Krupa Justyna, Wierzejewska Maria, Nunes Cláudio M, Fausto Rui
Faculty of Chemistry, University of Wrocław, Joliot-Curie 14, 50-383 Wrocław, Poland.
Department of Chemistry, University of Coimbra, 3004-535 Coimbra, Portugal.
J Chem Phys. 2014 Mar 14;140(10):105102. doi: 10.1063/1.4867896.
A matrix isolation study of the infrared spectra and structure of anethole (1-methoxy-4-(1-propenyl)benzene) has been carried out, showing the presence of two E conformers (AE1, AE2) of the molecule in the as-deposited matrices. Irradiation using ultraviolet-tunable laser light at 308-307 nm induced conformationally selective phototransformations of these forms into two less stable Z conformers (AZ1, AZ2). The back reactions were also detected upon irradiation at 301 nm. On the whole, the obtained results allow for full assignment of the infrared spectra of all the four experimentally observed anethole isomers and showed that the narrowband UV-induced E-Z photoisomerization is an efficient and selective way to interconvert the two isomers of anethole into each other, with conformational discrimination. Photolysis of anethole was observed as well, with initial methoxyl O-C bond cleavage and formation of CH3 and p-propenylphenoxy (AR) radicals, followed by radical recombination to form 2-methyl-4-propenyl-2,4-cyclohexadienone, which subsequently undergoes ring-opening generating several conformers of long-chain conjugated ketenes. Interpretation of the experimental observations was supported by density functional theory (B3LYP and B2PLYD) calculations.
对茴香脑（1-甲氧基-4-（1-丙烯基）苯）的红外光谱和结构进行了基质隔离研究，结果表明在刚沉积的基质中该分子存在两种E构象异构体（AE1、AE2）。使用308 - 307 nm的紫外可调谐激光进行辐照，可使这些构象选择性地光转化为两种较不稳定的Z构象异构体（AZ1、AZ2）。在301 nm辐照时也检测到了逆向反应。总体而言，所获得的结果能够对所有四种实验观察到的茴香脑异构体的红外光谱进行完整归属，并表明窄带紫外诱导的E - Z光异构化是一种有效且选择性的方法，可使茴香脑的两种异构体相互转化，并具有构象区分性。还观察到了茴香脑的光解，首先是甲氧基的O - C键断裂并形成甲基和对丙烯基苯氧基（AR）自由基，随后自由基重组形成2 - 甲基 - 4 - 丙烯基 - 2,4 - 环己二烯酮，该物质随后开环生成几种长链共轭烯酮的构象异构体。密度泛函理论（B3LYP和B2PLYD）计算支持了对实验观察结果的解释。
