Aldehyde and Ketones

Question 1

Draw an aldehyde

Answer 1

R - C - H
Double bond O out of C

Question 2

Draw a ketone

Answer 2

R - C - R
Double bond O out of C

Question 3

What is the oxidation step of aldehydes and products it forms

Answer 3

Aldehyde + [O] -> C=O and OH
Forming carboxylic acid

Question 4

What is the oxidation step of ketones and its products

Answer 4

Ketones can’t be oxidised

Question 5

Why can’t ketones oxidise

Answer 5

do not have hydrogen atom attached to their carbonyl, they are resistant to oxidation. Only very strong oxidizing agents such as potassium manganate(VII) solution oxidize ketones.

Question 6

Reduction of aldehydes steps and products

Answer 6

aldehyde + 2[H] -> primary alcohol R-C-H with OH attached to C

Question 7

Reduction of ketones steps and products

Answer 7

Ketone + 2[H] -> R-C-R and OH on C
Secondary alcohol

Question 8

What is the mechanism name reaction for aldehydes and ketones

Answer 8

Nucleophilic addition

Question 9

Draw the mechanism for Nucleophilic addition of aldehydes and ketones

Answer 9

.

Question 10

Solution X reacts with liquid ketones to form a crystalline solid.
This reaction can be used to identify a ketone if the crystalline solid is separated, purified by recrystallisation, and the melting point determined.
Describe how the crystalline solid is separated and purified.

Answer 10

filter
dissolve in minimum vol
of hot solvent
cool AND filter (under reduced pressure)
Wash with cold solvent/water, and dry (with method)

Question 11

Propanone reacts with the weak acid HCN to form a hydroxynitrile.
This hydroxynitrile is made by reaction of propanone with KCN followed by dilute acid, instead of with HCN
State the hazard associated with the use of KCN
Suggest a reason, other than safety, why KCN is used instead of HCN.

Answer 11

Toxic/poisonous gases produced
KCN is used because KCN dissociated more than HCN

Question 12

Outline the mechanism for the reaction of propanone with KCN followed by dilute acid.

Answer 12

Look at camera roll ss

Question 13

Aqueous NaBH4 reduces aldehydes but does not reduce alkenes.
(a) Show the first step of the mechanism of the reaction between NaBH4 and 2-methylbutanal.
You should include two curly arrows.
Explain why NaBH4 reduces 2-methylbutanal but has no reaction with 2-methylbut-1-ene.
First step of mechanism

Answer 13

nucleophile is attracted to δ+ C
electron rich C=C
nucleophile is repelled by C=C