Theoretical investigation of the nature of hydrogen bonds and cooperativity effect in methanol-water and ethanol-water clusters.

This study aims to cast light on the nature of hydrogen bonds and their cooperativity that exists in alcohol-water ( $ \textrm{ROH}{({{\textrm{H}_2}\textrm{O}})_\textrm{n}} $ ROH ( H 2 O ) n ) ( $ \textrm{R} = - \textrm{C}{\textrm{H}_3}\textrm{ }({ - \textrm{Me}}),\textrm{ } - \textrm{C}{\textrm{H}_2}\textrm{C}{\textrm{H}_3}\textrm{ }({ - \textrm{Et}}) $ R = − C H 3 (− Me) , − C H 2 C H 3 (− Et)) (n = 1–10) clusters using atoms in molecules (AIM) theory and symmetry-adapted perturbation theory (SAPT). The investigation of optimum structures suggests that alcohol ( $ \textrm{ROH} $ ROH ) forms two hydrogen bonds, one primary hydrogen bond $ ({\textrm{O} - \textrm{H} \cdot \cdot \cdot \textrm{O}}) $ (O − H ⋅ ⋅ ⋅ O) , and one secondary hydrogen bond $ ({\textrm{C} - \textrm{H} \cdot \cdot \cdot \textrm{O}}) $ (C − H ⋅ ⋅ ⋅ O) Two types of hydrogen bonds are addressed in these studies, where alcohol works as the hydrogen bond donor $ ({\textrm{ROH} \cdot \cdot \cdot \textrm{O}{\textrm{H}_2}}) $ (ROH ⋅ ⋅ ⋅ O H 2 ) and hydrogen bond acceptor $ ({\textrm{RHO} \cdot \cdot \cdot \textrm{HOH}}) $ (RHO ⋅ ⋅ ⋅ HOH). The AIM results reveal that $ \textrm{RHO} \cdot \cdot \cdot \textrm{HOH} $ RHO ⋅ ⋅ ⋅ HOH and $ \textrm{ROH} \cdot \cdot \cdot \textrm{O}{\textrm{H}_2} $ ROH ⋅ ⋅ ⋅ O H 2 hydrogen bonds are partially covalent. The SAPT study demonstrates that in all the clusters studied herein, the electrostatic interaction between alcohol and water is the main attractive force, and its contribution may be two times larger than the separate corresponding contributions from the dispersion and the induction terms. The electron density (ρ) at the bond critical point (BCP) is a suitable parameter to assess the strength of the interaction. The current study shows the strength and nature of $ \textrm{ROH} \cdot \cdot \cdot \textrm{O}{\textrm{H}_2} $ ROH ⋅ ⋅ ⋅ O H 2 and $ \textrm{RHO} \cdot \cdot \cdot \textrm{HOH} $ RHO ⋅ ⋅ ⋅ HOH hydrogen bond, and cooperative effect in ( $ \textrm{ROH}{({{\textrm{H}_2}\textrm{O}})_\textrm{n}} $ ROH ( H 2 O ) n ) ( $ \textrm{R} = - \textrm{C}{\textrm{H}_3}\textrm{ }({ - \textrm{Me}}),\textrm{ } - \textrm{C}{\textrm{H}_2}\textrm{C}{\textrm{H}_3}\textrm{ }({ - \textrm{Et}}) $ R = − C H 3 (− Me) , − C H 2 C H 3 (− Et).) (n = 1–10). [ABSTRACT FROM AUTHOR]