Carbonyls Flashcards
Describe the structure of the carbonyl group ?
- c=o
- trigonal planar = 120
- sp² carbon and oxygen
Is a c=c or c=o stronger ?
- c=o is shorter and stronger
- more polar
How can carbonyl groups interact at binding sites, do they donate or accept H bond ?
- carbonyl group is a hydrogen bond acceptor
What happens during reactions at the carbonyl carbon?
- electron pair moves from C=O bond to the electronegative oxygen atom
- forming a tetrahedral alkoxide ion intermediate
- c goes from sp2 to sp3
Which has more steric crowding, aldehydes or ketones?
- ketones
- because attached to 2 alkyl groups whereas aldehydes are only attached to 1
What enhances the reactivity of aldehydes, ketones, carboxylic acids, esters, and amides?
- protonation of the carbonyl oxygen to becomes positively charged (O⁺-H)
- makes carbonyl carbon more electrophilic
- more susceptible to nucleophilic attack.
How does the carbonyl group react with weak nucleophiles?
- requires activation of carbonyl group
- by protonation of O to make (O⁺-H)
- also called acid catalysis
reaction of carboxylic acid with water ?
- RCOOH + H2O –> RCOO- +H3O+
- transfer a H+ to water
- forms H30+ which is a stronger acid
what kind of acids are carboxylic acids ?
- weak acids
Why are carboxylic acids more acidic than alcohols?
- resonance stabilization of the carboxylate anion (conjugate base)
- makes stronger acids compared to alcohols
- alcohols are neutral in water
What is the order of reactivity for carboxylic acid derivatives ?
- acyl chloride
- anhydride
- ester
- amide (least)
what happens to reactivity as the leaving group becomes more basic ?
- decreased reactivity as more basic
- eg. amide more basic so less reactive
What is the effect of resonance on reactivity of derivative ?
- more stable derivative is less reactive eg. amides
why is amide less reactive than carboxylic acid ?
- more basic
- more stable resonance structure so less reactive
reactions of Acyl chlorides ?
- react with H2O to get COOH
- react with ROH to get ester + HCl
- react with RNH2 to get amide
which is more reactive acid anhydride or acyl chloride ?
- acyl chloride
Why are aldehydes more reactive than ketones in nucleophilic addition reactions?
- only one large alkyl group = leading to less steric crowding
- so aldehyde carbon more elctrophilic (greater partial positive charge )
What happens when aldehydes are oxidized?
- forms carboxylic acid
What are anomers + example?
- 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
which anomer of glucose is more stable ?
- β-anomer
- more stable - lower in energy
What is keto-enol tautomerization?
- interconversion between keto and enol forms, - catalyzed by either acid or base
- involves resonance stabilization.
what is an acid anhydride ?
−C(=O)−O−C(=O)−
Draw the mechanism for the hydrolysis of acyl chlorides
Refer to tutorial sheet
Draw the reaction mechanism for acid-catalysed hydrolysis of esters ?
Refer to tutorial sheet