A Raman study on preferential interactions in the formamide/pyridine/pyridazine system and complementary thermodynamic information on the formamide/pyridazine mixture

The formamide (FA)/pyridine (py)/pyridazine (prd) system was investigated by FT-Raman spectroscopy and the results in situ show that FA is preferentially bound to py, as experimentally pointed out by the proton affinity (PA) values of these azabenzenes. Temperature-dependent further investigations for the FA/prd mixture clearly show that the 2:1 FA:prd complex is more stable than the 1:1 FA:py adduct, even though its formation is influenced by the extremely negative entropy of the system, which becomes the spontaneously unfavorable global process. Linear relationships of the complex formation enthalpies (ΔH°) with band shifts (Δν) and dipole moments (μ) of these azabenzenes are observed and are in excellent agreement with our recent studies.

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► An FT-Raman spectroscopic study of ternary and binary mixtures is presented.
► The basic strength of pyridine and pyridazine towards FA is evaluated in situ.
► Pyridine is the strongest base.
► The complex with pyridazine is the most stable.
► The negative entropy plays an important role.