Low temperature studies on ultraviolet and infrared spectra of ortho Mannich bases

Low temperature studies of UV and IR spectra have been performed for 2-(N,N -dimethylaminomethyl)-4,6-dichlorophenol (Cl2MB), 2-(N,N-diethylaminomethyl )-3,4,6-trichlorophenol (CI,MB) and 2-(N,N-diethylaminomethyl)-tetrachlorop henol (Cl4MB) in n-butylchloride, which undergoes transition to the glassy state at 150 K. The proton transfer (PT) equilibrium in the liquid state is clearly seen only for Cl4MB. In the case of Cl3MB, negligible amounts of t he PT species are observed in liquid phase above 150 K, and complete PT tak es place below the glassy state transition. No PT was detected for Cl2MB do wn to 90 K. The temperature effects on the high frequency region and backgr ound IR absorption extended down to 650 cm(-1) are analyzed. The broad abso rption below 1600 cm(-1) vanishes for Cl4MB and Cl3MB on cooling when they transform to the PT ion pairs. The potential energy curve for ion-pairs is characterized by a single minimum. (C) 1999 Elsevier Science B.V, All right s reserved.