Isolated Double Bonds General Aspects

Brown et al.18,19 and Brunet et al.20 studied the rates of hydrogenation of various olefinic compounds over P-1 and P-2 nickel borides and over a nickel catalyst designated Nic, obtained from NaH-f-PeONa-Ni(OAc)2, respectively, in ethanol at 25°C and 1 atm H2 (Table 3.1). Over P-1 Ni, the decrease in the rate of hydrogenation with 2-methyl-l- 

TABLE 3.1 Rates of Hydrogenation of Alkenes over P-1 and P-2 Nickel Boride and Nic Catalysts 

Initial Relative Initial Relative Initial Relative 

Compound Rated Rate Rated Rate Rated Rate 

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The properties of a compound with isolated double bonds, such as 1,4-pentadiene, generally are similar to those of simple alkenes because the double bonds are essentially isolated from one another by the intervening CH2 group. However, with a conjugated alkadiene, such as 1,3-pentadiene, or a cumulated alkadiene, such as 2,3-pentadiene, the properties are sufficiently different from those of simple alkenes (and from each other) to warrant separate discussion. Some aspects of the effects of conjugation already have been mentioned, such as the influence on spectroscopic properties (see Section 9-9B). The emphasis here will be on the effects of conjugation on chemical properties. The reactions of greatest interest are addition reactions, and this chapter will include various types of addition reactions electrophilic, radical, cycloaddition, and polymerization. 

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