# Probing Hydrogen-Bonding Preferences and Methyl Internal Rotation in Sotolon and Sotolon-(H2O)1,2

## TL;DR

This study explores how water interacts with sotolon and its hydrates using microwave spectroscopy and theory.

## Contribution

The novel contribution is the detailed investigation of hydration effects on sotolon's conformation and methyl rotation.

## Key findings

- Sotolon's conformation is stabilized by an intramolecular hydrogen bond.
- Water forms hydrogen-bonded cycles in hydrated sotolon complexes.
- Hydration modulates the methyl internal rotation barrier in sotolon.

## Abstract

Sotolon is a chiral furanone derivative featuring three distinct oxygen atoms at carbonyl, hydroxyl, and cyclic ether groups that can serve as hydrogen-bond acceptor sites, making it an ideal model system for probing water’s preferential interactions with competing functional groups. In this study, the rotational spectrum of sotolon and its microsolvated complexes, representing the early stages of hydration, was investigated using chirped-pulse Fourier transform microwave (CP-FTMW) spectroscopy. The conformational landscape of sotolon is dominated by a single conformer stabilized by an intramolecular O–H···O=C hydrogen bond. During hydration, water molecules disrupt this interaction by forming closed hydrogen-bonded cycles, resulting in mono- and dihydrated complexes. High-level theoretical calculations underscore the central role of electrostatic interactions in stabilizing these hydrated structures. Furthermore, A/E splittings observed in the rotational spectrum, arising from the internal rotation of one of sotolon’s methyl groups, provide insight into how hydration modulates the methyl internal rotation barrier.