Ketones and Aldehydes

Question 1

3 different type of reactions for carbonyl group reactions:

Answer 1

1. If product stable, reaction stops here: Nucleophilic Addition to C=O NaBH4/LiALH4, Grignard reaction
2. If R1 good leaving group: Nucleophilic Substitution to C=O
3. If Nuc has lone pair- loses OH: Nucleophilic Substitution + Replacement of O

Question 2

Ketone:

Answer 2

two alkyl (or aryl) groups bonded to the carbonyl carbon atom

Question 3

Aldehyde:

Answer 3

one alkyl (or aryl) group and one H bonded to the carbonyl carbon atom

Question 4

Positively polarised carbon acts as an ______ (Lewis acid)

Answer 4

electrophile

Question 5

Negatively polarised oxygen acts as an _______ (Lewis base)

Answer 5

nucleophile

Question 6

Synthesis of Ketones and Aldehydes
step 1-4 don’t need to remember
what are steps 5-10?

Answer 6

5. Synthesis of ketones using organolithium reagents with carboxylic acids
6. Synthesis of ketones using organocuprates with acid chlorides
7. Synthesis of ketones from nitriles
8. Aldehyde synthesis by reduction of nitriles
9. Aldehyde synthesis by reduction of acid chlorides
10. Aldehyde synthesis by reduction of esters

Question 6

Synthesis of Ketones and Aldehydes
step 1-4 don’t need to remember
what are steps 5-10?

Answer 6

5. Synthesis of ketones using organolithium reagents with carboxylic acids
6. Synthesis of ketones using organocuprates with acid chlorides
7. Synthesis of ketones from nitriles
8. Aldehyde synthesis by reduction of nitriles
9. Aldehyde synthesis by reduction of acid chlorides
10. Aldehyde synthesis by reduction of esters

Question 7

Most common reaction is nucleophilic addition;

Answer 7

Addition of a nucleophile and a proton (H) across the C=O

Question 8

Reactions of Ketones and Aldehydes - nucleophilic addition

Answer 8

Step 1: A strong nucleophile adds to the carbonyl group to form an alkoxide

Step 2: A weak acid protonates the alkoxide to give the addition product

Question 9

Reverse reaction

Answer 9

Deprotonation, followed by loss of the nucleophile

Question 10

Acid Conditions with weak nucleophile and activated carbonyl

Answer 10

Step 1: Protonation activates the carbonyl group toward nucleophilic attack

Step 2: A weak nucleophile adds to the activated (protonated) carbonyl group

Reverse reaction: Loss of the weak nucleophile, followed by deprotonation

Question 11

Aqueous solution

Answer 11

ketone/aldehyde is in equilibrium with its hydrate (geminal diol)

Question 12

hydration of k and a
IN ACID

Answer 12

weak nucleophile

Question 13

hydration of k and a
IN BASE

Answer 13

strong nucleophile

Question 14

Ketones favours the ____ ______ keto form

Answer 14

non hydrated

Question 15

Aldehydes more likely to form _______ hydrates (Formaldehyde is the most reactive)

Answer 15

stable

Question 16

reactions of k and e

Answer 16

1. Addition of organometallic reagents (Grignard, organolithium- see alcohols)
2. Reduction (see alcohols) - Reduces ketones (2˚alcohols) and aldehydes (1˚ alcoholes)

3/4 not remember

5. Condensations with hydroxylamine and hydrazine

6.Formation of acetals (addition of alcohol)

Question 17

in the formation of imines;

Answer 17

1. acid-catalysed addition of the amine to the carbonyl group
2. acid-catalysed dehydration
   Substituted imine is also called a
   Schiff base
   Condensation Reaction

Question 18

Enols and Enolates

Answer 18

Acidity of Hydrogens bonded to Carbon

Question 19

A hydrogen alpha to a C=O is acidic because :

Answer 19

1) Inductive effect by electron-withdrawal results in C-H bonds being weakened

2) Delocalisation of the resulting negative charge stabilises the enolate anion and favours its formation

Question 20

Tautomerism

Answer 20

isomerisation occurring by the migration of a proton and the movement of a double bond. The isomers that interconvert are called tautomers

Question 21

Reactions under base-conditions occur via the

Answer 21

Enolate

Question 22

Reactions under acidic-conditions occur via the

Answer 22

Enol
Very small amounts of the enol form is present

Question 23

Carbon-Carbon Bond-Forming reaction of

Answer 23

Enolates ( Grignard and Wittig)

Question 24

Aldol Reaction (condensation)

Answer 24

Carbonyl compound used as electrophile and the enolate derived as nucleophile

Question 25

POOR or GOOD Aldol Reaction (condensation)?

Answer 25

very poor:
* Ketones are less reactive than aldehydes as electrophiles* The product from ketone self-condensation is more sterically
compressed\equilibrium favours the starting material