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The role of chirality in the competition between inter and intramolecular hydrogen bonds: jet-cooled van der Waals complexes of (±)2-naphthyl-1-ethanol with (±)1-amino-2-propanol and (±)2-amino-1-butanol

The structure of jet-cooled complexes of (±) 2-naphtyl-1-ethanol with (±) 1-amino-2-propanol and (±) 2-amino-1-butanol has been studied by laser-induced fluorescence, UV and IR fluorescence dip spectroscopy, combined with DFT calculations. Chiral discrimination has been evidenced both in the electronic and vibrational spectra. The homochiral complex with 1-amino-2-propanol displays two distinct kinds of structure: an O-addition complex in which the chromophore adds to the alcohol group of 1-amino-2-propanol, and a N-addition complex in which the chromophore binds to the amino group of 1-amino-2-propanol. In contrast, the heterochiral complex with 1-amino-2-propanol, or both complexes with 2-amino-1-butanol, are of O-addition type. Deeper analysis of the O-addition structures, within the frame of the Natural Bond Orbital theory, has shown that the difference in the vibrational spectrum of the homo- and heterochiral complexes can be rationalised in terms of a different shift from linearity of the intermolecular H-bond, which results in a difference in electron density transfer along the H bond. Last, the study of the vibrational spectrum of the electronic excited state shows that the hydrogen bond network is reinforced upon electronic excitation.