Of cumulated double bonds

Table 7.20 Absorption Frequencies of Single Bonds to Hydrogen Table 7.21 Absorption Frequencies of Triple Bonds Table 7.22 Absorption Frequencies of Cumulated Double Bonds Table 7.23 Absorption Frequencies of Carbonyl Bands...

Table 7.32 Raman Frequencies of Cumulated Double Bonds...

When three, five, or any odd number of cumulative double bonds exist, orbital overlap causes the four groups to occupy one plane and cis-trans isomerism is observed. When four, six, or any even number of cumulative double bonds exist, the situation is analogous to that in the allenes and optical activity is possible. Compound 20 has been resolved. ... 

Several curious molecules with cumulated C=C bonds and a carbonyl group at the end have received attention. Problems were the separation of unstable compounds and the measuring technique, and also the direction of the dipole moments and sometimes even the geometry the exact linearity can be doubted in some cases. In the series of compounds 63 with an increasing number of cumulated double bonds, the dipole moments (in the gas phase) change in an irregular way156 the compound with n = 2 is not linear. 

Several kinds of cumulative double bonds containing heavier atoms such as Si=C=C, Si=C=C=C, N=C=Si (precisely, RN=C - SiR2), Si=C=P, and so on, and then-heavier congeners have been synthesized and reported as stable or marginally stable compounds. Here, the main topic in this section is limited to the stable and isolable examples of allene derivatives containing heavier group 14... 

The hydrogenation of cumulative double bonds (allenes) takes place at a rate comparable to that of the corresponding acetylene but no isomerization to the acetylene is observed during the reaction. "5 Selective hydrogenation to the alkene occurs since the allene readily displaces the product olefin from the catalyst before the hydrogenation can take place. Selectivities for monoalkene formation of greater than 95% were commonly obtained in the hydrogenation of various substituted allenes." This reaction selectivity is probably facilitated by the fact that the n electron clouds of the two double bonds are perpendicular to... 

In the context of the ethynyl sulfones 6.30 Padwa s cycloadditions of phenylsulfonyl-substituted propa-1,2-dienes like 6.31 with diazomethane should be mentioned briefly (Padwa et al., 1993a, with many references on allenes used as dienophiles). The example in (6-22) demonstrates the regiospecificity of the cycloaddition to the more reactive electron-deficient 71 bond. The ready reactivity of cumulated double bonds is based on the relief of strain when the 1,2-propadiene... 

Complete reduction of alkynes involves liberation of about as much heat as compounds with the same number of cumulative double bonds (compare propyne with 1,2-propadiene Table 3.4). 

An intact system of cumulated double bonds is a foremost requirement for antiretroviral activity of adenallene (He) and cytallene (Hd). This is confirmed by the fact that... 

The following are representations of a molecule with a pair of cumulated double bonds. 

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