Aldehydes and Ketones

Question 1

physical properties

Answer 1

• double bonded oxygen is more electron withdrawing
• dipole moments inc intermolecular attractions
• elevation in bp, but less than that of alcohols because no H-bonding
• act as electrophiles and thus are good targets for nu
• EWG properties explain this, partial positive on carbonyl carbon
• aldehydes more reaction to nu than ketones bc less steric hindrance and fewer e- donating alkyl groups

Question 2

1° alcohol ~~PCC~~>

Answer 2

aldehyde, but any stronger oxidant aldehyde will turn to CA

Question 3

2° alc ~~ (Na or K)2Cr2O7 or CrO3 or PCC~~>

Answer 3

ketone

Question 4

after a nu attack and the electrons are kicked up to the oxygen in rxn w carbonyl…

Answer 4

• no good LG and the nu has covalently bonded to carbon, therefore no carbonyl repair
• tetrahedral intermediate

Question 5

in the presence of water, both aldehydes and ketones form…

Answer 5

geminal diols

o in water is nu

Question 6

basic conditions
aldehyde or ketone react w 1 eq alc

Answer 6

hemiacetal or hemiketal

Question 7

anhydrous acid
aldehyde or ketone react w 2 eq alc

Answer 7

• SN1
• acetal or ketal
• used at protecting groups for carbonyl functionalities
• aqueous acid and heat easily converts them back

Question 8

condensation rxn

Answer 8

• a small molecule is lost during the formation of a bond between two molecules

Question 9

nitrogen and nitrogen-based functional groups act how when reacting with carbonyls

Answer 9

good nu

Question 10

imine formation

Answer 10

• ammonia nu attacks carbonyl carbon, water is lost, imine is formed
• condensation reaction
• nu substitution

Question 11

imines undergo tautomerization to form…

Answer 11

enamines

Question 12

cyanohydrins

Answer 12

• HCN is common nu
• both triple bonds and an electroneg N atom, rendering it relatively acidic
• CN- attacks carbonyl carbon and O is protonated by H+

Question 13

aldehyde reacts with what to become CA?

Answer 13

KMnO4, CrO3, Ag2O, H2O2

Question 14

commons reduction agents

Answer 14

LiAlH4
NaBH4

Question 15

why is it easier to deprotonate a-H (esp in basic conditions)

Answer 15

induction, oxygen pulls some e- density out of these C-H bonds weakening them

acidity of a-H augmented by resonance stabilization of the conjugate base

inc stability of enolate intermediate and EW oxygen helps with this carbanion stabilization

Question 16

why are a-H of ketones less acidic than aldehyde

Answer 16

electron donating properties of the additional alkyl group on ketone

Question 17

a 1,3-dicarbonyl…

Answer 17

• is particularly acidic
• 2 carbonyls delocalize the neg charge
• form enolate carbanions in Michael addition for the nucleophilic carbanion to readily react w electrophiles

Question 18

1,3-dicarbonyl ~base~> ——— ~ketone~>______

Answer 18

• enolate and H—base
• the a of the a,B-unsat bicarbonyl attached to the B-carbon of the ketone

Question 19

which is preferred at lower temp w a strong sterically hindered base? kinetic or thermodynamic enolate.

Answer 19

kinetic

if rxn is reversible then the kinetic product can revert to reactant and form thermodynamic product

Question 20

which is preferred at higher temp w a weak small base? reversible. kinetic or thermodynamic enolate.

Answer 20

thermodynamic

Question 21

enamine vs imine

Answer 21

enamine: double bond between carbons

imine: double bond between carbon and nitrogen

Question 22

aldol condensation

Answer 22

• enolate form more nu than electrophilic carbonyl form
• carbonyl + base = enol
• C2 of enol attacks carbonyl carbon of a carbonyl
• oxygen of the second carbonyl get protonated
• 1,3 aldol formed

Question 23

aldol + strong base and heat

Answer 23

• dehydration
• a,B unsat carbonyl

Question 24

aldol + strong base + water

Answer 24

aldehyde (alcohol side) and ketone
- retro aldol rxn