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Self‐association of thiols. The baggy fit problem in weak complexes
Author(s) -
Hu Siung J.,
Miller Sidney I.
Publication year - 1973
Publication title -
organic magnetic resonance
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0030-4921
DOI - 10.1002/mrc.1270050407
Subject(s) - trustworthiness , chemistry , hydrogen bond , dilution , anisotropy , association (psychology) , crystallography , molecule , physics , thermodynamics , computer science , quantum mechanics , organic chemistry , psychology , computer security , psychotherapist
The PMR technique has been used to obtain thermodynamic data for hydrogen bonding of alkanethiols (RSH) in 1:1 dimers in carbon tetrachloride. At ca . 303°K these are (R, 10 4 K ( M −1 ), −Δ H °(kcal/mole), −Δ S °(eu)): n ‐C 3 H 7 , 51 ± 5, 0.9 ± 0.15, 13 ± 1; i ‐C 3 H 7 , 50 ± 10, 0.8 ± 0.3, 13 ± 1; n ‐C 4 H 9 , 35 ± 2, 0.8 ± 0.15, 14 ± 1; t ‐C 4 H 9 , 14 ± 4, 1.1 ± 0.7, 16 ± 2; C 6 H 11 , 1.3 ± 2, 0.7 ± 0.3, 15 ± 1. Alkanethiol self‐association is weak, and although an exact expression [Eqn. (5)] reproduces spectral data precisely, the fit is sufficiently ‘loose’ or ‘baggy’ so that values of K , Δ H ° and Δ S ° are uncertain. The methodology of the treatment of self‐association data and their errors is examined and Deranleau's useful approach is extended. The impossibility of obtaining reliable data for very weak (< 10 %) or very strong (> 90 %) associations by techniques equivalent to ours is emphasized. The possibility of cyclic thiol dimers is discussed. It is suggested that the PMR method cannot give trustworthy self‐association data for aryl or arylalkylthiols because of the relatively large anisotropy effects introduced into the dilution shift.