Preparation and NMR studies of 3-selenaheptadecanoic and 4-selenaoctadecanoic acid, RSe(CH2)nC(O)OH (R = C14H29, n = 1 and 2), and their methyl esters
作者:Khaled I. Doudin、Rolf K. Berge、Nils Åge Frøystein、Jon Songstad
DOI:10.1039/a909142d
日期:——
The synthesis of the title compounds and their precursor, ditetradecyl diselenide, R2Se2, in high yield and of high purity is described. A 600 MHz 1H NMR study at 298 K in CDCl3 and CCl4 has revealed that 4-selenaoctadecanoic acid displays a singlet for the 2- and 3-H2 protons integrating for four protons, while the corresponding sulfur compound shows the expected doublet of triplets. Only in C6D6, and partly in (CD3)2SO, are the signals due to these protons sufficiently separated to give two triplets. No obvious relationship between the form of the spectra and any of the usual solvent parameters could be found. The particular form of the 1H NMR spectrum in CDCl3 and CCl4 was found to be independent of the concentration, i.e. the monomer∶dimer ratio. A temperature study has revealed that while the signal due to the 3-H2 protons is essentially independent of the temperature, the 2-H2 proton signal is shifted downfield with decreasing temperature, causing the close-lying signals to be indistinguishable in the 290–310 K range. NMR spectra of the carboxylic OH group and IR spectra of the carbonyl group of dilute solutions of 3-selena- and 3-thiaheptadecanoic acids in CCl4 suggest that the monomers of these acids exist predominantly as 4-membered cyclic species with Se(S)⋯OC or Se(S)⋯O(H) intramolecular interactions.
本文介绍了高产率、高纯度合成标题化合物及其前体--二硒化双十四烷基 R2Se2 的方法。在 298 K 时,在 CDCl3 和 CCl4 中进行的 600 MHz 1H NMR 研究显示,4-硒代十八烷酸的 2-H2 和 3-H2 质子显示出单重,四个质子整合在一起,而相应的硫化合物则显示出预期的双重三重。只有在 C6D6 中,以及部分在 (CD3)2SO 中,这些质子的信号才会充分分离,从而产生两个三重信号。找不到光谱形式与任何常见溶剂参数之间的明显关系。研究发现,CDCl3 和 CCl4 中 1H NMR 光谱的特定形式与浓度(即单体∶二聚体比率)无关。温度研究表明,虽然 3-H2 质子信号基本上与温度无关,但 2-H2 质子信号会随着温度的降低而下移,导致在 290-310 K 范围内,相邻信号无法区分。3-selena- 和 3-thiaheptadecanoic acids 在 CCl4 中稀释溶液的羧基 OH 基 NMR 光谱和羰基 IR 光谱表明,这些酸的单体主要以具有 Se(S)⋯OC 或 Se(S)⋯O(H) 分子内相互作用的 4 元环状结构存在。