CHE 3332 – Organic Chemistry 2 – Spring 2021 Week 10 Resource

Hello everyone! Virtual group tutoring for this class will be every Tuesday from 6-7 pm, and you can reserve your spot by making an appointment at www.Baylor.edu/Tutoring. This week, we’ll cover Part 1 of Chapter 20: Ketones & Aldehydes. Keywords: ketone, aldehyde, hydrate, hemiketal, imine, enamine

Naming Aldehydes – Use -al for aldehydes. If aldehyde is the dominant group, it must be in the main chain with numbering starting with the aldehyde.

Butanal 2-propylhexanal Pent-3-en-1-al

• When a formyl group is on the ring, name it as carbaldehyde. Formyl group:

Cyclohexanecarbaldehyde 2-methylcyclopentanecarbaldehyde

Naming Ketones – Use -one for ketones. If ketone is the dominant group, give the carbonyl of the ketone the lowest number. Another way to name ketones is by its alkyl groups.

Butanone Heptan-3-one

(6R)-4-dimethyl-6-ethylnonan-3-one Methyl vinyl ketone How to make aldehydes 1. Oxidation – Only mild oxidizing agents, like PCC, can oxidize a primary alcohol to an aldehyde.

2. Ozonolysis – O3/DMS acts like a surgeon’s blade and neatly cuts the alkene in half, resulting in at least one aldehyde.

3. Hydroboration-oxidation – H2O2 directs the oxidation to go anti-mark, thus putting the carbonyl on the less substituted carbon of the triple bond and making an aldehyde.

How to make ketones 1. Oxidation – An oxidizing agent oxidizes a secondary alcohol to a ketone. Either a mild or strong oxidizing agent can do this.

2. Ozonolysis – O3/DMS acts like a surgeon’s blade and neatly cuts the alkene in half, resulting in at least one ketone.

3. Acid-catalyzed hydration of terminal alkyne – The reaction goes mark, thus putting the carbonyl on the more substituted carbon of the triple bond and making a ketone.

4. Friedel-crafts acylation – An acyl group is added to an aromatic ring to make a ketone.

Nucleophilic Addition to Carbonyls In basic conditions, first the nucleophile attacks the carbonyl and then a proton transfer happens:

In acidic conditions, a proton transfer happens first and then the nucleophile attacks the carbonyl:

Hydrate Formation Either a ketone or an aldehyde can be used. A hydrate is a structure with two hydroxy groups attached to one carbon.

With ketone: With aldehyde:

Acetal & Ketal Formation A ketone results in a ketal and an aldehyde results in an acetal. Two acids can be used in the formation: TSOH & H2SO4. Order of 7 step reaction: proton transfer, nucleophile attacks, proton transfer (hemiketal forms), proton transfer, leaving group leaves, nucleophile attacks, proton transfer (ketal forms). Know the full mechanism!

General reaction:

Structure Review:

Acetal Ketal Hemiketal

Imine Formation A ketone and a primary amine are needed to start the reaction–a primary amine is a nitrogen connected to one alkyl group. Order of 6 step reaction: nucleophile attacks, proton transfer, proton transfer, proton transfer, leaving group leaves, proton transfer (imine forms). Know the full mechanism!

General reaction:

• Other reactions with nitrogen the begin with a ketone:

Enamine Formation A ketone and a secondary amine are needed to start the reaction–a secondary amine is a nitrogen connected to two alkyl groups. Order of 5 step reaction: nucleophile attacks, proton transfer, proton transfer, leaving group leaves, proton transfer (enamine forms). This mechanism is very similar to imine formation!

General reaction:

Quiz: 1. Why are carbonyls (like aldehydes & ketones) so reactive?

2. Name this reaction & complete it:

3. Name this reaction & complete it:

Answers: All questions sourced from the Wiley Organic Chemistry Second Semester textbook.

1. They have a dipole moment due to resonance.

2. Ketal formation

3. Enamine formation