Chapter 6.6: Reduction
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Describe the mechanism of catalytic reduction
o Step 1: Hydrogen and the alkene are absorbed on the metal surface, and one hydrogen atom is transferred to the alkene forming a new C-H bond. The other carbon remains absorbed on the metal surface. o Step 2: A second C-H bond is formed, and the alkane is desorbed
Define catalytic reduction or catalytic hydrogenation
• Most alkenes are reduced quantitatively by molecular hydrogen H2, in the presence of a transition metal catalyst to give an alkane • Because the conversion of an alkene to an alkane involves reduction by hydrogen in the presence of a catalyst, the process is called catalytic reduction or, alternatively, catalytic hydrogenation
What is the stereochemistry of catalytic reduction?
• Catalytic reduction is stereoselective, with the vast majority proceeding by syn addition of hydrogens to the carbon-carbon double bond
Is the reduction of an alkene to an alkane endothermic or exothermic?
exothermic process
What is the relationship between heats of hydrogenation and degree of substitution of the carbon-carbon double bond?
o Heats of hydrogenation depend on the degree of substitution of the carbon-carbon double bond; the greater the substitution, the lower the heat of hydrogenation