Selective induced polarization through electron transfer in acetone and pyrazole ester derivatives via C–H⋯OC interaction

Abstract

A set of organic compounds (pyrazole ester derivatives, viz. 5-[3-(substituted)-propoxy]-3-methyl-1-phenyl-1H-pyrazole-4-carboxylic acid methyl ester and 5-[2-(substituted)-ethoxy]-3-methyl-1-phenyl-1H-pyrazole-4-carboxylic acid methyl ester) was synthesized and their affinity and stability towards the acetone molecule were tested by NMR. Further, the host–guest complex formed has been studied by cyclic voltammetric titration. Interestingly, the acetone molecule selectively bound to the methyl group of the pyrazole moiety and stabilized the system. These findings are also supported by quantum chemical calculations using the DFT/B-LYP/TZVPP method. Apart from hydrogen bonding, an important role in stabilizing the complex is also played by the C–H⋯π interaction governed by dispersion energy. The study proves that a methyl-substituted pyrazol ester can act as a receptor for acetone.