Clifford Paul, Bowen Richard D, Edwards Howell G M, Farwell Dennis W
Division of Chemical and Forensic Sciences, School of Life Sciences, University of Bradford, Bradford, West Yorkshire BD7 1DP, United Kingdom.
Anal Chim Acta. 2007 Aug 29;598(2):268-79. doi: 10.1016/j.aca.2007.07.042. Epub 2007 Jul 22.
The Raman spectra of several pairs of alkenyl methyl ethers of general structure R(1)R(2)C=CR(5)C(R(3)R(4))OCH3 and R(1)R(2)C(OCH3)C(R(5))=CR(3)R(4) (R(1), R(2), R(3), R(4), R(5) = H or C(n)H(2n+1), n = 1-3) are reported and discussed, with a view to establishing whether Raman spectroscopy offers a viable means of distinguishing between these isomeric unsaturated species. Key bands associated with the nu(sp2C-H) and nu(C=C) stretching modes are found to be particularly useful in this connection: R(1)R(2)C=CHCH2OCH3 and R(1)R(2)C(OCH3)CH=CH2 ethers (R(1), R(2) = CH3, C2H5) are easily distinguished on this basis. Differentiation of their lower homologues, R(1)CH=CHCH2OCH3 and R(1)CH(OCH3)CH=CH2 (R(1) = CH3, C2H5, C3H7), by similar means is also quite straightforward, even in cases where cis and trans isomers are possible. Pairs of isomeric ethers, such as CH3CH=C(CH3)CH2OCH3 and CH3CH(OCH3)C(CH3)=CH2, in which the structural differences are more subtle, may also be distinguished with care. Deductions based on bands ascribed to the stretching vibrations are usually confirmed by consideration of the signals associated with the corresponding delta(sp2C-H) deformation vibrations. Even C2H5CH=CHCH(C3H7)OCH3 and C3H7CH=CHCH(C2H5)OCH3 are found to have distinctive Raman spectra, but differentiation of these closely related isomers requires additional consideration of the low wavenumber region.
报道并讨论了几对具有通式R(1)R(2)C=CR(5)C(R(3)R(4))OCH3和R(1)R(2)C(OCH3)C(R(5))=CR(3)R(4)（R(1)、R(2)、R(3)、R(4)、R(5)=H或C(n)H(2n+1)，n=1-3）的烯基甲基醚的拉曼光谱，目的是确定拉曼光谱是否提供了一种区分这些异构不饱和物种的可行方法。发现与ν(sp2C-H)和ν(C=C)伸缩模式相关的关键谱带在此方面特别有用：基于此，R(1)R(2)C=CHCH2OCH3和R(1)R(2)C(OCH3)CH=CH2醚（R(1)、R(2)=CH3、C2H5）很容易区分。通过类似方法区分它们的低级同系物R(1)CH=CHCH2OCH3和R(1)CH(OCH3)CH=CH2（R(1)=CH3、C2H5、C3H7）也相当直接，即使在可能存在顺式和反式异构体的情况下也是如此。结构差异更细微的异构醚对，如CH3CH=C(CH3)CH2OCH3和CH3CH(OCH3)C(CH3)=CH2，也可以小心地区分。基于归属于伸缩振动的谱带的推断通常通过考虑与相应δ(sp2C-H)变形振动相关的信号得到证实。甚至发现C2H5CH=CHCH(C3H7)OCH3和C3H7CH=CHCH(C2H5)OCH3具有独特的拉曼光谱，但区分这些密切相关的异构体需要额外考虑低波数区域。
