Abstract
The OH proton chemical shifts are reported of dilution study of 2-methyl-6- t-butylphenol (2M6TBP) and 2,6-di- t-butylphenol (2.6DTBP), and of the 1:1 association between the phenols and hexamethylphosphoramide (HMPA) in C 6H 12, CCl 4, CH 3NO 2, CH 3CN and C 6H 6 at 25, 35 and 50°C. Also the association of the phenols with CH 3NO 2, CH 3CN and CCl 4 has been studied. The phenol OH chemical shift, δ f , found by extrapolation to zero concentration, shows the highest upfield shift in benzene. Contrary, on adding HMPA, the complex OH chemical shift, δ x , shows the lowest downfield shift in benzene. The K ass, δ x , ΔH and ΔS values have been evaluated by using the Hiquchi plot method. Linear relationships were obtained between Δδ x and ΔH, and log K ass for the system 2M6TBP/HMPA in the various solvents. Furthermore, the difference in H-bond energy of a given system in an inert solvent (C 6H 12) and in aprotic solvent (CH 3CN), corresponds to the enthalpy of association of the given donor with CH 3CN in C 6H 12. The K ass value for the system 2M6TBP/HMPA is 10 times greater in C 6H 12 than in C 6H 6 and CCl 4, 100 times than in CH 3NO 2 and 300 times than in CH 3CN.
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