Sulfur bond energies

The reason for the conspicuous absence of thermal sources of sulfur atoms lies in the high sulfur bond energies which dictate a temperature for sulfur-atom production usually above the region of thermal stability of the reaction products. 

The standard enthalpy of formation of methanethiol, CH3SH(g), is —22.9 kJ moP. Methanethiol can be synthesized by the reaction of gaseous methanol and H2S(g). Water vapor is another product. Use this information and data from elsewhere in the text to estimate the carbon-to-sulfur bond energy in methanethiol. 

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) ... 

Unlike the stable molecule N2O, the sulfur analogue N2S decomposes above 160 K. In the vapour phase N2S has been detected by high-resolution mass spectrometry. The IR spectrum is dominated by a very strong band at 2040 cm [v(NN)]. The first ionization potential has been determined by photoelectron spectroscopy to be 10.6 eV. " These data indicate that N2S resembles diazomethane, CH2N2, rather than N2O. It decomposes to give N2 and diatomic sulfur, S2, and, hence, elemental sulfur, rather than monoatomic sulfur. Ab initio molecular orbital calculations of bond lengths and bond energies for linear N2S indicate that the resonance structure N =N -S is dominant. 

In general, it was found that this process is strongly endothermic for sulfur diimides, approximately thermoneutral for selenium diimides and strongly exothermic for tellurium diimides, consistent with experimental observations. These differences can be attributed to the expected trend to lower r-bond energies for chalcogen-nitrogen (np-2p) r-bonds along the series S (n = 3), Se (n = 4) and Te (n = 5). 

Sulfur iodides are a topic of considerable current interest, although compounds containing S-I bonds were, in fact, unknown until fairly recently. The failure to prepare sulfur iodides by direct reaction of the elements probably reflects the comparative weakness of the S-I bond an experimental value is not available but extrapolation from representative values for the bond energies of other S-X bonds leads to a value of 170kJmol ... 

Bond Energy Terms in the Chemistry of sulfur. Selenium and Tellurium... 

Considerations of bond energies, which will not be entered into here , similarly do not give a clear answer to this structural problem. Studies of the infrared spectra of sulfoxides and sulfones enable force constants of the sulfur-oxygen bonds to be calculated with various groups attached to sulfur. Again, these have been variously interpreted and no clear indication as to the nature of the sulfur-oxygen bond emerges. ... 

The 0=0 and S=S bond energies are 498 and 431 kj mol-1, respectively, and the 0-0 and S-S bond energies are 142 and 264. Explain why it is reasonable to expect structures containing sulfur that have extensive catenation but such structures are not expected for oxygen. 

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