Effect of methyl group on the cooperativity between cation-π interaction and NH···O hydrogen bonding

B3LYP/6-31++G(d,p) and MP2/6-31++G(d,p) methods have been used to study the ternary systems constituted with Na+, pyrrole/methylated pyrrole and water/dimethylether, and the corresponding binary systems. The structures, energetics and spectroscopic properties of these systems have been investigated to evaluate the role of methyl group in the cation-π interaction, NH···O hydrogen bond and the cooperativity between two interactions. The methylated pyrrole is favorable for the cation-π interaction, whereas it is unfavorable for the NH···O hydrogen bond. In the formation of NH···O hydrogen bond, the methyl group in the proton donor is electron-withdrawing and that in the proton acceptor is electron-donating. The former plays a negative contribution and the latter plays a positive contribution to the formation of NH···O hydrogen bond. The methyl group in methylated pyrrole decreases the cooperativity between the two interactions, whereas that in dimethylether increases the cooperativity. Many-body interaction analyzes have also been performed for the ternary systems.