Organic Chemistry

PROBLEM 2

Give the products of the following reactions:

a. e.

b. f.

c. g.

d. h.

Reduction by Addition of an Electron, a Proton,

an Electron, and a Proton

When a compound is reduced using sodium in liquid ammonia, sodium donates an

electron to the compound and ammonia donates a proton. This sequence is then re-

peated, so the overall reaction adds two electrons and two protons to the compound.

Such a reaction is known as a dissolving-metal reduction.

In Section 6.8, you saw the mechanism for the dissolving-metal reduction that con-

verts an alkyne to a trans alkene.

Sodium (or lithium) in liquid ammonia cannot reduce a carbon–carbon double bond.

This makes it a useful reagent for reducing a triple bond in a compound that also con-

tains a double bond.

Reduction by Addition of a Hydride Ion and a Proton

Carbonyl groups are easily reduced by metal hydrides such as sodium borohydride

or lithium aluminum hydride. The actual reducing agent in metal-hydride

reductionsis hydride ion Hydride ion adds to the carbonyl carbon, and the

alkoxide ion that is formed is subsequently protonated. In other words, the carbonyl

group is reduced by adding an followed by an The mechanisms for reduction

by these reagents are discussed in Section 18.5.

−

H 3 O+

C

O−

C

OH

C

O

H

H- H+.

(H-).

(NaBH 4 )

Na or Li

CH 3 C CHCH 2 C CCH (^3) NH 3 (liq)
CC
H CH 3
H
CH 3
CH 3 C CHCH 2
CH 3
Na or Li
CH 3 C CCH (^3) NH 3 (liq)
2-butyne
trans-2-butene
CC
H 3 CH
H CH 3
H 2
NCH (^3) Pd/C
O
CH 3 COCH 3
H 2
Raney Ni
H 2
CH 3 CH 2 CH 2 C CCH 3 O Raney Ni
H 2
Lindlar
catalyst
O
CH 3 CCl
H 2
Raney Ni
H 2
CH 3 CH 2 CH 2 CNPd/C
O
CH 3 CCl
H 2
partially
deactivated
Pd
O
CH 3 CH 2 CH 2 CH 2 CH
H 2
Raney Ni
846 CHAPTER 20 More About Oxidation–Reduction Reactions
BRUI20_841_882r3 01-04-2003 1:11 PM Page 846