Departamento de Química Física y Química Inorgánica, Facultad de Ciencias, Universidad de Valladolid, E-47011 Valladolid, Spain.
Phys Chem Chem Phys. 2011 Apr 14;13(14):6610-8. doi: 10.1039/c0cp02465a. Epub 2011 Mar 7.
The conformational and structural properties of the inhalational anesthetic isoflurane (1-chloro-2,2,2-trifluoroethyl difluoromethyl ether) have been probed in a supersonic jet expansion using Fourier-transform microwave (FT-MW) spectroscopy. Two conformers of the isolated molecule were identified from the rotational spectrum of the parent and several (37)Cl and (13)C isotopologues detected in natural abundance. The two most stable structures of isoflurane are characterized by an anti carbon skeleton (τ(C(1)-C(2)-O-C(3)) = 137.8(11)° or 167.4(19)°), differing in the trans (AT) or gauche (AG) orientation of the difluoromethyl group. The conformational abundances in the jet were estimated from relative intensity measurements as (AT)/(AG) ≈ 3:1. The structural preferences of the molecule have been rationalized with supporting ab initio calculations and natural-bond-orbital (NBO) analysis, which suggest that the molecule is stabilized by hyperconjugative effects. The NBO analysis of donor-acceptor (LP → σ*) interactions showed that these stereoelectronic effects decrease from the AT to AG conformations, so the conformational preferences can be accounted for in terms of the generalized anomeric effect.
使用傅里叶变换微波（FT-MW）光谱法，在超声速射流膨胀中探测吸入麻醉剂异氟烷（1-氯-2,2,2-三氟乙基二氟甲基醚）的构象和结构性质。从母体的旋转光谱以及在自然界中以天然丰度检测到的几个 (37)Cl 和 (13)C 同位素中，鉴定出游离分子的两种构象。异氟烷的两种最稳定结构的特征是反式碳骨架（τ(C(1)-C(2)-O-C(3)) = 137.8(11)°或 167.4(19)°），不同之处在于二氟甲基基团的反式 (AT) 或 gauche (AG) 取向。通过相对强度测量，从射流中估算出构象丰度为 (AT)/(AG) ≈ 3:1。用支持的从头算计算和自然键轨道（NBO）分析来合理化分子的结构偏好，这表明分子通过超共轭效应稳定。供体-受体（LP → σ*）相互作用的 NBO 分析表明，这些立体电子效应从 AT 构象到 AG 构象减小，因此构象偏好可以根据广义的端基效应来解释。
