Calorimetric and computational study of 1,4-dithiacyclohexane 1,1-dioxide (1,4-dithiane sulfone)

This work reports the enthalpies of formation in the condensed and gas state of 1,4-dithiacyclohexane 1,1-dioxide (1,4-dithiane sulfone, 5), derived from the enthalpy of combustion in oxygen, measured by a rotating bomb calorimeter and the variation of vapor pressures with temperatures determined by the Knudsen effusion technique. The theoretically estimated enthalpy of formation was calculated from high-level ab initio molecular orbital calculations at the G2(MP2) level. The theoretical calculations appear to be in very good agreement with experiment. A comparison of the conversion of thiane sulfone 3 to 1,3-dithiane sulfone 4 and 1,4-dithiane sulfone 5 clearly shows the 1,3 isomer to be 6.7 kJ mol(-1) less stable, probably owing to diminished electrostatic repulsion between the sulfur heteroatoms in 1,4-sulfone 5.     

Calorimetric and computational study of 1,3-dithiacyclohexane 1,1-dioxide (1,3-dithiane sulfone)

The enthalpies of combustion and sublimation of 1,3-dithiacyclohexane 1,1-dioxide (1,3-dithiane sulfone) were measured by a rotating-bomb combustion calorimeter and the Knudsen effusion technique, and the gas-phase enthalpy of formation was determined, Delta(f)H(m)*(g) = -326.3 +/- 2.0 kJ mol(-1). Standard ab initio molecular orbital calculations at the G2(MP2) level were performed, and a theoretical study on molecular and electronic structure of the compound has been carried out. Calculated Delta(f)H(m)*(g) values agree very well with the experimental one. These experimental and theoretical studies support the relevance of the repulsive electrostatic interaction between sulfur atoms in 1,3-dithiane sulfone, that apparently counterbalances any n(S) --> rho(C-SO2)* stabilizing hyperconjugative interaction.     

13C and 17O chemical shifts and conformational analysis of mono- and di-methyl-substituted thiane 1-oxide and thiane 1,1-dioxide

The ¹³C and ¹⁷O (natural abundance) chemical shifts of several mono- and di-methyl ring-substituted thiane 1-oxides and thiane 1,1-dioxides are reported. The cis and trans isomers of methyl-substituted thiane 1-oxide are readily identified by ¹³C and ¹⁷O NMR. In particular, the ¹⁷O NMR signals of axial SO groups are found several ppm upfield of those of the equatorial counterparts. The proportion of axial and equatorial conformers of thiane 1-oxide in different solvents has been measured by low-temperature ¹³C NMR. In THF the proportion of the axial conformer is higher than in CD₂Cl₂ whereas in CDCl₃ or CHF₂Cl the conformational preference is reversed and the equatorial conformer is slightly favoured.     

Deformation C-S and S=O bond polarizations in dimethyl sulfoxide

The data on the permittivities of crystalline 1,4-dithiane and 1,4-dithiane-1,4-dioxide were used to calculate the molar deformation polarizations of the C-S (P _{∞, C-S} = 3.84 cm³/mol) and S$ \underline \ldots $ \underline \ldots O ($ P_{\infty ,S\underline \ldots O} $ P_{\infty ,S\underline \ldots O} = 4.34 cm³/mol) bonds within the framework of the additive scheme suggested by Levin. These data were used to calculate the deformation permittivity of dimethylsulfoxide (DMSO) at 298.15 K, ɛ_{∞, DMSO} = 2.36, and the dipole correlation factor of pure DMSO, g ^dip = 1.055.     

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.     

DFT study of molecular structures and relative stabilities of 1,2,7-thiadiazepane 1,1-dioxide and 1,2,7-thiadiazepane 1-oxide

The structures and energies of 1,2,7-thiadiazepane 1,1-dioxide and the axial and equatorial conformers of 1,2,7-thiadiazepane 1-oxide were calculated using the hybrid density functional B3LYP with the cc-pVDZ basis set. The results obtained explain the lower stabilities of equatorial conformers compared to the axial analogs and the lower stabilities of sulfones compared to sulfoxides.

     

AM1 computational study of cycloaddition reaction of vinyl sulfene generated from thiete 1,1-dioxide

Theoretical studies of the cycloaddition reaction between vinyl sulfene, norbornene and related systems are presented. Since the parameterized AMI semiempirical method was used, the generated data are only of qualitative value. The vinyl sulfene reactivity was assessed by using frontier molecular orbital (FMO) energy gaps, bond orders, and the charge distribution of the reactants. To obtain more information, as far as the reaction outcome and its feasibility, the transition state structures and activation barriers for competitive pathways are computed.     

Synthesis of 4H-1,4-benzothiazine 1-oxide and 1,1-dioxide. Analogs of quinolone antibacterial agents

4-Cyclopropyl-5,7-difluoro-6-(4-methyl-1-piperazinyl)-4H-1,4-benzothiazine-2-carboxylic acid 1-oxide (2c) and 4-cyclopropyl-5,7-difluoro-6-(4-methyl-1-piperazinyl)-4H-1,4-benzothiazine-2-carboxylic acid 1,1-dioxide (2d) were prepared and assayed for antibacterial activity and inhibition of DNA gyrase.     

Comparison of the reactivity of thiophene,thiophene 1-oxide,and thiophene 1,1-dioxide as diene for diels-alder reactions. An ami semiempirical study

A semiempirical AMI theoretical study was carried out to examine the very low reactivity of thiophene; for example, the high reactivity of thiophene 1-oxide as a diene in the Diels Alder reactions. The reactivities of cyclopentadiene, thiophene, thiophene 1-oxide, and thiophene 1,1-dioxide were studied as dienes in the reaction with ethylene, cyclopropene, and benzoquinone. Ethylene was chosen as a standard, while cyclopropene, with its high strain energy was released in the course of a reaction making it relatively reactive. The benzoquinone has a lower LUMO energy, making it a very reactive dienophile for the Diels-Alder reaction. Frontier molecular orbital energy gap between the reactants was considered, and the disadvantage of this approach in studying the reactivity was demonstrated. For all combinations, the corresponding transition structures are generated and the activation energies are estimated. The estimated activation barrier for sulfur dioxide elimination from the adduct was used to explain the failure to accumulate the cycloadduct in the reaction mixture. The obtained results are compared with experimental data when available. An excellent agreement of theory and experiment was obtained.     

Crystal structures and theoretical calculations of trans-2,4,4-trimethyl-4-silathiane 1-oxide and 4,4-dimethyl-4-silathiane 1,1-dioxide

The crystal and molecular structures of trans-2,4,4-trimethyl-4-silathiane 1-oxide 1 and 4,4-dimethyl-4-silathiane 1,1-dioxide 2 were determined by single crystal X-ray diffraction. Both compounds have the chair conformation with the 2-Me and the S=O group in compound 1 occupying the equatorial positions. The DFT (B3LYP/6-311G(d,p)) and MP2 (MP2/6-311G(d,p)) theoretical calculations nicely reproduce the X-ray experimental geometry. The obtained results are discussed in connection with the electronic and structural properties of the compounds.

Calorimetric and computational study of the thermochemistry of phenoxyphenols

Thermodynamic properties of 3- and 4-phenoxyphenol have been determined by using a combination of calorimetric and effusion techniques as well as by high-level ab initio molecular orbital calculations. The standard (p° = 0.1 MPa) molar enthalpies of formation in the condensed and gas states, Δ(f)H(m)°(cr or l) and Δ(f)H(m)°(g), at T = 298.15 K, of 3- and 4-phenoxyphenol were derived from their energies of combustion in oxygen, measured by a static bomb calorimeter, and from the enthalpies of vaporization or sublimation derived respectively by Calvet microcalorimetry for the 3-phenoxyphenol and by Knudsen effusion technique for the 4-phenoxyphenol. The theoretically estimated gas-phase enthalpies of formation were calculated from high-level ab initio molecular orbital calculations at the G3(MP2)//B3LYP level of theory. Furthermore, this composite approach was also used to obtain information about the gas-phase acidities, gas-phase basicities, proton and electron affinities, adiabatic ionization enthalpies, and, finally, O?H bond dissociation enthalpies. The good agreement between the G3MP2B3-derived values and the experimental gas-phase enthalpies of formation for the 3- and 4-phenoxyphenol gives confidence to the estimate concerning the 2-phenoxyphenol isomer, which was not experimentally studied, and to the estimates concerning the radical and the anion. Additionally, the experimental values of gas-phase enthalpies of formation were also compared with estimates based on the empirical scheme developed by Cox.     

Potential energy surface of the system CO + O: An ab initio study on the O?CO bond formation

Quantum mechanical computations on the potential energy surface of the system CO + O at an SCF –MO ab initio level are presented and discussed. The calculations are performed on a minimal basis set of atomic functions. Comparison with results obtained with extended basis sets are also presented.     

Calorimetric and computational study of 3-buten-1-ol and 3-butyn-1-ol. Estimation of the enthalpies of formation of 1-alkenols and 1-alkynols

The enthalpies of combustion and vaporization of 3-buten-1-ol and 3-butyn-1-ol have been measured by static bomb combustion calorimetry and correlation gas chromatography techniques, respectively, and the gas-phase enthalpies of formation, Delta(f)H degrees (m)(g), have been determined, the values being -147.3 +/- 1.8 and 16.7 +/- 1.6 kJ mol(-1), for 3-buten-1-ol and 3-butyn-1-ol, respectively. High level calculations at the G2 and G3 levels have also been carried out. Relationships between the enthalpies of formation of 1-alkanols, 1-alkenols and 1-alkynols and with the corresponding hydrocarbons have been discussed. From the calculated contributions to Delta(f)H degrees (m)(g) for the substitutions of CH(3) by CH(2)OH, CH(3)CH(2) by CH(2)=CH and CH(3)CH(2) by CH triple bond C, we have estimated the Delta(f)H degrees (m)(g) values for 3-buten-1-ol and 3-butyn-1-ol, in excellent agreement with the experimental ones. Delta(f)H degrees (m)(g) values for 1-alkenols and 1-alkynols up to 10 carbon atoms have also been estimated.     

A computational study of O-O bond formation catalyzed by mono- and bis-MnIV-corrole complexes

A detailed computational study of O-O bond formation, catalyzed by monomeric and dimeric Mn-corrole complexes, is reported. The model explicitly takes into account the solvent, with respect to the first and second coordination spheres, while the bulk solvent is described by the polarizable continuum model. Two reaction mechanisms are proposed and computationally characterized: the concerted and the two-step mechanisms. The concerted mechanism is based on a OH--MnIVO interaction via the outer-sphere pathway involving the bridging solvent molecules in the first coordinating sphere. The two-step mechanism is proposed to operate via the coordination of a hydroxide to the MnIV ion, forming a MnO(OH)--corrole complex with a strongly nonplanar corrole ligand. Comparison of the proposed mechanisms with available experimental data is performed.     

Conformation energy around the N(sp3)?O single bond

A detailed conformational analysis was performed on simple substituted hydroxylamines using either ab initio (from HF/6-31G* to RQCISD/6-311G**) or popular semiempirical (MNDO, AM1, PM3) methods to ascertain the allowed conformations and to establish the influence of the level of theory on the results. All the ab initio results (provision being made for their expected divergences) are similar and show a simple twofold character for the > N? O? rotational energy, without any appreciable populations of the cis conformer. On the other hand, the predictive value of the semiempirical methods for structural and energetical parameters of molecules bearing > N? O? moieties is limited, a situation like that prevailing for peptide bonds. The inversional barriers for the methyl-substituted hydroxylamines were also calculated and compared to the corresponding rotational energy barriers. Rotation is generally favored over inversion for hydroxylamine and its methylated derivatives. © 1994 by John Wiley & Sons, Inc.     

Selective synthesis of di(propen-1-yl)sulfone and di(propen-1-yl)sulfoxide

Convenient selective methods of synthesis of the title compounds, based on oxidation of di(propen-1-yl)sulfide with 30% H₂O₂, have been developed.Institute of Organic Chemistry, Siberian Branch, Russian Academy of Sciences, 664033 Irkutsk. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 3, pp. 675–679, March, 1992.