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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Spectroscopic and theoretical investigation of (R)-3-methylcyclopentanone. The effect of solvent and temperature on the distribution of conformers
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Spectroscopic and theoretical investigation of (R)-3-methylcyclopentanone. The effect of solvent and temperature on the distribution of conformers

机译：（R）-3-甲基环戊酮的光谱和理论研究。溶剂和温度对构象异构体分布的影响

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摘要

Temperature-dependent electronic circular dichroism (CD) spectra are reported for (R)-(+)-3-methylcyclopentanone (R3MCP) in 34 solvents. Analysis of these data yielded the enthalpy and entropy differences between axial methyl and equatorial methyl conformers, the dominant conformers for R3MCP. The weakly absorbing n -> pi* transition exhibited a decrease in lambda(max) as the solvent polarity increased. Vibrational CD fine structure of the n -> pi* transition was observed in the gas phase in addition to several of the solvents. Vapor-phase CD spectra were compared to both the solution-phase spectra and theoretical calculations of the axial and equatorial methyl conformers. Optical rotation (OR) measurements for R3MCP in cyclohexane solution in the visible region showed excellent agreement with OR DFT calculations of the equatorial and axial methyl conformers. Density functional calculations with B3LYP and the 6-13G(*) and aug-cc-pVDZ basis sets, which incorporate the solvent dielectric constant, yielded trends in thermodynamic quantities as a function of polarity and solvent dipole moments that are only weakly or not observed in experiments.
机译：报告了在34种溶剂中（R）-（+）-3-甲基环戊酮（R3MCP）的温度依赖性电子圆二色性（CD）光谱。对这些数据的分析得出了轴向甲基和赤道甲基构象异构体（R3MCP的主要构象异构体）之间的焓和熵差。随着溶剂极性的增加，弱吸收n-> pi *跃迁的lambda（max）减小。除了几种溶剂外，在气相中还观察到了n-> pi *跃迁的振动CD精细结构。将气相CD光谱与溶液相光谱以及轴向和赤道甲基构象异构体的理论计算进行了比较。可见区中环己烷溶液中R3MCP的旋光度（OR）测量与赤道和轴向甲基构象异构体的OR DFT计算非常吻合。使用B3LYP以及6-13G（*）和aug-cc-pVDZ基集进行的密度泛函计算，结合了溶剂的介电常数，得出了热力学量随极性和溶剂偶极矩而变化的趋势，而这种变化仅在微弱的条件下或未观察到在实验中。

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