Files in this item

FilesDescriptionFormat

application/vnd.openxmlformats-officedocument.presentationml.presentation

application/vnd.openxmlformats-officedocument.presentationml.presentation1121552.pptx (52MB)
PresentationMicrosoft PowerPoint 2007

application/pdf

application/pdf3056.pdf (23kB)
AbstractPDF

Description

Title:INFRARED SPECTRA OF C2H4BR AND C2H4I IN SOLID PARA-HYDROGEN: BRIDGED OR OPEN STRUCTURE?
Author(s):Chen, Yu-Hsuan
Contributor(s):Lee, Yuan-Pern
Subject(s):Vibrational structure/frequencies
Abstract:The electrophilic addition of halogens to alkenes is important in organic synthesis. The structure of the reaction intermediate, haloalkyl radical, plays an important role in the stereo specificity of the addition reaction. The simplest intermediate, haloethyl radical \chem{C_2H_4X}, has two possible geometries: an open (classical) structure and a bridged structure. However, which structure is more stable is controversial because several calculations yield varied results. Experiments using time-resolved X-ray diffraction\footnote{H. Ihee, M. Lorenc, T. K. Kim, Q. Y. Kong, M. Cammarata, J. H. Lee, S. Bratos, M. Wulff, \textit{Science}. 2005, {\bf 309}, 1223.} and UV absorption\footnote{A. Kalume, L. George, A. D. Powell, R. Dawes, S. A. Ried, \textit{J. Phys. Chem. A}. 2014, {\bf 118}, 6838.} indicated that \chem{C_2H_4I} has a briedged structure, but our results of Cl + \chem{C_2H_4} in solid \textit{para}-hydrogen (\textit{p}-\chem{H_2}) indicated that \chem{C_2H_4Cl} has an open structure.\footnote{J. C. Amicangelo, B. Golec, M. Bahou, Y. P. Lee, \textit{Phys. Chem. Chem. Phys}. 2012, {\bf 14}, 1014.} Even though experiments in noble-gas matrices suggest that \chem{C_2H_4Br} is open,\footnote{A. Kalume, L. George, P. Z. El-Khoury, A. N. Tarnovsky, S. A. Reid, \textit{J. Phys. Chem. A}. 2010, {\bf 114}, 9919.} whereas \chem{C_2H_4I} is bridged,\footnote{L. George, A. Kalume, S. A. Reid, \textit{Chem. Phys. Lett}. 2012, {\bf 554}, 86.} the spectral evidence remains uncertain. We took advantage of the diminished cage effect of \textit{p}-\chem{H_2} to investigate the infrared (IR) spectra of \chem{C_2H_4Br} and \chem{C_2H_4I} by irradiating \textit{p}-\chem{H_2} matrices containing \chem{C_2H_4} and \chem{Br_2} or \chem{I_2} with light at varied wavelengths. New spectral lines were grouped according to their behavior upon subsequent annealing and secondary photolysis. The assignments were derived on comparison with scaled vibrational wavenumbers and IR intensities calculated with the B3LYP/aug-cc-pVTZ-pp method. Our preliminary results indicate that lines at 676.9, 776.7, 1068.1, 1148.0, and 3126.8 \wn are assigned to the 2-bromoethyl radical (\chem{C_2H_4Br}) in an open form, whereas those at 933.7, 1139.0, 1436.8, and 1609.0 \wn to the iodoethyl radical (\chem{C_2H_4I}) in the bridged form. A small amount of \chem{C_2H_4Br_2} and \chem{C_2H_4I_2} was also observed; their stereochemistry will also be discussed.
Issue Date:06/22/18
Publisher:International Symposium on Molecular Spectroscopy
Citation Info:APS
Genre:Conference Paper / Presentation
Type:Text
Language:English
URI:http://hdl.handle.net/2142/100487
DOI:10.15278/isms.2018.FE03
Other Identifier(s):FA03
Date Available in IDEALS:2018-08-17
2018-12-12


This item appears in the following Collection(s)

Item Statistics