Question 1

What is the difference between reductive and oxidative ozonolysis?

Accepted Answer

Both begin with ozone treatment of an alkene. Reductive workup with Zn/H2O gives aldehydes and ketones, while oxidative workup with H2O2 converts aldehyde fragments into carboxylic acids and leaves ketone fragments as ketones.

Question 2

Why is a primary alcohol distilled soon after PCC oxidation?

Accepted Answer

PCC oxidizes a primary alcohol to an aldehyde under mild conditions. Because the aldehyde can be oxidized further to a carboxylic acid, it is removed by distillation as soon as possible.

Question 3

What electrophile is used in Friedel-Crafts acylation?

Accepted Answer

The electrophile is the acylium ion, RCO+, generated from an acyl chloride or acid anhydride with anhydrous AlCl3. The aromatic ring attacks the acylium-ion electrophile, and the acyl group is thereby introduced onto the ring to produce an aryl ketone.

Question 4

Why does Friedel-Crafts acylation avoid alkyl-group rearrangement?

Accepted Answer

The reacting electrophile is an acylium ion rather than a carbocation derived from an alkyl group. The acyl group is therefore installed on the aromatic ring without the characteristic alkyl-group rearrangement seen in some Friedel-Crafts alkylations.

Question 5

How can an aldehyde be distinguished from a ketone structurally?

Accepted Answer

An aldehyde has the form R-CHO, so its carbonyl carbon is attached to a hydrogen and a carbon group. A ketone has the form R-CO-R', with the carbonyl carbon attached to two carbon groups.

Preparing Aldehydes & Ketones: Routes to One C=O

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