The interaction between all-trans retinylidene isopropylamine (tRiPA) and phenols covering a large pKa domain is investigated by FT-infrared spectrometry. For phenols having pKa between 10.2 and 8.18, only normal OH … N hydrogen bonds are formed. The thermodynamic parameters (K, −ΔH, −ΔS0) determined in carbon tetrachloride solution show that tRiPA possesses a good proton acceptor ability. The spectral characteristics (frequency and integrated intensity) of the νC=N vibration are also investigated. From a pKa of 6, proton transfer takes place. The proton transfer constants determined in 1,2-dichloroethane are linearly related to ΔpKa (pKa of the protonated base minus pKa of the phenol). Comparison with previously studied imine systems shows that the proton transfer constant increases with the number of C=C double bonds in the base.
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