Electronegativity, of the sulphur atom

Edwards two-parameter equation 549 Electrochemical oxidation of sulphides 76, 252, 253 of sulphoxides 968, 987, 1043 Electrochemical reduction of sulphones 962, 963, 1002-1041 of sulphoxides 933, 1041, 1042 Electronegativity, of the sulphur atom 584 Electronic effects 390, 484-535 Electron scavengers 892, 896 Electron spin resonance spectroscopy 874, 890-895, 1050-1055, 1082, 1083, 1090-1093... 

The sum of the covalent radii3 for silicon and sulphur is 2.21 A. The electronegativity of the sulphur atom is smaller than that of its congener oxygen atom and therefore the expected polarization and ionicity of the Si—S bond is smaller than that of the Si—O bond. As a result it is expected that the shortening of the Si—S bond length from the sum of covalent radii will be significantly smaller than that observed for the Si—O bond. 

The C=0 effective bond charges determined are higher than the respective C=S values in the sulphur analogs. This fmding is also in accord with the lower polarity of the C=S bonds due to lower electronegativity of the sulphur atom. 

In many cases, experimental data have been discussed in terms of variations of the paramagnetic contribution, nuclear shielding constant (Equation (2)). Empirical correlations with parameters related to the electronic properties of other substituents in the molecule (electronegativities, Hammett substituent constants etc.) have been found. This kind of investigation has provided useful information about the electronic structure of the sulphur atom in different bonding situations and most of all about the electronic properties of the S-O bond, which is still a rather controversial matter. 

The substituted boron halides, BX3 (SeH) (X = C1, Br, or I) are considered to be planar on the basis of vibrational spectroscopic data. These data are readily comparable with those of the sulphur analogues, but from force-field calculations it was shown that the B—Se bond is particularly sensitive to the electronegativity of the attached halogen atoms. The shape of the y(SeH) band in BC SeH has been investigated in detail to show a tunnel effect for the hydrogen atom. 

Thiol esters have been studied by Rasmussen [18], and more recently by Nyquist and Potts [82] and Baker and Harris [83]. Dialkyl thiolesters show their carbonyl bands in the narrow range 1698 to 1690cm". The reasons for this substantial fall as compared with normal esters are not fully understood and have been the subject of some controversy [80]. However, it is probably a direct consequence of the low electronegativity of sulphur. a -Con-jugation in aryl alkyl thiolesters lowers the frequency to 1665 to 1670 cm" which is a rather larger shift than is found in esters. On the other hand the rise in frequency when an aromatic ring is attached to the sulphur atom is less than in the phenyl esters, and such compounds absorb near 1710 cm". ... 

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