Thiols protonation

Embedded within this list of DPE of the amino acids are two unexpected results concerning what is the most acidic proton. The first case is cysteine, where one might ask which is more acidic, the carboxylate proton or the thiol proton Kass and Poutsma" note that, in general, the gas-phase acidity of carboxylic acids is greater than thiols the DPE of propanoic acid (CH3CH2CO2H) is 347.7 kcal mol at G3B3 (347.2 expt about 6 kcal mol less than that of ethanethiol (CH2CH2SH ... 

Sulfur-containing SBs such as thiosemicarbazones or selenosemicarbazones may also exhibit in solution a tautomerism between the thione (7a) and the thiol forms (7b) as indicated in Scheme 4. The tautomer (7a) acts as a neutral bidentate ligand, while the loss of the thiol proton of tautomer (7b) yields a single-charged bidentate ligand.29... 

Spectroscopic and Related Properties of Thiols.— The n.m.r. absorption of the thiol proton moves to lower field in the order PhCHa SH, PhjCH SH, PhaC SH corresponding hydrotrisulphides RSS SH show the opposite sequence, due to over-riding inductive and anisotropic effects within the cumulative sulphur chain. 

For the adsorption of cadmium ions by the solid extractant SOL-AD-IV synthesized by the technique described in Section 12.2.3, the reaction can be assumed to be a cationic exchange with the thiol proton. The general reversible reaction can be... 

The carbon of the aldehyde carbonyl is attacked by the thiolate anion. The thiol proton Is picked up by a basic site. 

The coupling of the partial electron transfer and proton dissociation via the electro-neutrality requirement holds only for the case of the LB experiments described here. Thus, the extent of proton dissociation following alkanethiol self-assembly is not subject to this limitation and may proceed to a larger extent. Indeed, vibrational spectroscopic data reporting absence of the thiol proton would suggest its complete dissociation. 

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