Aldehydes, Ketones, and Carboxylic Acids

Question 1

Cannizzaro’s rxn

Answer 1

• Only seen by aldehydes which do NOT contain alpha hydrogen (formaldehyde, benzladehyde)
• 2 aldehydes + NaOH —> Acid + Alcohol
• cantonese unalpha male was told “na”, drank alcohol and took acid

Question 2

Name tests for distinction bw aldehyde and ketone

Answer 2

1. Tollen’s reagent (aldehyde: silver mirror, ketone: -)
2. Fehling’s soln (aldehyde: red ppt, ketone: -)
3. Schiff’s reagent (aldehyde: red ppt, ketone: no action except acetone (slow))
4. Rxn with NaOH (aldehyde: brown resinous mass (except HCHO), ketone: -)

Question 3

distinction bw formaldehyde and acetaldehyde

Answer 3

Iodoform test
RCHO + NaOH + I2

acetaldehyde: yellow ppt
formaldehyde: no ppt

because iodoform test needs methyl group

Question 4

What is etard rxn

Answer 4

Lab preparation of benzaldehyde from toluene by oxidation with chromyl chloride

Question 5

grw benzaldehyde is more stable than aliphatic aldehydes

Answer 5

• stronger bond bw carbon of the carbonyl bond and benzene ring due to resonance stabilisation
• benzene ring shows +R effect (donates electrons to catbon)
• less negative charge on carbon atom makes it less susceptible to nucleophilic attack and it is mroe stable

Question 6

What is perkin’s rxn

Answer 6

Rxn of benzaldehyde w acetic anhydride to obtain an alpha beta unsaturated product (cinnamic acid) and acetic acid

Question 7

distinction bw aliphatic and aromatic aldehydes

Answer 7

1. Fehling’s soln
2. Benedict’s test
3. Iodoform test