37Cl/35Cl-Induced 13C Isotope Shifts in Chlorinated Methanes
37Cl/35Cl-Induced 13C Isotope Shifts in Chlorinated Methanes
复制标题
氯化甲烷中 37Cl/35Cl 诱导的 13C 同位素位移
DOI：
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发表时间：
1995
期刊：
影响因子：
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通讯作者：
W. T. Raynes
中科院分区：
文献类型：
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作者：
N. M. Sergeyev;P. Sándor;N. D. Sergeyeva;W. T. Raynes
在303K到193K温度范围内，用125 MHz共振频率测量了氯代甲烷CH3Cl、CH2Cl2、CHCl3和CCl4的质子耦合~(13)C核磁共振谱，发现有两个因素决定了不同温度下的~(13)C谱形：~(37)Cl/~(35)Cl同位素对~(13)C屏蔽常数的影响和~(13)C-~(37)Cl(或~(35)Cl)自旋相互作用引起的标量弛豫引起的谱线展宽。在仪器分辨率不低于0.1赫兹和数字分辨率优于0.01赫兹的条件下，37Cl/35CL引起的~(13)C化学位移的同位素效应从−3.0到−6.0 ppb/一个37Cl/35Cl置换的幅度随氯的数量减少而减小。在不同温度下测量了CH_3Cl、CH_2Cl_2和CHCl_3的~(37)Cl/~(35)Cl同位素位移，发现在所有情况下，~(13)C-~(13)C-~(37)Cl/~(35)Cl自旋-自旋相互作用引起的~(13)C-~(13)C-~(13)C核磁共振线的额外展宽范围从193K下的CH_3Cl中的小于0.1赫兹到室温下的CCl_4中的约2赫兹，表明所有情况下都与温度有关(−为0.015 ppb/°C)。这些展宽与J2CClT1Cl成正比。由于T1Cl的增加，它们随着温度的升高而增加，在含有35Cl的同位异构体中，它们大约减少11%。~(37)Cl/~(35)Cl同位素位移归因于室温下从C-~(35)Cl到C-~(37)Cl时，C-~(2+)键略微缩短了约4×10−~(-5)A。氯代甲烷的~(13)C核磁共振谱的额外展宽使人们能够估计JCCl耦合常数，范围从CH3Cl中的约11赫兹到CCl4中的约38赫兹。
Proton-coupled 13C NMR spectra of the chlorinated methanes CH3Cl, CH2Cl2, CHCl3, and CCl4 have been measured at 125 MHz resonance frequency in the temperature range from 303 K down to 193 K. Two factors were found to determine the 13C lineshapes at different temperatures: 37Cl/35Cl isotope effects on the 13C shielding constants and line broadenings due to scalar relaxation arising from 13C-37Cl (or 35Cl) spin-spin interactions. With instrumental resolution not worse than 0.1 Hz at all temperatures used and with digital resolution better than 0.01 Hz, 37Cl/35Cl-induced isotope effects on 13C chemical shifts were found ranging from −3.0 to −6.0 ppb per one 37Cl/35Cl replacement decreasing in magnitude with the number of chlorines. 37Cl/35Cl isotope shifts were measured for CH3Cl, CH2Cl2, and CHCl3, at different temperatures, revealing in all cases a temperature dependence of about −0.015 ppb/°C. Additional broadenings of the 13C NMR lines due to 13C-37Cl/35Cl spin-spin interactions range from less than 0.1 Hz in CH3Cl at 193 K to about 2 Hz in CCl4 at ambient temperatures. These broadenings are proportional to J2CClT1Cl. They increase with temperature due to increases of T1Cl and they are of approximately 11% less in isotopomers containing 35Cl. The 37Cl/35Cl isotope shifts are attributed to the very slight shortening of CCl bonds by about 4 × 10−5 A at room temperature on going from C-35Cl to C-37Cl. Additional broadenings in the 13C NMR spectra of chlorinated methanes allow one to estimate JCCl coupling constants ranging from approximately 11 Hz in CH3Cl to approximately 38 Hz in CCl4.