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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >FTIR Investigation of the Fluorocyclohexane Ring Inversion in Liquid Kr
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FTIR Investigation of the Fluorocyclohexane Ring Inversion in Liquid Kr

机译：液态Kr中氟环己烷环的FTIR研究

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摘要

Midinfrared spectra of solutions of fluorocyclohexane, C_6H_(11)F, in liquid Kr (LKr) have been investigated at temperatures between 120 and 188 K. Three temperature intervals are distinguished for the equatorial (e) <-> axial (a) conformational relaxation. At temperatures below 141 K the rate of conformational equilibration is negligible and the population ratio of the conformers is "frozen", while at temperatures above 151 K the equilibrium is established nearly instantaneously. In the intermediate temperature interval, the relaxation times are such that the equilibration can be followed using FTIR spectroscopy. From spectra recorded between 151 and 188 K the standard enthalpy difference ΔH° in LKr was determined to be 1.3 (4) kJ mol~(-1). Between 141 and 151 K, and starting from solutions with nonequilibrium conformer populations, the conformational relaxation was studied as a function of time. From these data, the enthalpy ΔH and entropy ΔS of activation for the a- to e-conformer interconversion were found to be 37.8 (12) kJ mol~(-1) and -30 (9) J mol~(-1) K~(-1), respectively. From the kinetic data, the extinction coefficients ratio ∈_e/∈_a for the v_(21) conformational doublet was determined to be 0.38 (4). The standard entropy difference ΔS° was determined using this extinction coefficient ratio, yielding a value of 1.14 (11) J mol~(-1) K~(-1), and was also determined from the temperature dependence of the infrared band areas, yielding a value of 1.0 (6) J mol~(-1) K~(-1). the results are discussed in light of literature data and in light of Monte Carlo free energy perturbation calculations, which yield information on the difference in solvation enthalpy and difference in solvation entropy of this species studied.
机译：在120至188 K之间的温度下研究了氟环己烷C_6H_（11）F在液体Kr（LKr）中的中红外光谱。为赤道（e）<->轴向（a）构象弛豫确定了三个温度区间。在低于141 K的温度下，构象平衡的速率可忽略不计，并且构象异构体的总体比率为“冻结”，而在高于151 K的温度下，几乎立即建立平衡。在中间温度区间中，弛豫时间使得可以使用FTIR光谱法进行平衡。根据在151和188 K之间记录的光谱，LKr中的标准焓差ΔH°被确定为1.3（4）kJ mol〜（-1）。在141 K和151 K之间，从具有非平衡构象体总体的溶液开始，研究了构象弛豫随时间的变化。根据这些数据，发现α-构象异构体互变的活化焓ΔH和活化熵ΔS分别为37.8（12）kJ mol〜（-1）和-30（9）J mol〜（-1）K 〜（-1）。根据动力学数据，确定v_（21）构象对偶峰的消光系数比∈_e/∈_a为0.38（4）。使用该消光系数比率确定标准熵差ΔS°，得出的值为1.14（11）J mol〜（-1）K〜（-1），并且还取决于红外波段区域的温度依赖性，得出的值为1.0（6）J mol〜（-1）K〜（-1）。根据文献数据和蒙特卡洛自由能扰动计算对结果进行了讨论，这些结果提供了有关该物种的溶剂化焓差和溶剂化熵差的信息。

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