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A NMR study of trimethylacetic acid self‐association
Author(s) -
Kimtys L.
Publication year - 1975
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.1270070409
Subject(s) - cyclohexane , chemical shift , enthalpy , chemistry , melting point , equilibrium constant , entropy (arrow of time) , analytical chemistry (journal) , thermodynamics , organic chemistry , physics
The carboxyl proton chemical shifts of neat trimethylacetic acid and its solutions in cyclohexane have been measured as a function of temperature. Formation, at the melting point, of a carboxyl group satellite line on the low field side has been found. The intensity of this satellite line rises with decreasing temperature, whereas the intensity of the main line decreases. The chemical shifts of the monomer (δ m = 4·9 ± 0·6 ppm) and dimers, the equilibrium constants, enthalpy (Δ H = −(11·3 ± 0·6) kcal/mol) and entropy (Δ S = −(13·5 ± 0·7) cal/mol. degree) changes have been calculated using the concentration dependence of the chemical shifts of trimethylacetic acid in cyclohexane solutions at various temperatures. The chemical shift of the satellite line has been shown to correspond to the chemical shift of the cyclic dimers of the acid.