THE r$_0$ STRUCTURAL PARAMETERS OF EQUATORIAL BROMOCYCLOBUTANE, CONFORMATIONAL STABILITY FROM TEMPERATURE DEPENDENT INFRARED SPECTRA OF XENON SOLUTIONS, AND VIBRATIONAL ASSIGNMENTS
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Date
2009
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Publisher
Ohio State University
Abstract
Variable temperature (-55 to $-100\,^{irc}\mathrm{C}$) studies of the infrared spectra (4000-400 cm$^{-1}$) of bromocyclobutane, c-C$_4$H$_7$Br dissolved in liquid xenon have been carried out. The infrared spectrum (4000-100 cm$^{-1}$) of the gas has also been recorded. The enthalpy difference between the more stable equatorial conformer and the axial form, has been determined to be 372 $\pm$ 34 cm$^{-1}$ . This experimental value of $\Delta$H is much lower than the average MP2(full) {\em ab initio} predicted value of 521 $\pm$ 87 cm$^{-1}$. The percentage of the axial conformer present at ambient temperature is estimated to be 14 $\pm$ 1$\%$. By utilizing previously reported microwave rotational constants for the equatorial conformer combined with {\em ab initio} MP2(full)/6-311+G(d,p) predicted structural values, adjusted r$_0$ parameters have been obtained. The determined heavy atom structural parameters for this conformer are with distances($\AA$) C$_\alpha$-Br = 1.942(3), C$_\alpha$-C$_\beta$ = 1.541(5), C$_\gamma$-C$_\beta$ = 1.552(3)$\AA$ and angles in degrees $\angle$C$_\beta$C$_\alpha$Br = 118.4(5), $\angle$C$_\beta$C$_\alpha$C$_\beta$ = 89.7(5), $\angle$C$_\gamma$C$_\beta$C$_\alpha$ = 86.8(5), $\angle$C$_\beta$C$_\gamma$C$_\beta$ = 88.9(5) and $\tau$C$_\gamma$C$_\beta$C$_\beta$C$_\alpha$ = 29.8$(5)\,^{irc}{\rm}$. The results will be discussed and compared to the corresponding properties of some similar molecules.
Description
Author Institution: DEPARTMENT OF CHEMISTRY, UNIVERSITY OF MISSOURI-KANSAS CITY, KANSAS CITY, MO 64110,USA; DEPARTMENT OF CHEMISTRY AND BIOCHEMISTRY, COLLEGE OF CHARLESTON, CHARLESTON, SC 29424, USA