Aldehydes And Ketones

Question 1

Carbonyl

Answer 1

A double bond between a carbon and an oxygen. Can act as an electrophile or a nucleophile

Question 2

Aldehyde

Answer 2

A terminal carbonyl group.

-ends in al or has the prefix oxo

Question 3

-carbaldehyde

Answer 3

Suffix if aldehyde is attached to a ring

Question 4

Ketones

Answer 4

An internal carbonyl functional group

Suffix one or prefix oxo or keto

Question 5

Describe the physical properties of aldehydes and ketones

Answer 5

They have a dipole but it is less strong than hydrogen bonds seen in alcohols so intermediate boiling point
Can both act as electrophiles because of electron withdrawing effect of oxygen

Question 6

Are aldehydes or ketones more reactive toward nucleophiles

Answer 6

Aldehydes are more reactive because they have less steric hindrance

Question 7

How are aldehydes formed

Answer 7

Partial oxidation of primary alcohol using PCC

Question 8

How are ketones formed

Answer 8

From the oxidation of a secondary alcohol using agents such as sodium or potassium dichromate, chromium trioxide or PCC
-no concern with it being oxidized beyond ketone stage with secondary alcohols

Question 9

Describe the nucleophilic addition reaction

Answer 9

A nucleophile with attack the carbonyl carbon which has a partial positive charge because of the oxygen. The pi bond will break and oxygen will gain a lone pair of e- (that carbonyl will not reform because there is no good leaving group). An H will bind to the o- forming an alcohol

Question 10

Hydration

Answer 10

The nucleophilic oxygen in water attacks the electrophilic carbonyl carbon to form a geminal diol
This reaction will happen slowly unless we add a catalytic base or acid

Question 11

Hemiacetal/hemiketal

Answer 11

One equivalent of alcohol (nucleophile) added to carbonyl. We have retention of the hydroxyl group and the reaction only goes halfway to completion

Question 12

Acetals/ketal

Answer 12

Two equivalents of alcohol are added to the carbonyl and the reaction will proceed to completion to form acetal/ketal via sn1 rxn
Catalyze by anhydrous acid. The hydroxyl group of the hemi is protonated then lost as water
Carbocation is formed and is attacked by alcohol resulting in formation of acetal or ketal
Acetals and ketals are fairly inert and can be used as protecting groups for carbonyls

Question 13

How are acetals/ketals covered back to carbonyls after being used as a protective group?

Answer 13

Aqueous acid and heat

Question 14

Imine

Answer 14

A compound with a nitrogen atom double bonded to a carbon atom

Question 15

How are imines formed?

Answer 15

A nitrogen/nitrogen based functional group acts as a nucleophile and attacks the carbonyl carbon
Water is lost (condensation reaction) and a double bond is formed between the carbon and nitrogen
This is also a nucleophilic substitution because oxygen is gone and nitrogen is added to the carbon

Question 16

What are some of the nitrogen containing groups that can act as nucleophiles to attack the carbonyl carbon ?

Answer 16

Ammonia and its derivatives such as hydroxylamine, hydrazine, semicarbazide,

Question 17

How are enamines formed?

Answer 17

Imine undergoes tautomerization

Question 18

Why/how does HCN (hydrogen cyanide) attack the carbonyl carbon?

Answer 18

HCN is acidic (pka 9.2) so it loses the proton in solution. The nucleophilic cyanide anion can attack the carbonyl carbon
Produces stable compound called cyanohydrins once oxygen has been reprotonated
Gains stability from newly formed c-c bond

Question 19

In the reaction between HCN and a carbonyl what is the nucleophile and what is the electrophile

Answer 19

CN- is the nucleophile and carbonyl carbon is the electrophile

Question 20

What will oxidation an aldehyde to a carboxylic acid?

Answer 20

Any oxidizing agent stronger than PCC such as potassium permanganate, chromium trioxide, silver I oxide , hydrogen peroxide,

Question 21

What is used to reduce ketones and aldehydes to alcohols?

Answer 21

Lithium aluminum hydride (LiAlH4) and sodium borohydride (NaBH4)