Structures of (3n-Crown-n)-Phenol (n = 4, 5, 6, 8) Host-Guest Complexes: Formation of a Uniquely Stable Complex for n = 6 via Collective Intermolecular Interaction.
Structures of crown-phenol 1:1 host-guest complexes, 3n-crown-n [12C4(n = 4), 15C5(n = 5), 18C6(n = 6), 24C8(n = 8)], in the gas phase have been studied by various laser spectroscopic methods. The S1-S0 electronic spectra identified 3, 2, 1, and 2 isomers for the complexes of 12C4, 15C5, 18C6, and 24C8, respectively, suggesting that only 18C6-phenol forms one uniquely stable complex. The IR spectra in the phenolic OH and CH stretch regions indicate that these complexes form the O···HO hydrogen bond, and the benzene ring is involved in the complex formation. Theoretical analysis with molecular mechanics and density functional theory calculations also supports one considerably stable isomer for 18C6-phenol. The most stable 18C6-phenol isomer is largely stabilized through collective intermolecular interaction consisting of O···HO hydrogen bond, CH···π, and O···HC(aromatic) so that phenol is inserted into the cavity of a particular conformation of 18C6 like a "lock and key".
Department of Chemistry, Graduate School of Science, Hiroshima University, Higashi-Hiroshima 739-8526, Japan.
Ryoji
R
Kusaka
Department of Chemistry, Graduate School of Science, Hiroshima University, Higashi-Hiroshima 739-8526, Japan.
Yoshiya
Y
Inokuchi
Department of Chemistry, Graduate School of Science, Hiroshima University, Higashi-Hiroshima 739-8526, Japan.
Takeharu
T
Haino
Department of Chemistry, Graduate School of Science, Hiroshima University, Higashi-Hiroshima 739-8526, Japan.
Takayuki
T
Ebata
crown ethers; host−guest complex; lock and key; molecular recognition; phenol