Chapter 6.6: Reduction

Question 1

Describe the mechanism of catalytic reduction

Answer 1

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

Question 2

Define catalytic reduction or catalytic hydrogenation

Answer 2

• 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

Question 3

What is the stereochemistry of catalytic reduction?

Answer 3

• Catalytic reduction is stereoselective, with the vast majority proceeding by syn addition of hydrogens to the carbon-carbon double bond

Question 4

Is the reduction of an alkene to an alkane endothermic or exothermic?

Answer 4

exothermic process

Question 5

What is the relationship between heats of hydrogenation and degree of substitution of the carbon-carbon double bond?

Answer 5

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