Ochem 2: Reduction and Oxidation

Chapter 12 - Reactions

Alcohol acidity ranking

1* = most acidic

2* = acidic

3* = least acidic

• all carbon stabilized

When pka is lower…

H is more acidic = CB is favored

What is reduction?

• Involves a decrease in oxidation

• makes less bonds

What is oxidation?

• Involves an increase in oxidation

• makes more bonds

What does reduction convert?

A carbonyl to an alcohol

What does oxidation convert?

An alcohol to a carbonyl

What is the WEAK reagent for reduction?

Sodium borohydride - NaBH₄

• reacts with ONLY aldehydes + ketones

What is the STRONG reagent for reduction?

Lithium aluminum hydride - LiAlH₄ (LAH)

• reacts with ALL carbonyls

  • Carboxylic Acid + Esters must use xs LiAlH₄

What is formed in an ester reduction mechanism?

tetrahedral intermediate

• breaks polar covalent bond C-OR’

Reduction for Aldehyde

• product has 1* alcohol

Reduction for Ketones

• product has 2* alcohol

Reduction for Carboxylic Acids

• product has 2* alcohol

Reduction for Ester

• product has 1* alcohol

The weak oxidizing reagent

PPC

Strong oxidizing reagents

• Chromic acid: H₂CrO₄

• CrO₃, H⁺, acetone

• 1) Na₂Cr₂O₇ 2) H₂SO₄, H₂O