Alkenes infrared spectra, 519 table

The absorption maximum of the cyanine dye can be changed by altering the number of conjugated alkene units linking the cyanine chromophores. This makes the cyanine borate photo-redox pair a so-called tunable photoinitiator, in that compounds which absorb throughout the visible and infrared spectrum can be obtained. Recently, Kabatc et al. [35] described the important features of cyanine borate photo-redox pairs (Table 2). The structures of dyes tested are shown in Figure 5. 

With the exception of iodomethane (CH3I) and neopentyl iodide ((CH3)3CCH2l) all the reactions of 0( P) with the alkyl iodides were found to produce as major product an alkene. An example is shown for 1-iodobutane in Figure 9. Hypoiodous acid (HOI), the probable coproduct in each case, was also identified via its known infrared absorptions at 3620 and 1070 cm (Bames et al., 1992). This compound is, however, very short-lived under the conditions of the experiments and was only visible in the infrared spectrum in the initial stages of the reaction (Figure 10) and could therefore not be quantified. For many of the alkenes calibrated reference spectra were available and the yield of the alkene has been determined. Oxygen atoms also react fairly rapidly with alkenes, therefore, the reaction of O atoms with the alkenes has been taken into consideration when calculating the alkene yields from the O + Rl reactions. The yields and the identity of the alkene for the respective O + RI reactions are listed in Table 1. 

Chemical data for JH III is summarized in Appendix I, Table 1. In the infrared spectrum, the band at 1720 cm- is characteristic of an ester carbonyl group (C=0) and the band at 1650 cnr1 is reflective of the alkene nature of the molecule (C=C) [14,21]. 

There is no mention in Table 4.2 of structures, either on surfaces or in complexes, wherein two or more of the same type of hydrocarbon molecule are attached to the same metal atom or ion. Because of the wide occurrence of carbonyl complexes, where the M—CO bond is similar to that in the alkene complexes, this is somewhat surprising, but in view of their greater size it is likely that steric repulsion would inhibit their formation except perhaps at atoms of low CN. Somewhat unstable complexes of the form " E2M (M=Pt, Pd) are known, that with platinum being the more stable, and a number of complexes denoted as " E2M and " E3M (M=Co, Rh, Ni, Pd, Pt and Cu) have been formed by matrix isolation in a solid Group 0 element at very low temperature, as well as " EM species. The infrared spectrum of " EPd closely resembles that of the adsorbed structure 2, but there are additional bands that, because of the metal-surface selection rule, are not visible for the adsorbed species. Moreover the measurement of UV-visible spectra is possible. This fascinating area of -complex chemistry, which has produced several prophetic insights into catalytic mechanisms, has been sadly neglected for many years it merits renewed attention. 

---