Bond dissociation energy sulfur

Thermal Properties. Thermodynamic stabiUty of the chemical bonds comprising the PPS backbone is quite high. The bond dissociation energies (at 25°C) for the carbon—carbon, carbon—hydrogen, and carbon—sulfur bonds found in PPS are as follows C—C, 477 kj/mol (114 kcal/mol) ... 

However, the fact that the derived S—O bond dissociation energy in sulfuric acid is identical to that found in the acid derivatives, strongly supports the estimated enthalpy of formation for gas-phase sulfurous acid given by Benson18. 

The bond dissociation energies in the gas phase for Me—SO2, Et—SO2 and Ph— SO2 have been evaluated to be 18, 16 and 44kcalmol respectively although Horowitz, from complex kinetic studies of the radiolysis of MeS02Cl in cyclohexane, has obtained the values of 15 and 12 kcal mol for D(Me—SOy and D(c-C6Hn—SO2), respectively these bond dissociation energies are considerably lower than the gas-phase values, and it has been suggested that the possible cause of this difference is due to the heat of vaporization of sulfur dioxide . 

Table 2. Bond dissociation energies of alkenes, alkynes, and aromatics Table 3. Bond dissociation energies of C/H/O compounds Table 4. Bond dissociation energies of sulfur-containing compounds Table 5. Bond dissociation energies of nitrogen-containing compounds Table 6. Bond dissociation of halocarbons...

TABLE D4 Bond Dissociation Energies of Sulfur-Containing Compounds... 

The S-H absorption is typically weak and occurs at a lower wavenumber (frequency) than the corresponding 0-H vibration because of the higher atomic mass of sulfur (and so increased reduced mass of SH). The difference in reduced mass, however, does not completely account for the reduction in the stretching frequency of the S-H bond as this bond is also generally weaker (smaller k) than the corresponding O-H bond (typical bond dissociation energies OH, 460 kJ mol SH, 340 kJ mol ). 

Advantage has been taken of the ready accessibility of eleven para-substituted trityl and 9-phenylxanthyl cations, radicals, and carbanions in a study of the quantitative relationship between their stabilities under similar conditions.2 Hammett-type correlations have also been demonstrated for each series. Heats and free energies of deprotonation and the first and second oxidation potentials of the resulting carbanions were compared. The first and second reduction potentials and the p/CR values of the cations in aqueous sulfuric acid were compared, as were calorimetric heats of hydride transfer from cyanoborohydride ion. For radicals, consistent results were obtained for bond dissociation energies derived, alternatively, from the carbocation and its reduction potential or from the carbanion and its oxidation potential. 

Data on the physical and chemical properties of PCDTs and PCTAs are scarce. Due to their structural similarity to PCDFs and PCDDs they are also supposed to possess some likeness in their physical and chemical properties. Sulfur and oxygen are both Group VI elements with two outer shell electrons available for covalent bonding. Structures of thiophene and furan with benzene carbon-sulfur (Cb-S) and carbon-oxygen bond (Cb-0), in PCDTs and PCDFs respectively, suggest similar chemical behavior. The bond dissociation energies (AH) show that less energy is required to break the Cb-S bond than the Cb-0 bond [17,36,37]. 

In general, the thermal stability of polysulfides decreases as the length of the polysulfide linkage increases. The bond dissociation energies of dimethyl di-, tri-and tetrasulfides follow the same trend, being 69, 46 and 37 kcaLmole", respectively this has been rationalized in terms of resonance interaction of the free electron with the sulfur chain... 

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