AN INFRARED SPECTROSCOPIC COMPARISON OF CIS-CH=CH AND TRANS-CH=CH ANDVINYL CH=CH, GROUP FREQUENCIES OF SOME HEXENES, HEPTENES, AND STEREOSPECIFIC AND NONSTEREOSPECIFIC POLYBUTADIENES

The infrared bands of cis- and trans-CH=CH and vinyl CH=CH2 groups of 1-hexene, trans-2-hexene, trans-3-hexene, 1-heptene, trans- and cis-2- heptene and cis-3-heptene are compared spectroscopically with the band s of the analogous chemical groups in six stereospecific and non-stere ospecific polybutadienes with different cis-, trans- and vinyl microst ructural composition. Special attention is given to the bands associat ed with the vibrations of the in-plane and out-of-plane =CH deformatio n modes. The bands of the cis- and trans-CH=CH groups appear at 1411-1 405, 1310-1300, 1313-1310 and approximate to 1298 cm(-1) for the cis r ho(=CH)a, cis rho(=CH)s, trans rho(=CH)s and trans rho(-CH)a modes res pectively of the olefins and polybutadienes. The trans omega(=CH) mode appears at 975 cm(-1) (with a band-width at half height of 16 cm(-1)) or 967 cm(-1) (with a band-width of 21 cm(-1)) in the spectra of the olefins and the polybutadienes respectively. These values contrast sha rply with those of the cis omega(=CH) mode. The spectra of the olefins show that this mode absorbs infrared radiation at 713 cm(-1) and has a band width at half height of 32 cm(-1) for cis-2-heptene, or at 698 cm(-1) with 34 cm(-1) band-width for cis-3-heptene. The spectra of the polybutadienes show that the maximum absorption of this mode appears between 728 and 739 cm(-1) with band-widths that vary between 70 and 4 0 cm(-1). These observations indicate that the exact position and band -width of the cis omega(=CH) is therefore very dependent on the config uration of the adjacent units, and possibly of units further removed. The bands of the vinyl group appear at 1422-1419, 1308-1295, 995 and 9 13 cm(-1) for the delta(=CH2), rho(=CH), trans omega(=CH)ip and omega( =CH2) modes of the olefins and polybutadienes. The cis omega(=CH)ip mo de splits into two bands at 632 cm(-1) and 554 cm(-1) in the spectra o f the olefins; these bands are associated with the cis and skew rotati onal isomers of the olefins. Unfortunately these bands are not observe d in the spectra of the polybutadienes because of the strong and broad absorption of the cis omega(=CH) mode.