Normal coordinate analysis of the vibrational frequencies of ethylene, propylene, cis-2-butene, trans-2-butene, and isobutene

Thc secular equation for the vibrations of ethylcne, propylene, cis-2-butene, tmns-2butene, and isob utene havc been dc rived and have bcen facto red to thc greatest possible cxtent. A potcntial express ion has becn fiLtcd to an assignmcnt of vibrational f requcncies for ethylene and dcuterocthylenc. Some of thc con tants so detcrmined have .bcen used in dcr iving approximatc potcntial cxprcssions for propylcne, cis-2-butcne, trans-2-butenc, and iso butene. WiLh the vibrational frcqucncics calcu lated from thesc potentia l expressions as a gu ide, freq uency assignments have bccn madc for propylcne, cis-2-butcne, trans-2butene, and isob uten e. ' 4 a few trial calculations, it was decided to set Ill12 and Illl3 equal to zero and to find values of IlluJ I1122' I1133' and Illn tha t would most accurately yield the six observed A 1g frequencies of CZH4 and C2D4 No exact so lution is possible even with the most Journal of Research yo general potential expression with ix: constants.