Influence of NH⋯N and OH⋯N hydrogen bonds in the aggregation of flexible molecules: A combined experimental and computational study.

Hydrogen bond formation is an important mechanism of molecular aggregation and, therefore, its understanding is crucial to modeling this fundamental process. While extensive literature exists regarding the OH⋯O interaction, NamineH⋯N interactions have been more occasionally studied in gas phase. Here, we study the formation of those two interactions in the context of dimerization of flexible molecules. Using supersonic expansions, we created the conditions to form 2-phenylethylamine homodimers and 2-phenylethylamine⋯2-phenylethanol heterodimers. Structural information was then extracted using mass-resolved excitation spectroscopy. The experimental data were interpreted on the light of computational predictions carried out at the B3LYP-D3(BJ)/def2-TZVP level. Both dimers present a collection of interactions, in addition to the formation of hydrogen bonds. Clearly, the OH⋯N interaction is stronger than the NH⋯N interaction due to the better donor character of the hydroxyl group. However, despite the difference in hydrogen bond strength, both dimers present similar behavior and structure. Comparison with other systems based on similar interactions helps in understanding these results.