ring and apparently masks any stabilization originating from the hyperconjugative n_O → σ*_C-SO2 stereoelectronic interaction.

Full text of DOI:10.1021/jo0618472

Calorimetric and Computational Study of 1,3-
and 1,4-Oxathiane Sulfones
Mar´ıa Victoria Roux,*,† Manuel Temprado,† Pilar Jime´nez,† Rafael Notario,*,†
Ramo´n Guzma´n-Mej´ıa,‡ and Eusebio Juaristi*,‡
Instituto de Qu´ımica F´ısica “Rocasolano”, CSIC, Serrano 119, 28006 Madrid, Spain, and Departamento
de Qu´ımica, Centro de InVestigacio´n y de Estudios AVanzados del IPN, Apartado Postal 14-740,
07000 Me´xico D.F., Me´xico
Victoriaroux@iqfr.csic.es
ReceiVed September 7, 2006
The enthalpies of formation in the condensed and gas states, ∆fH°m(cd) and ∆fH°m(g), of 1,3- and 1,4-
oxathiane sulfones were derived from their respective enthalpies of combustion in oxygen, measured by
a rotating bomb calorimeter and the variation of vapor pressures with temperatures determined by the
Knudsen effusion technique. Standard ab initio molecular orbital calculations at the G2(MP2) and G3
levels were performed, and a theoretical study on molecular and electronic structure of the compounds
has been carried out. Calculated ∆fH°m(g) values at the G3 level using atomization reactions agree well
with the experimental ones. These experimental and theoretical studies support that the destabilization
found in 1,3-oxathiane sulfone, 11.2 kJ mol-1 respecting to 1,4-oxathiane sulfone, is due to the electrostatic
repulsion between the negative charges of the axial oxygen of the sulfone and the oxygen of the ring and
apparently masks any stabilization originating from the hyperconjugative nO f σ*C-SO stereoelectronic
2
interaction.
Introduction
in the gas state.4 Comparison of the enthalpy of formation of
1,3-dithiane sulfone and 1,4-dithiane sulfone shows the 1,3-
isomer to be 6.7 kJ mol-1 less stable, probably due to diminished
electrostatic repulsion between the positively charged sulfur
heteroatoms in 1,4-dithiane sulfone 34 (Figure 1).
Thermodynamic data such as the enthalpy of formation,
symbolized as ∆fH°m, offer a powerful tool for the understanding
of the relative importance of steric, electrostatic, and stereo-
electronic interactions that are responsible for the contrasting
structural, conformational, and reactivity trends exhibited by
oxygen- and sulfur-containing six-membered heterocycles.1 In
this regard, comparison of the enthalpies of formation of
isomeric compounds is particularly useful because it exhibits
their relative stability, as a consequence of the stabilizing and/
or repulsive interactions of interest.
In this context, the determination of the enthalpy of formation
for 1,3-oxathiane sulfone 4 and 1,4-oxathiane sulfone 5 was
deemed of interest. In particular, a relevant question is whether
a hyperconjugative nO f σ*C-SO interaction will be operative
2
in the 1,3-oxathiane sulfone 4. Indeed, the highly electronegative
SO2 sulfonyl group should lead to a low-energy σ*C-SO orbital
2
with good accepting properties (Figure 2).
Recently, we reported the enthalpies of formation of thiane
sulfone 1,2 1,3-dithiane sulfone 2,3 and 1,4-dithiane sulfone 3
Results
Experimental Determination of the Enthalpy of Formation
in the Gas Phase. The enthalpy of formation in the gas state
of 1,3- and 1,4-oxathiane sulfone, ∆fH°m(g), was determined
from the experimental values of the standard enthalpy of
† Instituto de Qu´ımica F´ısica “Rocasolano”, CSIC.
‡ Centro de Investigacio´n y de Estudios Avanzados del IPN.
(1) Juaristi, E.; Notario, R.; Roux, M. V. Chem. Soc. ReV. 2005, 34,
347.
(2) Roux, M. V.; Temprado, M.; Jime´nez, P.; Da´valos, J. Z.; Notario,
R.; Guzma´n-Mej´ıa, R.; Juaristi, E. J. Org. Chem. 2003, 68, 1762.
(3) Roux, M. V.; Temprado, M.; Jime´nez, P.; Notario, R.; Guzma´n-Mej´ıa,
R.; Juaristi, E. J. Org. Chem. 2004, 69, 1670.
(4) Roux, M. V.; Temprado, M.; Jime´nez, P.; Notario, R.; Guzma´n-Mej´ıa,
R.; Juaristi, E. J. Org. Chem. 2006, 71, 2581.
10.1021/jo0618472 CCC: $37.00 © 2007 American Chemical Society
Published on Web 01/17/2007
J. Org. Chem. 2007, 72, 1143-1147
1143

Roux et al.
FIGURE 1. Differences in the enthalpy of formation (∆∆fH°m, in kJ mol-1) for 1,3-dithiane sulfone 2 and 1,4-dithiane sulfone 3.4
3, and the corresponding bond distances and angles are presented
in Figure 4. The optimized geometries agree well with those
experimentally obtained for both derivatives as it is presented
in the Supporting Information (Table S5).
The most stable forms are the chair conformations, belonging
to the symmetry point groups C1 and Cs for 1,3- and 1,4-
oxathiane sulfones, respectively. The chair structures are similar
to that of cyclohexane but are more puckered to accommodate
the bond angles and bond lengths characteristic for sulfur and
oxygen.
The twist conformers are also minima of the potential energy
surface, but calculations at the HF/6-31G(d) level indicate that
they are between 12.5 and 18.5 kJ mol-1 and between 29.0 and
32.0 kJ mol-1 higher in energy than the respective chair
conformers, for 1,3- and 1,4-oxathiane sulfone, respectively. The
boat conformers are saddle points of first order, corresponding
to transition states in the potential energy surfaces.
FIGURE 2. 1,3-Oxathiane sulfone 4 might benefit from nO f σ*C-SO
2
hyperconjugation (see text).
formation in the crystalline state, ∆fH°m(cr), and the standard
enthalpy of sublimation, ∆subH°m, both referenced to T )
298.15 K.
For sulfones, the length of the SdO bonds is the most
important structural parameter. The sulfonyl group also has the
bond angle OSO and the corresponding O‚‚‚O nonbonded
distance as important structural parameters. Comparison of the
structures of oxathiane sulfones with that calculated for thiane
sulfone shows that the OSO angles are larger (see Figure 4)
and the nonbonded O‚‚‚O distances are shorter (2.51 and 2.50
Å in 1,3- and 1,4-oxathiane sulfones vs 2.56 Å in thiane
sulfone).
The experimental value for the enthalpy of formation in the
crystalline state was determined from combustion calorimetry
experiments. The detailed results for the combustion experiments
of each compound obtained according to references 5 and 6
are presented in the Supporting Information (Tables S2 and S3).
The enthalpy of sublimation, ∆subH°m, was obtained from vapor
pressure measurements by the Knudsen effusion technique. The
detailed results for all the experiments are presented in the
Supporting Information (Table S4).
We can also compare the calculated structures of oxathiane
sulfones with that calculated for oxathianes (see Figure 4). The
CSC angle increases in all the cases when the SO2 group is
present in the molecule. This behavior has been observed in
other compounds. The bond angle XSX always increases when
going from sulfide to sulfone.9
It has been observed10,11 that the introduction of a sulfur
heteroatom into a six-membered carbon ring increases the ring
puckering in comparison with the conformation of cyclohexane.
To measure this ring puckering, we can calculate the average
valency and torsional angles, Θ and Φ, respectively.12 The
average torsional angle, Φ, which is determined by a delicate
balance among valency, torsional, and nonbonded forces, is an
Table 1 collects the values determined for the standard molar
energy of combustion, ∆cU°m, and the standard molar enthalpy
of combustion, ∆cH°m, sublimation, ∆subH°m, and formation in
the crystalline, ∆fH°m(cr), and gaseous states, ∆fH°m(g), for both
sulfones.
No experimental results for the energies and enthalpies of
combustion, sublimation, and formation have been found in the
literature for comparison with our results.
Molecular and Electronic Structures. To our knowledge,
the molecular structures of oxathiane sulfones have not been
studied previously, but the structures of two derivatives of them,
2-methyl-1,3-oxathiane sulfone7 and 3,5-dimethoxy-1,4-ox-
athiane sulfone,8 have been obtained by X-ray diffraction. The
optimized geometries of 1,3- and 1,4-oxathiane sulfones at the
MP2(full)/6-31G(3df,2p) level of theory are presented in Figure
(8) Estrada, M. D.; Lo´pez-Castro, A. Acta Crystallogr., Sect. C: Cryst.
Struct. Commun. 1991, 47, 1030.
(5) Hubbard, W. N.; Scott, D. W.; Waddington, G. Experimental
Thermochemistry; Rossini, F. D., Ed.; Interscience: New York, 1967;
Chapter 5.
(6) Westrum, E. F., Jr. Combustion Calorimetry; Sunner, S.; Ma˘nsson,
M., Eds.; Pergamon Press: Oxford, 1979; Chapter 7
(7) Pihlaja, K.; Sillanpa¨a¨, R.; Dahlqvist, M.; Sta´jer, G.; Ahlgren, M.
Struct. Chem. 1993, 4, 203.
(9) Hargittai, I. In The Chemistry of Sulphones and Sulphoxides; Patai,
S., Rappoport, Z., Stirling, C. J. M., Eds.; Wiley: New York, 1988; pp
33-53.
(10) Hargittai, I. The Structure of Volatile Sulphur Compounds; Aka-
de´miae Kiado´: Budapest and Reidel, Dordrecht, 1985.
(11) Adams, W. D.; Bartell, L. S. J. Mol. Struct. 1977, 37, 261.
(12) Geise, H. J.; Altona, C.; Romers, C. Tetrahedron 1967, 23, 439.
1144 J. Org. Chem., Vol. 72, No. 4, 2007

Study of 1,3- and 1,4-Oxathiane Sulfones
TABLE 1. Experimentally Determined Thermodynamic Magnitudes at the Temperature T ) 298.15 K for 1,3- and 1,4-Oxathiane Sulfonea
∆cU°m
∆cH°m
∆fH°m(cr)
∆
subH°m
∆fH°m(g)
1,3-oxathiane sulfone
1,4-oxathiane sulfone
-2752.9 ( 1.7
-2741.8 ( 1.4
-2757.8 ( 1.7
-2746.8 ( 1.4
-561.5 ( 1.8
-572.6 ( 1.5
92.1 ( 0.7
92.0 ( 1.0
-469.4 ( 1.9
-480.6 ( 1.8
a
All values in kJ mol-1
.
Theoretical Enthalpies of Formation. G2(MP2) and G3
calculated energies at 0 K and enthalpies at 298.15 K, for 1,3-
and 1,4-oxathiane sulfones, are given in Table 2.
In standard Gaussian-n theories, theoretical enthalpies of
formation are calculated through atomization reactions. We have
detailed this method in previous studies.13,14 Raghavachari et
al.15 have proposed to use a standard set of isodesmic reactions,
the “bond separation reaction”,16 where all formal bonds
between nonhydrogen atoms are separated into the simplest
parent molecules containing these same kinds of linkages, to
derive the theoretical enthalpies of formation. However, this
method is not applicable in the case of the compounds studied
because the bond separation isodesmic reaction for 1,3- and 1,4-
oxathiane sulfones, C4H8O3S, is
C4H8O3S(g) + 4CH4(g) + H2O(g) + 2H2S(g) f 2CH3CH3
(g) + 2CH3OH(g) + 2CH3SH(g) + H2SO2(g) (1)
and the experimental enthalpy of formation of one of the
reference compounds, H2SO2, is not available.
We have used in this work an isodesmic reaction using as a
reference (CH3)2SO2:
FIGURE 3. Optimized geometries at the MP2(full)/6-31G(3df,2p) level
for 1,3-oxathiane sulfone 4 and 1,4-oxathiane sulfone 5.
C4H8O3S(g) + 4CH4(g) + H2O(g) f 2CH3CH3(g) +
2CH3OH(g) + (CH3)2SO2(g) (2)
The calculated values for the enthalpies of formation of 1,3-
and 1,4-oxathiane sulfones, at the G2(MP2) and G3 levels of
theory, using atomization and isodesmic reactions,17 are shown
in Table 3. The ∆fH°m value obtained from atomization reaction
at the G2(MP2) level has been modified adding spin-orbit and
bond additivity (BAC) corrections.18 The method has been
detailed in a previous study.19
As can be seen in Table 3, the best theoretical values are
those obtained at the G3 level of theory using atomization
reactions, in very good agreement with the experimental ones.
The calculated difference between the enthalpies of formation
(13) Notario, R.; Castan˜o, O.; Abboud, J.-L. M.; Gomperts, R.; Frutos,
L. M.; Palmeiro, R. J. Org. Chem. 1999, 64, 9011.
(14) Notario, R.; Castan˜o, O.; Gomperts, R.; Frutos, L. M.; Palmeiro,
R. J. Org. Chem. 2000, 65, 4298.
(15) Raghavachari, K.; Stefanov, B. B.; Curtiss, L. A. J. Chem. Phys.
1997, 106, 6764.
FIGURE 4. Optimized structures for thiane 6, 1,3-oxathiane 7, 1,4-
oxathiane 8, and their corresponding sulfones 1, 4, and 5 calculated at
the MP2(full)/6-31G(3df,2p) level of theory. Bond distances are in
Ångstroms, and angles (italic) are in degrees.
(16) Hehre, W. J.; Radom. L.; Schleyer, P. v. R.; Pople, J. A. Ab Initio
Molecular Orbital Theory; Wiley: New York, 1986.
(17) Experimental ∆fH°m values for the reference compounds used in
isodesmic reactions, methane and ethane, -74.6 and -84.0 kJ mol-1
,
easily calculated2 and convenient index of the puckering in six-
membered rings.
respectively, have been taken from: (a) Manion, J. A. J. Phys. Chem. Ref.
Data 2002, 31, 123. ∆fH°m values for methanol and dimethyl sulfone,
-201.5 and -373.1 kJ mol-1, respectively, have been taken from: (b)
Pedley, J. B. Thermochemical Data and Structures of Organic Compounds;
TRC Data Series, TRC: Texas, 1994; Vol. 1. And the ∆fH°m value for
water, -241.8 kJ mol-1, has been taken from: (c) NIST-JANAF Thermo-
chemical Tables, 4th ed.; Chase, M. W., Jr. J. Phys. Chem. Ref. Data 1998,
Monograph 9, 1.
The Φ torsional angles of 1,3- and 1,4-oxathiane sulfones,
60.7° and 61.2°, respectively, have values similar to those
calculated for 1,3-oxathiane (Φ ) 60.9°) and 1,4-oxathiane (Φ
) 60.7°), indicating that all the rings are similarly puckered.
The presence of the O atom in the ring logically increases the
puckering compared to that of thiane sulfone (Φ ) 59.7°) but
decreases the puckering compared to that of 1,3- and 1,4-dithiane
sulfones, 62.3° and 63.0°, respectively.
(18) Petersson, G. A.; Malick, D. K.; Wilson, W. G.; Ochterski, J. W.;
Montgomery, J. A., Jr.; Frisch, M. J. J. Chem. Phys. 1998, 109, 10570.
(19) Roux, M. V.; Jime´nez, P.; Da´valos, J. Z.; Notario, R.; Juaristi, E.
J. Org. Chem. 2001, 66, 5343.
J. Org. Chem, Vol. 72, No. 4, 2007 1145

Roux et al.
TABLE 2. G2(MP2) and G3 Calculated Energies at 0 K and Enthalpies at 298.15 K, for the Oxathiane Sulfones Studieda
G2(MP2) G3
compound
E0
H298
E0
H298
1,3-oxathiane sulfone, 4
1,4-oxathiane sulfone, 5
-780.015773
-780.022073
-780.007379
-780.013743
-780.667113
-780.673254
-780.658719
-780.664924
a
All Values in Hartrees.
TABLE 3. G2(MP2) and G3 Calculated Enthalpies of Formation for the Oxathiane Sulfones Studied from Atomization and the Isodesmic
Reaction (eq 2)a
G2(MP2)
G3
compound
atomization
isodesmic
atomization
isodesmic
experimental
1,3-oxathiane sulfone, 4
1,4-oxathiane sulfone, 5
-475.0
-491.7
-477.5
-494.2
-468.5
-484.8
-479.9
-496.2
-469.4 ( 1.9
-480.6 ( 1.8
a
All values in kJ mol-1
.
of the two oxathiane sulfones studied is 16.6 and 16.3 kJ mol-1
,
at the G2(MP2) and G3 levels, respectively, in good agreement
with the experimental difference, 11.2 kJ mol-1
.
Discussion
The precise structural parameters calculated at the MP2(full)/
6-31G(3df,2p) level for thiane 6, 1,3-oxathiane 7, 1,4-oxathiane
8, and their corresponding sulfones 1, 4, and 5 (Figure 4) are
in line with expectations based on nO f σ*C-SO hyperconju-
2
gation in 1,3-oxathiane sulfone 4. In particular, it can be
appreciated that the C-SO2 bond distance decreases ca. 0.03
Å in going from thiane 6 to its sulfone derivative 1, and this
finding may be ascribed to bond shortening as consequence of
the increased electronegativity of the sulfonyl group relative to
sulfur in the thioether. It is observed that, as expected, the
C-SO2 bond length also decreases ca. 0.03 Å in going from
1,4-oxathiane 8 to the corresponding sulfone 5. By contrast,
the C-SO2 bond length changes little (only ca. -0.01 Å) in
going from 1,3-oxathiane 7 to its corresponding sulfone 4
(Figure 4). The observed reduced shortening in 1,3-oxathiane
sulfone 4 may be explained in terms of the participation of a
double bond-no bond canonical structure, as indicated in
Figure 2.20
This interpretation seems to be supported by NBO charge
calculations (Figure 5). The calculated charge at sulfur is
consistent at +2.46 to +2.47 for sulfones 1, 2, 3, and 5, but a
smaller charge of +2.43 is seen in 1,3-oxathiane sulfone 4, again
in line with participation of the double bond-no bond canonical
structure (Figure 2) that places some negative charge at the
sulfonyl group. Although admittedly small, this charge differ-
ence of 0.03 appears reliable when one considers that all other
sulfones studied in this project (thiane sulfone 1, 1,3-dithiane
sulfone 2, 1,4-dithiane sulfone 3, and 1,4-oxathiane sulfone 5),
where the nX f SO2 stereoelectronic interaction is not antici-
pated, consistently afford a calculated charge of +2.46 to +2.47.
Furthermore, a 0.03 charge difference may be significant upon
consideration that the double bond-no bond canonical form
corresponding to electron transfer is expected to contribute to
only a small degree (no more than 5%).
FIGURE 5. NBO positive charges at sulfur calculated from the
optimized structures of thiane sulfone 1, 1,3-dithiane sulfone 2, 1,4-
dithiane sulfone 3, 1,3-oxathiane sulfone 4, and 1,4-oxathiane sulfone
5 at the MP2(full)/6-31G(3df,2p) level of theory.
The negative charges present at the endocyclic oxygens in the
oxathiane series (Figure 5) might suggest that the Sδ+---Oδ-
interaction must be more favorable in the 1,3- than in the 1,4-
isomer, with the smaller separation between sulfur and oxygen
in the former structure. The enthalpies of formation, both the
experimental and theoretical values, indicate, however, the
greater stability of the 1,4-isomer. This problem may be
interpreted in light of the theoretical results summarized in
Figure 5. (1) Apparently, electrostatic repulsion Oδ----δ-Oax
S in 1,3-oxathiane sulfone 4 counterbalances, at least in part,
)
Above (see the Introduction), it was supposed that the 1,4-
dithiane sulfone 3 is more stable than the 1,3-isomer 2 due to
the diminished electrostatic repulsion of the two sulfur atoms.
the attractive term. (2) Interestingly, NBO charges may suggest
a stronger Cδ- δ+SO2 bond in 1,4-oxathiane sulfone 5 relative
-
to the 1,3-isomer. Furthermore, less electrostatic repulsion Oδ-
Cδ- is anticipated for the 1,4-oxathiane sulfone, in view of the
-
(20) Juaristi, E.; Cuevas, G. The Anomeric Effect; CRC Press: Boca
Raton, FL, 1995; pp 30-35.
1146 J. Org. Chem., Vol. 72, No. 4, 2007

Study of 1,3- and 1,4-Oxathiane Sulfones
programs.28 The energies of the compound studied were calculated
using Gaussian-2 theory, at the G2(MP2) level,29 and Gaussian-3
theory, at the G3 level.30
essentially neutral carbon atoms adjacent to the endocyclic
oxygen in sulfone 5, in contrast with the negative charge
calculated for the carbon at C(2) in 1,3-oxathiane sulfone 4
(Figure 5).
G2(MP2) and G3 correspond effectively to calculations at the
QCISD(T)/6-311+G(3df,2p) and QCISD(T)/G3large levels, re-
spectively. G3large is a modification of the 6-311+G(3df,2p) basis
set used in G2(MP2) theory and includes more polarization
functions for the second row (3d2f), less on the first row (2df), and
other changes to improve uniformity. In addition, some core
polarization functions are added.30
Experimental Procedures
Material and Purity Control. The procedure described in the
literature21 was slightly modified to synthesize 1,3- and 1,4-
oxathiane sulfone. In a round-bottom 100-mL flask was placed 0.9
mL (9.6 mmol) of 1,4-oxathiane or 1.0 g (9.6 mmol) of 1,3-
oxathiane and 15 mL of acetic acid. The resulting solution was
treated with 15 mL (0.49 mol) of hydrogen peroxide, and the
reaction mixture was stirred at ambient temperature for 2 days. The
solvent was removed at reduced pressure, and the solid residue was
crystallized from CH2Cl2-hexane (2:8). In the case of 1,3-oxathiane
sulfone, final purification was achieved by sublimation (110 °C/4
mmHg) to give the expected sulfone (1.0 g, 77% yield), mp 129-
131 °C (lit. mp 128-130 °C). For 1,4-oxathiane sulfone: (0.9 g,
In both methods, single-point energy calculations are carried out
on MP2(full)/6-31G(d) optimized geometries, incorporating scaled
HF/6-31G(d) zero-point vibrational energies and a so-called higher-
level correction to accommodate remaining deficiencies. G3 also
incorporates a spin-orbit correction for atomic species only.30 We
have also reoptimized the geometries at the MP2(full)/6-31G(3df,2p)
level to obtain more reliable molecular structures for the studied
compounds.
1
69% yield) mp 77-79 °C; H NMR (CDCl3, 300 MHz) δ 2.32-
The charge distribution in the compounds has been analyzed
using a population partition technique, the natural bond orbital
(NBO) analysis of Reed and Weinhold.31,32 The NBO analysis has
been performed using the NBO program33 implemented in the
Gaussian 03 package.28
2.38 (m, 2H), 3.17-3.21 (m, 2H), 3.84-3.88 (t, 2H), 4.53 (s, 2H);
13C NMR (CDCl3, 75 MHz) δ 25.5, 50.9, 68.5, 84.4. Anal. Calcd
for C4H8O3S: C, 35.28; H, 5.92. Found: C, 34.92; H, 6.32.
Both samples were carefully dried under a vacuum at 50 °C.
Determination of purities, assessed by GC and DSC by the fractional
fusion technique,22,23 indicated that the mole fraction of impurities
in all the compounds was less than 0.002. The results obtained in
the characterization and purity control are given in the Supporting
Information.
Fusion enthalpies and heat capacity measurements and the study
of polymorphism of 1,4-oxathiane sulfone were previously carried
out in this laboratory by means of differential scanning
calorimetry.24
Acknowledgment. The support of the Spanish DGI under
Projects QU2003-05827 and FIS2004-02954-C03-01 is grate-
fully acknowledged. M.T. thanks MEC/SEUI, FPU AP2002-
0603, Spain, for financial support. We are also grateful to
Conacyt, Me´xico, for financial support via grant 45157-Q and
to the reviewers for useful comments.
Thermochemical Measurements. The enthalpy of formation in
the gas state, ∆fH°m(g), was determined by combining the standard
enthalpy of formation of the crystalline compounds, ∆fH°m(cr), with
its standard enthalpy of sublimation, ∆subH°m. The enthalpy of
formation in the crystalline state was determined from combustion
calorimetry using an isoperibol combustion calorimeter equipped
with a rotary bomb. Details of the technique and procedure used
have been previously described.25 The energy of combustion was
determined by burning the solid samples in pellet form enclosed
in polyethene bags and using Vaseline as the auxiliary material.
The bomb was filled with oxygen to a pressure of p ) 3.04 Mpa.
From the combustion energy, the enthalpy of formation in the
condensed state was calculated. The enthalpy of sublimation was
determined by measurements of the vapor pressures in the tem-
perature intervals 307-325 and 307-322 K for 1,3- and 1,4-
oxathiane sulfone, respectively, using the Knudsen effusion tech-
nique,26,27 and the enthalpy of sublimation was deduced from the
temperature dependence of the vapor pressures (Clausius-Clap-
eyron). From the experimental results, the standard enthalpies of
combustion, sublimation, and formation in the crystalline and
gaseous states at the temperature of 298.15 K have been derived
and are reported in Table 1.
Supporting Information Available: Experimental details,
comparison of the optimized structures of oxathiane sulfones with
the experimental molecular structures of two derivatives measured
by X-ray diffraction, optimized structures in Cartesian coordinates,
1
and Raman, IR, GC, mass, H NMR, and 13C NMR spectra and
DSC curves used for purity control of 1,3- and 1,4-oxathiane
sulfone. This material is available free of charge via the Internet at
http://pubs.acs.org.
JO0618472
(28) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin, K.
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