Sulfur lone pair

Although isothiazole (pK = 1.90) is less basic than thiazole, its rale of quaternization by dinitrophenyl acetate in water at 52°C is approximately 2.5 times higher (447). This deviation from the Bronsted relationship (A log k - 0.ApK, with positive) is interpreted as a consequence of the or effect of the adjacent sulfur lone pair in isothiazole that is responsible for its higher nucleophilicity (448, 449). 

FIGURE 1. Sulfur lone-pair and %<, ionization patterns in 1,3-dithietane, thietane oxide and 1,3-dithietane oxide. 

The behavior of v(C=C) also indicates strong conjugation in methyl vinyl sulfide through the participation of one of the sulfur lone pairs in 7i(pp) bonding (cf. 15). v(C=C)... 

C20-0102. Blue copper proteins are blue when they contain Cu but colorless as Cu compounds. The color comes from an interaction in which a photon causes an electron to transfer from a sulfur lone pair on a cysteine iigand to the copper center. Why does this charge transfer interaction occur for Cu but not Cu+ ... 

There is little information for fluoro-substituted sulfinyl groups. Values of a and ffp for SOCFj based on benzoic acid ionization are 0.63 and 0.69 respectively , compared with values of about 0.52 and 0.49 for SOMe (Table 3). Thus the electronegative fluorine somewhat enhances the electron-attracting influence of the sulfinyl function and makes the order more definitely [Pg.509]

The (Tj value for SOMe is slightly different from that given by Taft and Lewis . The continuous increase in a, produced by attached electronegative atoms at S or C is, of course, to be expected. This also encourages octet expansion as measured by The zero value for SOMe presumably means that any tendency to octet expansion [conventionally n (pd) conjugation] is essentially cancelled by the n (pp) conjugation of the sulfur lone pair. For these -f R substituents no exaltation of (Tj,-type values in the direction - (Tj would be expected. The table shows two (T -type constants phenol dissociation. We have already... 

Species 4, produced from thianthrene by loss of an electron from a sulfur, is correctly known as thianthrene radical ion(l+) most authors have referred to it as the thianthrene radical cation or the thianthrene cation radical. The species produced by loss of two electrons from the central ring, and for which 5 is probably a resonance contributor, is termed thianthrenediium. Sulfonium salts (6) produced formally by utilizing a sulfur lone-pair in bonding to, are 5-R-thianthrenium salts. Thianthrene... 

The folded nature thus demonstrated experimentally is consistent with the conclusion (63T471 64JA164) from molecular orbital (MO) calculations that, in thianthrene, there is little overlap between a sulfur lone pair and the two p orbitals adjacent to it (78PS1). Similarly, later calculations showed that the resonance energy of thianthrene is essentially that of the two benzene rings (80T2711). 

Effects of Nitrogen and Sulfur Lone Pairs on H, 13C and N Chemical Shifts... 

From the slopes of the plots, substituent constants cra+ (-0.79) and cr0+ (-0.52) have been calculated these relate to the perturbations caused by the substitution of a sulfur atom for a —CH=CH— group in the benzene ring. The linearity observed in the plot of log af against p implies the absence of steric effects due to the sulfur lone pairs on the reactivity at the a-position. 

Non-planarity is the result of the dominance of the destabilizing interactions of the sulfur lone pair and tt- occupied MOs of the pentadienyl anion over the stabilizing interaction of that lone pair and the LUMO of the anion fragment. In fact thiabenzene is antiaromatic in a planar configuration. Pyramidalization reduces the antiaromaticity induced by the sulfur. Although no X-ray data are available on the parent system, kinetic data have been obtained supporting a minimum barrier to inversion at the pyramidal sulfur of a 2-thianaphthalene of 99.1 kJ mol-1 (75JA2718). The formulation of the system as a cyclic ylide is supported by the chemical reactivity of the compounds as related in the reactivity section below. 

Even one phosphine ligand in [Co(PR3)2( 175-CSHS)] (PR3 = PMe3, PMe2Ph) could be replaced by S = CPh2 to afford [Co(PR3)(V-S = CPh2)(775-C5H5)] complexes in which the thioketone ligand is bound via a sulfur lone pair.139... 

A mostly qualitative MO approach was used by Alvarez, Vicente and Hoffmann140 to interpret the regularities and irregularities in the dimerization and stacking of transition metal dithiolenes. While firm predictions could not be made, the balance between sulfur lone-pair repulsion, size and occupation of the metal d-orbitals and substitutent steric demand were pointed out. The coordination preference of ethylenetetrathiolate was determined to be of the 1,2-dithiolene type rather than the 1,1-dithiolene. This result was suggested to apply both to binuclear and polymeric species. 

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