Balabin Roman M
Department of Chemistry and Applied Biosciences, ETH Zurich, 8093 Zurich, Switzerland.
J Phys Chem A. 2009 Feb 12;113(6):1012-9. doi: 10.1021/jp809639s.
Conformation equilibrium in normal pentane (C(5)H(12)) was studied by the low-temperature gas-phase Raman spectroscopy method. A special retroreflecting multipass cell was constructed. Gas-phase (vapor) spectra were recorded in the temperature region of -130.3 to -23.1 degrees C and in the spectral range below 500 cm(-1). The peaks of trans-trans (399.0 cm(-1)), trans-gauche (328.9 cm(-1)), and gauche(+)-gauche(+) (267.1 cm(-1)) conformers (rotamers) of n-pentane were assigned using quantum chemistry data (MP2 and B3LYP methods with aug-cc-pVTZ basis set). The contour of each line was deconvoluted using ab initio data to obtain precise total integral intensity. The intensities at different temperatures were used to evaluate the enthalpy (energy) difference between trans-gauche and trans-trans (DeltaH(tg) = 618 +/- 6 cal/mol), and gauche(+)-gauche(+) and trans-trans (DeltaH(g+g+) = 940 +/- 20 cal/mol) conformers. Normal butane (n-butane) measurements under similar experimental conditions have been taken to understand the chain length influence. The C(4)H(10) enthalpy difference value has been evaluated (DeltaH(g) = 660 +/- 22 cal/mol). The results are compared with published experimental and theoretical data. The data presented here can be used as a reference for quantum chemistry calculations of conformation equilibrium in n-butane and n-pentane.
采用低温气相拉曼光谱法研究了正戊烷（C₅H₁₂）的构象平衡。构建了一种特殊的后向反射多程池。在-130.3至-23.1℃的温度范围内以及低于500 cm⁻¹的光谱范围内记录气相（蒸汽）光谱。利用量子化学数据（采用aug-cc-pVTZ基组的MP2和B3LYP方法）对正戊烷的反式-反式（399.0 cm⁻¹）、反式-gauche式（328.9 cm⁻¹）和gauche(+)-gauche(+)（267.1 cm⁻¹）构象异构体（旋转异构体）的峰进行了归属。使用从头算数据对每条谱线的轮廓进行去卷积以获得精确的总积分强度。利用不同温度下的强度来评估反式- gauche式与反式-反式（ΔH(tg) = 618 ± 6 cal/mol）以及gauche(+)-gauche(+)与反式-反式（ΔH(g+g+) = 940 ± 20 cal/mol）构象异构体之间的焓（能量）差。在相似实验条件下对正丁烷（n-丁烷）进行了测量以了解链长的影响。评估了C₄H₁₀的焓差值（ΔH(g) = 660 ± 22 cal/mol）。将结果与已发表的实验和理论数据进行了比较。此处给出的数据可作为正丁烷和正戊烷构象平衡量子化学计算的参考。
