6 Aldehydes and Ketones I: Electrophilicity and Oxidation-Reduction

Question 1

aldehyde nomenclature

Answer 1

“-al”
“oxo-“

if attached to a ring: “carbaldehyde”

Question 2

ketone nomenclature

Answer 2

“-one”

“oxo-“/”keto-“

Question 3

carbonyl is (EWG/EDG)

Answer 3

EWG

dipole moment draws electron density up to carbonyl oxygen –> results in partial positive charge on carbonyl carbon

Question 4

hydrogen bonding?

Answer 4

NO

Question 5

electrophiles or nucleophiles?

Answer 5

electrophiles (good target for nucleophiles)

Generally, aldehydes are better than ketones.
less steric hindrance
fewer EDG (ex. alkyl groups)

Question 6

forming an aldehyde

Answer 6

primary alcohol –[PCC]–> aldehyde

Question 7

forming a ketone

Answer 7

secondary alcohol –[Na2Cr2O7 or K2Cr2O7]–> ketone

Question 8

nucleophilic addition reactions (general)

Answer 8

1. nucleophile attacks carbonyl carbon
2. electrons from double bond get kicked off onto the carbonyl oxygen
3. add proton source, carbonyl oxygen will protonate

Question 9

hydration

Answer 9

carbonyl hydrated by water –> protonated –> forms geminal diol

Question 10

hemiacetals/hemiketals

Answer 10

1 eq. alcohol + aldehyde/ketone

the oxygen in the alcohol is the nucleophile

Question 11

acetals/ketals

Answer 11

2 eq. alcohol + aldehyde/ketone

hemiacetal/hemiketal is intermediate step

Question 12

enamines

Answer 12

double bond + N-containing group

imine condensation reaction –>[tautomerization]–> enamines

Question 13

imines

Answer 13

nitrogen double-bonded to carbon

ammonia + carbonyl –[-H2O]–> imine

Question 14

cyanohydrins

Answer 14

HCN + carbonyl –> cyanohydrin

HCN pKa ~2 (relatively acidic); dissociates in solution
cyanide (CN-) = nucleophile to attack carbonyl

Question 15

oxidation of aldehydes –> carboxylic acids

Answer 15

any oxidizing agent stronger than PCC:

• KMnO4
• CrO3
• Ag2O
• H2O2

Question 16

reduction by hydride reagents –> alcohols

Answer 16

• LiAlH4

- NaBH4