通过中性配体（Ne, Ar, N2）与C6H7O+弱结合复合物的红外光解光谱，研究了孤立的质子化苯酚的结构异构体。光谱在O-H和C-H伸缩振动基本频率附近显示了至少两种C6H7O+异构体的明确特征，包括氧离子O-C6H7O+和芳香环上的正离子o/p-C6H7O+。质子化在meta和ipso位置未被观察到。最稳定的C6H7O+−L二聚体结构以分子间氢键为特征，这些氢键存在于L和O-C6H7O+及o/p-C6H7O+的OH基团之间。通过零溶剂相互作用外推，获得了裸露的O-C6H7O+和o/p-C6H7O+的可靠振动频率。B3LYP和MP2计算与实验光谱和外推的单体频率相吻合，阐明了质子化对苯酚结构性质的影响，并提供了在亲电芳香取代反应中OH基团活化和ortho/para导向性质的敏感探针。
摘要：
Structural isomers of isolated protonated phenol (C6H7O+) are characterized by infrared (IR) photodissociation spectroscopy of their weakly bound complexes with neutral ligands L (L = Ne, Ar, N2). IR spectra of C6H7O+−L recorded in the vicinity of the O−H and C−H stretch fundamentals carry unambiguous signatures of at least two C6H7O+ isomers: the identified protonation sites of phenol include the O atom (oxonium ion, O-C6H7O+) and the C atoms of the aromatic ring in the ortho and/or para position (carbenium ions, o/p-C6H7O+). In contrast, protonation at the meta and ipso positions is not observed. The most stable C6H7O+−L dimer structures feature intermolecular H-bonds between L and the OH groups of O-C6H7O+ and o/p-C6H7O+. Extrapolation to zero solvation interaction yields reliable experimental vibrational frequencies of bare O-C6H7O+ and o/p-C6H7O+. The interpretation of the C6H7O+−L spectra, as well as the extrapolated monomer frequencies, is supported by B3LYP and MP2 calculations using the 6-311G(2df,2pd) basis. The spectroscopic and theoretical results elucidate the effect of protonation on the structural properties of phenol and provide a sensitive probe of the activating and ortho/para directing nature of the OH group observed in electrophilic aromatic substitution reactions.
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