ALdehydes and Ketones: Enolates

Question 1

Alpha Carbon

Answer 1

adjacent to the carbonyl carbon

Question 2

Alpha Hydrogens

Answer 2

hydrogens connected to the alpha carbon

acidity is augmented by resonance stability of the conjugate base, the extra electrons remaining from H being removed can resonate between: alpha C, carnonyl C, and carbonyl O

this causes increased stability of the enolate intermediate

Question 3

Through _____ , oxygen pulls ______ out of the C-H bonds of alpha C-H bonds weakening them and making it easy to deprotonate the ______ of an aldehyde/ketone.

Answer 3

induction

electron density

carbonyl carbon

Question 4

Alpha hydrogens of ketone tend to be slightly _____ acidic than those of aldehyde due to the electron donating properties of the ________ in a Ketone.

Answer 4

less

alkyl groups

Question 5

Aldehydes are _____ reactive to nucleophiles than ketones because of the ______ from the _____.

The ____ make the ____ a high energy intermediate meaning the reaction is _______ to proceed.

Answer 5

more

steric hinderance

alkyl groups

alkyl groups

ketone

less likely

Question 6

Due to the acidity of the ______, aldehydes exist in solution as a mixture of two isomers: the ____ and ____ form.

Answer 6

alpha hydrogen

keto

enol

Question 7

Enol Form

Answer 7

presence of C-C double bond with an alcohol

occurs from the deprotonation of the alpha carbon by a strong base such as: OH, LDA, KH

Question 8

Tautomers

Answer 8

isomers which differ in placement of a proton and the double bond

aka: keto form vs enol form

Question 9

Equilibrium between the tauromers lies on the ____ side meaning more of the ____ isomer is in solution.

Answer 9

keto

keto

Question 10

Enolization/Tautomerization

Answer 10

process of converting from the kero to the enol tautomer

Question 11

Alpha Racemization

Answer 11

any aldehyde and ketone with a chiral alpha carbon will rapidly become a racemic mixture as the Keto and enol form interconvert

Question 12

Michael Addition

Answer 12

carbanion attacks an alpha, beta unsaturated carbonyl compound (multiple bonds between the alpha and B carbons next to a carbonyl)

Question 13

Given a ketone has two different alkyl groups, each may have a alpha hydrogen meaning _____ enolate forms can exist.

Answer 13

two

Question 14

Kinetic Enolate

Answer 14

rapidly made but less stable

double bond to the less subsituted alpha Carbon

favored in rapid, irreversible, lower temperatures with a strong, sterically hindered base

Question 15

Thermodynamic Enolate

Answer 15

slowly made but more slowly

double bond being formed with the more substituted alpha carbon

favored in reversible, high temperature slow reaction with weaker and smaller base

Question 16

Enamines

Answer 16

tautomers of imines

hydrogen moves to Nitrogen and double bond moves between C-C

Question 17

Imine

Answer 17

compound with a C-N double bond

the nitrogen may or may not be bonded to an alkyl or other substituent

Question 18

Aldol Condensation

Answer 18

aldehyde/ketone acts both as electrophile (keto from) and nucleophile (enol form) and a C-C bond is formed

type od dehydration/condensation reaction

1) enolate is formed when reacting ketone with base
2) due to enolates negative charge on O, it acts as nucleophile and react with the carbonyl of another ketone
3) it attacks the carbonyl carbon and produces an Aldol
4) strong base/high temp creates dehydraton via E1 or E2 to form a double bond between alpha and B carbon

**useful if we only use one type of aldehyde or ketone

if multiple types are used, then there are a mixture of products…but can be avoided if one molecule has no alpha hydrogen (quaternaty alpha carbon)

Question 19

Aldol

Answer 19

compound with both aldehyde and alcohol

Question 20

Retro Aldol Reaction

Answer 20

reverse of aldol condensation by adding aq base and hear

helps break bonds between alpha and B carbons of a carbonyl

only possible if intermediate can be an enol