Spectroscopic and Theoretical Investigation of (R)-3-Methylcyclopentanone. The Effect of Solvent and Temperature on the Distribution of Conformers

详细信息    查看全文

• 作者：Watheq Al-Basheer ; Richard M. Pagni ; Robert N. Compton
• 刊名：Journal of Physical Chemistry A
• 出版年：2007
• 出版时间：March 29, 2007
• 年：2007
• 卷：111
• 期：12
• 页码：2293 - 2298
• 全文大小：172K
• 年卷期：v.111,no.12(March 29, 2007)
• ISSN：1520-5215

文摘

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 betweenaxial methyl and equatorial methyl conformers, the dominant conformers for R3MCP. The weakly absorbingn mages/entities/rarr.gif"> mages/gifchars/pi.gif" BORDER=0 >* transition exhibited a decrease in mages/gifchars/lambda.gif" BORDER=0 >_max as the solvent polarity increased. Vibrational CD fine structureof the n mages/entities/rarr.gif"> mages/gifchars/pi.gif" BORDER=0 >* transition was observed in the gas phase in addition to several of the solvents. Vapor-phaseCD spectra were compared to both the solution-phase spectra and theoretical calculations of the axial andequatorial methyl conformers. Optical rotation (OR) measurements for R3MCP in cyclohexane solution inthe visible region showed excellent agreement with OR DFT calculations of the equatorial and axial methylconformers. Density functional calculations with B3LYP and the 6-13G^* and aug-cc-pVDZ basis sets, whichincorporate the solvent dielectric constant, yielded trends in thermodynamic quantities as a function of polarityand solvent dipole moments that are only weakly or not observed in experiments.