The interplay of hydrogen bonding and dispersion in phenol dimer and trimer: structures from broadband rotational spectroscopy

Abstract

The structures of the phenol dimer and phenol trimer complexes in the gas phase have been determined using chirped-pulse Fourier transform microwave spectroscopy in the 2–8 GHz band. All fourteen ¹³C and ¹⁸O phenol dimer isotopologues were assigned in natural abundance. A full heavy atom experimental substitution structure was determined, and a least-squares fit ground state r₀ structure was determined by proper constraint of the M06-2X/6-311++g(d,p) ab initio structure. The structure of phenol dimer features a water dimer-like hydrogen bond, as well as a cooperative contribution from inter-ring dispersion. Comparisons between the experimental structure and previously determined experimental structures, as well as ab initio structures from various levels of theory, are discussed. For phenol trimer, a C₃ symmetric barrel-like structure is found, and an experimental substitution structure was determined via measurement of the six unique ¹³C isotopologues. The least-squares fit r_m⁽¹⁾ structure reveals a similar interplay between hydrogen bonding and dispersion in the trimer, with water trimer-like hydrogen bonding and C–H⋯π interactions.