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Raman Frequencies of Other Double Bonds

Table 7.34 Raman Frequencies of Other Double Bonds... Table 7.34 Raman Frequencies of Other Double Bonds...
The double bond, C=C —The double bond in ethylene and in substitution products of ethylene gives a Raman spectrum in the region 1,600 to 1,680 cm i. In ethylene the value is 1,620 cm, and on the introduction of methyl groups into the molecule the frequency increases, as shown in Table XLIV. In the di-substituted compounds the values for the cis and trans forms are different from each other and different from that in which both methyl groups are attached to the same carbon atom. This distinction may be used as a method of distinguishing between isomers. [Pg.174]

Spontaneous Raman scattering always occurs when the laser excitation frequency is less than the frequency associated with an allowed electronic transition of the molecule. As the probe laser frequency approaches that of an electronic transition in the molecule, certain vibrational modes that couple strongly to the transition increase in intensity (pre-resonance) with respect to other Raman allowed modes of the molecule. When the excitation frequency coincides with the electronic transition frequency (resonance), a dramatic increase in vibrational band intensities is observed. This effect has been observed in many molecules and especially in polymer films, such as polydiacetylene, that consist of extended regions of electron delocalization owing to the presence of conjugated double and triple carbon-carbon bonds in the linear network (40)(41). [Pg.187]

Allenes like other cumulative double bond systems do not show a normal double bond absorption. They have instead, a high frequency antisymmetric absorption which is usually of medium intensity in the infra-red, and a symmetric band at lower frequency which is usually very weak or forbidden in the infra-red and is best seen in the Raman spectra. The antisymmetric band occurs at 1980—1945 cm" in mono-substituted allenes, and at 1930—1955 cm" when di-substituted so that there is no terminal =CH2. Asymmetric di-substitution of the latter type gives this band at 1930— 1915 cm". The symmetric mode appears strongly in the Raman spectra near 1080 cm". ... [Pg.69]

Table 7.7 lists double bond stretching frequencies (some from Raman data) of the 1,2-disubstituted cyclo-enes. Other positions as well as 1 and 2 may be substituted. [Pg.260]


See other pages where Raman Frequencies of Other Double Bonds is mentioned: [Pg.330]    [Pg.16]    [Pg.90]    [Pg.125]    [Pg.70]    [Pg.16]    [Pg.19]    [Pg.34]    [Pg.125]    [Pg.47]    [Pg.36]    [Pg.359]    [Pg.294]    [Pg.1396]    [Pg.1020]    [Pg.307]    [Pg.445]    [Pg.268]    [Pg.37]    [Pg.66]    [Pg.110]    [Pg.395]    [Pg.296]    [Pg.10]    [Pg.317]    [Pg.3]    [Pg.413]    [Pg.535]    [Pg.127]    [Pg.57]   


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