Structural study of 1- and 2-naphthol: new insights into the non-covalent H–H interaction in cis -1-naphthol

• Published in: Physical chemistry chemical physics : PCCP Vol. 24; no. 6; pp. 3722 - 3732
• Main Authors: Hazrah, Arsh S., Nanayakkara, Sadisha, Seifert, Nathan A., Kraka, Elfi, Jäger, Wolfgang
• Format: Journal Article
• Language: English
• Published: England Royal Society of Chemistry 09.02.2022
• Subjects: Electronic structure; Isomerism; Isomers; Naphthol; Naphthols; Quantum Theory
• ISSN: 1463-9076; 1463-9084; 1463-9084
• DOI: 10.1039/D1CP05632H

Previous microwave studies of naphthol monomers were supplemented by measuring spectra of all 13 C mono-substituted isotopologues of the cis - and trans -conformers of 1-naphthol and 2-naphthol in their natural abundances. The resulting data were utilized to determine substitution structures and so-called semi-experimental effective structures. Results from electronic structure calculations show that the OH group of cis -1-naphthol points ≈6° out of plane, which is consistent with the inertial defect data of cis - and trans -1-naphthol. The non-planarity of cis -1-naphthol is a result of a close-contact H-atom–H-atom interaction. This type of H–H interaction has been the subject of much controversy in the past and we provide here an in-depth theoretical analysis of it. The naphthol system is particularly well-suited for such analysis as it provides internal standards with its four different isomers. The methods used include quantum theory of atoms in molecules, non-covalent interactions, independent gradient model, local vibrational mode, charge model 5, and natural bond orbital analyses. We demonstrate that the close-contact H–H interaction is neither a purely attractive nor repulsive interaction, but rather a mixture of the two.