Farhyphen;Infrared Spectra and the Ringhyphen;Puckering Potential Function of Silacyclopenthyphen;3hyphen;ene and Silacyclopenthyphen;3hyphen;enehyphen;1,1hyphen;d2

摘要

A series of a farhyphen;infrared absorption bands have been observed between 35 and 100 cmminus;1in the spectra of silacyclopenthyphen;3hyphen;ene,CH2CHdblbnd;CHCH2SiH2, and silacyclopenthyphen;3hyphen;enehyphen;1,1hyphen;d2. These absorptions result from the transitions between the various energy levels of the ringhyphen;puckering vibration. The frequencies of the bands can be calculated quite accurately using a pure quartic potential,Vthinsp;equals;thinsp;14.34Z4for the hydride andVthinsp;equals;thinsp;13.20Z4for the deuteride whereZis the ringhyphen;puckering coordinate in reduced form. A slightly better fit for each spectrum is obtained by adding a small positive quadratic term to the potential function. The ringhyphen;puckering potential for this molecule shows that the structure of the fivehyphen;membered ring is a planar one and that it has no barrier to inversion like that in cyclopentene. This lack of a potential barrier is attributed to a smaller barrier to internal rotation in the sngbnd;CH2sngbnd;SiH2sngbnd; bond as compared to sngbnd;CH2sngbnd;CH2sngbnd;. Also there is evidence from the isotope shift of the frequencies (which is related to the reduced masses of the 2 isotopic species) that the distance between the silicon atom and the double bond is much smaller than expected. This suggests that a weak bond between the Sidorbitals and thepgr;system is partly responsible for the planarity of the compound.