Farhyphen;Infrared Spectra of Ring Compounds. V. Ringhyphen;Puckering Potential Functions of Some Oxygenhyphen;Containing Molecules

摘要

The infrared absorption spectra of gaseous 2,5hyphen;dihydrofuran, 3hyphen;oxetanone, 2hyphen;methylhyphen;4,5hyphen;dihydrofuran, diketene, cyclopentanone, and cyclohexanone have been observed in the range 250ndash;25 cmminus;1. Under high resolution the spectrum of 2,5hyphen;dihydrofuran shows a satellite series ofQbranches in addition to those observed by Shimanouchi and Ueda. The satellites arise from transitions between ringhyphen;puckering energy levels in an excited ringhyphen;twisting state with altered spacing due to higherhyphen;order cross terms in the potential energy. The spectrum of 3hyphen;oxetanone is that of a planar molecule, and the energy levels of the ringhyphen;puckering mode fit a potential function of the formVlpar;xrpar;thinsp;equals;thinsp;ax4thinsp;plus;thinsp;bx2. The absorption of 2hyphen;methylhyphen;4,5hyphen;dihydrofuran is complicated by several lowhyphen;frequency modes, but the spectrum can be fairly well interpreted with a doublehyphen;minimum potential function of the formVlpar;xrpar;thinsp;equals;thinsp;ax4minus;bx2with a barrier height of 98 cmminus;1. Seven sharpQbranches were observed for cyclopentanone, which were fitted to a hindered pseudorotational potential function of the formVthinsp;equals;thinsp;12V2lpar;1minus;cos2phgr;rpar;thinsp;plus;thinsp;12V4lpar;1minus;cos4phgr;rpar;. Although one might also expect diketene and cyclohexanone to have anharmonic outhyphen;ofhyphen;plane ring modes, both compounds gave farhyphen;infrared spectra which appear to be essentially harmonic.