7. Ald/Ket II

Question 1

What are alpha C?

Answer 1

any C adjacent to carbonyl C

Question 2

Which is more acidic: ald or ket?

Answer 2

ald b/c methyl of ket are likely to donate e-

Question 3

What are tautomers? Which is a more stable tautomer: keto or enol? What’s an enolate ion?

Answer 3

constitutional isomers that can be easily interconverted; keto
Enolate ion - a keto/enol with either a neg O or carbanion

Question 4

How does keto become enol via acid catalyst?

Answer 4

1) carbonyl O of keto takes H from H3O+
2) structure interconverts to make carbocation
3) water takes methyl H aka alpha H –> enol

Question 5

How does keto become enol via base catalyst?

Answer 5

1) base takes alpha H –> carbonyl C single bonds electroneg O and double bond forms
2) electroneg O takes H from H-base –> enol

Question 6

What else can be tautomerized besides keto/enol? Which of those tautomers are favored?

Answer 6

Enamine-imine. Imine = thermodynamically favored

Question 7

How to do an aldol addn?

Answer 7

1) OH from NaOH grabs alpha H of ald –> resonance structure of carbonyl electroneg O and carboanion
2) carbonanion structure attacks carbonyl C of another ald —> NUCLEOPHILIC ADDN
3) electroneg O from combined carboanion+ald grabs H from water –> aldol

Question 8

How to do base catalyzed aldol condensation?

Answer 8

1) base grabs alpha H from aldol –> resonance structure b/w carboanion and electroneg O (product depends if cis/trans due to steric hindrance) + H2O
2) carboanion makes 2x bond –> -OH becomes leaving group
3) product is an ald/ket with an adjacent alkene + H2O + OH-

Question 9

How does keto genesis occur?

Answer 9

Prolonged starvation, excess acetyl CoA in liver; inc glucagon and catecholamines

Question 10

How do you know if a reagent will [O] -OH to ald/ket or CA intentionally?

Answer 10

If they really only want ald/ket, they will use a reagent specific for [O] to ald/ket. Otherwise, it’ll go straight to CA

Question 11

Order of increasing bpt b/w alcs, alkanes and ald/ket

Answer 11

Alkanes < ald/ket < alcs

Question 12

Are ald more reactive to nucleophilic attacks or ket?

Answer 12

Ald b/c less steric hindrance compared to ket

Question 13

Retro aldol rxn

Answer 13

Reverse ofaldol rxn and/or aldol condensation. You need aq base and heat. Done by breaking bond b/w alpha and beta carbons to make 2 ald or 2 ket or 1 ald + 1 ket

Question 14

Why are alpha H more acidic?

Answer 14

B/c electronegative O from carbonyl like to hog, and for resonance stabilization

Question 15

Kinetic product vs thermodynamic product

Answer 15

Lower Ea needed —> forms faster, get it at low temps, ends with higher deltaG compared to thermodynamic product —> less stable product; IRREVERSIBLE vs high Ea needed —> forms slower, get it at high temps, ends with lower deltaG than kinetic product —> more stable product; REVERSIBLE

Question 16

Trend of good leaving groups on periodic table

Answer 16

Inc down and right

Question 17

Tollens reagent vs Benedict’s reagent

Answer 17

Used to determine ald or ket that can tautomerize into ald; turns silver mirror when ald = present vs there’s aldehyde because it’s copper (ald + 2 Cu2+ –> CA + 2 Cu+ => redox rxn)

Question 18

How to do acid catalyzed aldol condensation?

Answer 18

1) -OH from aldol takes H+ from H3O+
2) H2O conjugate base takes alpha H –> HOH becomes leaving group
3) product is an ald/ket with an adjacent alkene + H2O + H3O+