Carbonyls

Question 1

Describe the structure of the carbonyl group ?

Answer 1

• c=o
• trigonal planar = 120
• sp² carbon and oxygen

Question 2

Is a c=c or c=o stronger ?

Answer 2

• c=o is shorter and stronger
• more polar

Question 3

How can carbonyl groups interact at binding sites?

Answer 3

• carbonyl group is a hydrogen bond acceptor

Question 4

What happens during reactions at the carbonyl carbon?

Answer 4

• electron pair moves from C=O bond to the electronegative oxygen atom
• forming a tetrahedral alkoxide ion intermediate
• c goes from sp2 to sp3

Question 5

Which has more steric crowding, aldehydes or ketones?

Answer 5

• ketones
• because attached to 2 alkyl groups whereas aldehydes are only attached to 1

Question 6

What enhances the reactivity of aldehydes, ketones, carboxylic acids, esters, and amides?

Answer 6

• protonation of the carbonyl oxygen to becomes positively charged (O⁺-H)
• makes carbonyl carbon more electrophilic
• more susceptible to nucleophilic attack.

Question 7

How does the carbonyl group react with weak nucleophiles?

Answer 7

• requires activation of carbonyl group
• by protonation of O to make (O⁺-H)
• also called acid catalysis

Question 8

How is nucleophilic addition reversed in basic conditions ?

Answer 8

• base removes H from OH
• forms tetrahedral alkoxide ion
• nucleophile leaves
• carbonyl restored

Question 9

How is nucleophilic addition reversed in acidic conditions?

Answer 9

• protonation of nucleophile
• this then leaves
• H on OH leaves
• carbonyl restored

Question 10

reaction of carboxylic acid with water ?

Answer 10

RCOOH + H2O –> RCOO- +H3O+

Question 11

what kind of acids are carboxylic acids ?

Answer 11

• weak acids

Question 12

Why are carboxylic acids more acidic than alcohols?

Answer 12

• resonance stabilization of the carboxylate anion
• makes stronger acids compared to alcohols.

Question 13

What is the most reactive carboxylic acid derivatives ?

Answer 13

• carboxylic acid (most)
• acyl chloride
• anhydride
• ester
• amide (least)

Question 14

what happens to reactivity as the leaving group becomes more basic ?

Answer 14

• decreased reactivity as more basic
• eg. amide more basic so less reactive

Question 15

What is the effect of resonance on reactivity of derivative ?

Answer 15

• more stable derivative is less reactive eg. amides

Question 16

why is amide less reactive than carboxylic acid ?

Answer 16

• more basic
• more stable resonance structure so less reactive

Question 17

reactions of Acyl chlorides ?

Answer 17

• react with H2O to get COOH
• react with ROH to get ester + HCl
• react with RNH2 to get amide

Question 18

which is more reactive acid anhydride or acyl chloride ?

Answer 18

• acyl chloride

Question 18

Why are aldehydes more reactive than ketones in nucleophilic addition reactions?

Answer 18

• only one large alkyl group = leading to less steric crowding
• so aldehyde carbon more elctrophilic (greater partial positive charge )

Question 18

What happens when aldehydes are oxidized?

Answer 18

• forms carboxylic acid

Question 19

What are anomers + example?

Answer 19

• stereoisomers specific to cyclyic sugars
• α-anomer: (OH) opposite the CH₂OH group, bottom
• β-anomer:(OH) is on the same side as the CH₂OH group, above

Question 20

which anomer is more stable ?

Answer 20

• β-anomer
• more stable - lower in energy

Question 21

What is keto-enol tautomerization?

Answer 21

• interconversion between keto and enol forms, - catalyzed by either acid or base
• involves resonance stabilization.

Question 22

what is an acid anhydride ?

Answer 22

−C(=O)−O−C(=O)−