Cummings Charlotte N, Walker Nicholas R
Chemistry- School of Natural and Environmental Sciences, Newcastle University, Bedson Building, Newcastle-upon-Tyne NE1 7RU, U.K.
J Phys Chem A. 2025 May 29;129(21):4644-4653. doi: 10.1021/acs.jpca.5c01281. Epub 2025 May 14.
Rotational spectra of one conformer of a 2-ethylfuran···HO complex and two conformers of the isolated 2-ethylfuran molecule have been recorded by chirped-pulse Fourier transform microwave spectroscopy. The species were probed while entrained within a gas sample undergoing supersonic expansion. The spectra of five isotopologues of the complex have been analyzed to yield rotational (, , ) and centrifugal distortion constants (, , ) allowing structural parameters to be determined by fitting to the experimentally determined moments of inertia. Quantum chemical calculations have been performed to support the interpretation of the experimental results and gain further insights. 2-Ethylfuran is shown to adopt C symmetry within the observed conformer of 2-ethylfuran···HO with the length of the hydrogen bond, (H···O1), which connects HO with 2-ethylfuran determined to be 2.0950(42) Å in the geometry. The geometry of the hydrogen bonding interaction deviates from linearity such that the ∠(O-H···O1) angle (where O and O1 are the oxygen atoms of water and furan, respectively) is 167.69(16)° in the geometry. The experimental and theoretical results thus imply the presence of a weak interaction between the oxygen of HO and the ethyl group within the observed conformer of 2-ethylfuran···HO. Evidence is presented to suggest that the C conformer of the isolated 2-ethylfuran molecule is lower in energy than the C conformer implying that the energy ordering of the two lowest-energy conformers of 2-ethylfuran reverses when the isolated molecule is hydrated by a single HO molecule.
利用啁啾脉冲傅里叶变换微波光谱法记录了2-乙基呋喃···HO络合物一种构象异构体以及孤立的2-乙基呋喃分子两种构象异构体的转动光谱。这些物种在被夹带于经历超声速膨胀的气体样品中时受到探测。对该络合物五种同位素变体的光谱进行了分析，以得出转动常数（A、B、C）和离心畸变常数（D J、D JK、D K），从而通过拟合实验测定的转动惯量来确定结构参数。已进行量子化学计算以支持对实验结果的解释并获得进一步的见解。结果表明，在2-乙基呋喃···HO的观测构象异构体中，2-乙基呋喃采取C 2v对称性，连接HO与2-乙基呋喃的氢键长度（H···O1）在C 2v几何构型中确定为2.0950(42) Å。氢键相互作用的几何构型偏离线性，使得∠(O-H···O1)角（其中O和O1分别是水和呋喃的氧原子）在C 2v几何构型中为167.69(16)°。因此，实验和理论结果表明，在2-乙基呋喃···HO的观测构象异构体中，HO的氧与乙基之间存在弱相互作用。有证据表明，孤立的2-乙基呋喃分子的C 2v构象异构体能量低于C s构象异构体，这意味着当孤立分子被单个HO分子水合时，2-乙基呋喃两个最低能量构象异构体的能量顺序会反转。
