The temperature dependence of1H NMR chemical shift of -COOH group for the ternary system A+B+S (A - R-COOH component, B - electrondonating, S - inert solvent) ussually has a continuous character. However the experimentally measured dependences δ(COOH) = f(T) for the trimethylacetic acid (TA)-acetone-n-hexane system have uneven changes of the chemical shift at a certain temperature in the region 233–190 K (Ref. 1). It may be caused by the phase separation of solvents B + S, since it is well-known phenomenon for the mixtures acetonehydrocarbon2.