Departamento de Química Física y Química Inorgánica - IU CINQUIMA, Facultad de Ciencias, Universidad de Valladolid, E-47011 Valladolid, Spain.
Phys Chem Chem Phys. 2019 Feb 13;21(7):3676-3682. doi: 10.1039/c8cp04455d.
Two conformers of cyclohexanol and the cyclohexanol-water adduct have been characterized in a jet expansion using rotational spectroscopy. In the gas phase, cyclohexanol adopts an equatorial position for the hydroxyl group, with the two conformers differing in the orientation of the hydroxylic hydrogen, either gauche or trans with respect to the aliphatic hydrogen at C(1). Axial cyclohexanol was not detected in the jet. The transitions of the gauche conformer are split into two component lines due to the tunneling effect of the O-H internal rotation, which connects two equivalent gauche minima. The tunneling splitting in the vibrational ground state has been determined to be ΔE0+0- = 52(2) GHz. From this splitting, the inversion barriers connecting the two equivalent gauche conformers have been determined using a flexible model to be B2 = 377 cm-1. A single isomer is detected for the cyclohexanol-water dimer, in which the water molecule acts as a proton donor to the equatorial gauche ring. The presence of torsional tunneling in the adduct suggests a concerted large-amplitude-motion in which the internal rotation in the ring is accompanied by a torsion of the water molecule, to produce an equivalent enantiomer. The torsional tunneling in the adduct is reduced to ΔE0+0- = 32.7(4) GHz and the potential barrier in the complex increases to B2 = 494 cm-1.
已在喷射膨胀中使用旋转光谱学对环己醇和环己醇-水加合物的两种构象进行了表征。在气相中，环己醇的羟基采取赤道位置，两种构象在羟基氢的取向方面有所不同，要么是 gauche 要么是 trans 相对于 C(1)处的脂肪氢。轴向环己醇在射流中未被检测到。gauche 构象的跃迁由于 O-H 内旋转的隧道效应而分裂成两个分量线，该隧道效应连接两个等效的 gauche 最小值。振动基态中的隧道分裂已被确定为 ΔE0+0- = 52(2)GHz。根据该分裂，使用柔性模型确定了连接两个等效 gauche 构象的反转势垒，B2 = 377cm-1。环己醇-水二聚体检测到单个异构体，其中水分子充当赤道 gauche 环的质子供体。加合物中存在扭转隧道表明协同的大幅度运动，其中环内的内部旋转伴随着水分子的扭转，以产生等效的对映体。加合物中的扭转隧道降低到 ΔE0+0- = 32.7(4)GHz，复合物中的势垒增加到 B2 = 494cm-1。
