Alkenes group frequencies

C = 0 stretching frequencies are typically lowered by about 20-30 cm 1 from the values given when the carbonyl group is conjugated with an aromatic ring or an alkene group. 

Infrared Analysis. The spectrum of one of the starting materials, 3-sulfolene (Fig. 6.27), is representative of an alkene sulfone. The macro group frequency train for an unconjugated five-membered ring alkene fits the data reasonably... 

Characteristic group frequencies of alkenes are shown in Figure 11. In alkenes, the =CH stretching vibration generally occurs above 3000 cm". In symmetrical irans or symmetrical tetrasubstituted double-bond compounds, the C=C stretching frequency near 1640cm, usually a medium intensity band, is infrared inactive because, in this... 

The structural units which may have group frequencies appearing in the same region as those of the CH3 and CH2 groups were listed in Table 5-X. Alkenes having these groupings would of course be expected to have spectra in which the CH3 and CH2 groups would be difficult to identify. 

The group frequencies associated with alkenes are of two types one is associated with the G=C stretching motion and appears in... 

The CH deformation vibration of alkenes gives distinct bands in the 970-660 cm region. The positions of these bands are determined by the substitution around the double bond. Five types of groupings can occur around a double bond. The five, and the regions in which they show characteristic group frequencies, are... 

Spectra of some alkenes were presented in an earlier section (see Figures 5-7 and 5-8). Additional alkene spectra are presented in Figures 5-14 to 5-19 (Figures 5-15 and 5-16 are located in the pocket on the inside back cover). We will examine these spectra for characteristic group frequencies, considering first the CH stretching vibrations. 

The 970-660 cm region contains a strong group frequency vibration at a position determined by the structure around the double bond. The sensitivity of this group frequency to structure is exemplified by the positions of the band in cis and trans alkenes. In cw-2-butene the band is near 675 cm" while in the trans compound it is near 960 cm The olefinic group frequencies in the 970-660 cm region can be found in the spectra shown in Figures 5.7, 5-8, 5-9, 5-16, 5-17, 5-18, and 5-19. 

In the frequency of their use in 1,3-dipolar cycloadditions to nitrones, alkynes constitute the second group of dipolarophiles after alkenes. They are of particular interest due to the fact that isoxazolines, the products of initial cycloadditions,... 

The absorption frequency of the alkene bond in conjugation with a carbonyl group is lowered by about 30 cm-1 the intensity of absorption is increased. In s-cis structures, the alkene absorption may be as intense as that of the carbonyl group. s-Trans structures absorb more weakly than s-cis structures. 

The absorption of the alkene bond in conjugation with the carbonyl group occurs at a lower frequency than that of an isolated C=C bond the intensity of the conjugated double-bond absorption, when in an s-cis system, is greater than that of an isolated double bond. 

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