EXPERIMENTAL-DETERMINATION OF THE CONFORMATIONAL FREE-ENERGY - ENTHALPY, AND ENTROPY DIFFERENCES FOR ALKYL-GROUPS IN ALKYLCYCLOHEXANES BY LOW-TEMPERATURE C-13 MAGNETIC-RESONANCE SPECTROSCOPY
EXPERIMENTAL-DETERMINATION OF THE CONFORMATIONAL FREE-ENERGY - ENTHALPY, AND ENTROPY DIFFERENCES FOR ALKYL-GROUPS IN ALKYLCYCLOHEXANES BY LOW-TEMPERATURE C-13 MAGNETIC-RESONANCE SPECTROSCOPY
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DOI：
10.1039/p29800000255
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发表时间：
1980-01-01
期刊：
影响因子：
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通讯作者：
EVERETT, JR
中科院分区：
文献类型：
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作者：
BOOTH, H;EVERETT, JR
13 C N.m.r. [Me-13 C]甲基环己烷、[α-13 C]-异丙基环己烷、顺式-1-乙基-4-甲基环己烷、顺式-1-异丙基-4-甲基环己烷和顺式-1-乙基-4-异丙基环己烷在CFCl 3-CDCl 3中的溶液在低温下的研究已经得到了烷基环己烷中甲基、乙基和异丙基基团的构象焓差和构象熵差。对于-ΔH°，以kcal mol-1为单位获得的平均值分别为1.75（Me）、1.60（Et）和1.52（Pri）;对于ΔS°，以cal mol-1 K-1为单位获得的平均值分别为-0.03（Me）、0.64（Et）和2.31（Pri）。确定的值是在良好的协议与计算的Allinger组的气相，使用基于经典力学的方法。由于-ΔH°和ΔS°值的相反趋势，在300 K时-ΔG°值的顺序，即Pri > Et > Me，在低于ca.四万
13 C N.m.r. studies at low temperatures of solutions in CFCl3–CDCl3 of [Me-13C]methylcyclohexane, [α-13C]-isopropylcyclohexane, cis-1-ethyl-4-methylcyclohexane, cis-1-isopropyl-4-methylcyclohexane, and cis-1-ethyl-4-isopropylcyclohexane have yielded conformational enthalpy differences and conformational entropy differences for methyl, ethyl, and isopropyl groups in alkylcyclohexanes. For –ΔH°, the averaged values obtained, in kcal mol–1, were 1.75 (Me), 1.60 (Et), and 1.52 (Pri); for ΔS°, the averaged values, in cal mol–1 K–1, were –0.03 (Me), 0.64 (Et), and 2.31 (Pri). The determined values are in good agreement with those calculated by the Allinger group for the gas phase, using a method based on classical mechanics. As a result of the opposing trends for –ΔH° and ΔS° values, the sequence of –ΔG° values at 300 K, namely Pri > Et > Me, is reversed at temperatures below ca. 40 K.