Reactions of carbonyls

Question 1

What can carbonyls be reduced to?

Answer 1

Back to alcohols
Primary alcohol if an aldehyde
Secondary alcohol if a ketone

Question 2

Reducing agent symbol

Answer 2

[H]

Question 3

What is the reducing agent to reduce carbonyl compounds

Answer 3

LiAlH4 in dry ether

Question 4

Conditions for reduction of carbonyls

Answer 4

Dry ether
Room temperature and pressure

Question 5

Nucleophilic addition

Answer 5

Addition of a nucleophile which is an electron pair donor (has electrons) to the molecule

Question 6

What is the nucleophile we add to the carbonyls?

Answer 6

Cyanide ions

Question 7

Reagent for nucleophilic addition of carbonyls

Answer 7

HCN in KCN

Question 8

Why do we use HCN in the presence of KCN?

Answer 8

Increases the concentration of CN- ions present

Question 9

Product of nucleophilic addition of carbonyls

Answer 9

A hydroxy nitrile

Question 10

What is a hydroxynitrile

Answer 10

Where the C=O bond is, the C is now bonded to a hydroxyl group and a cyanide group (C=N)

Question 11

Naming hydroxynitriles

Answer 11

C=N (nitrile) is the main functional group so: working backwards
Longest carbon chain starts at the carbon in the nitrile group
Branching + hydroxy to account for the alcohol group

Question 12

Mechanism for nucleophilic addition: step 1

Answer 12

Lone pair of electrons on C=N- attacks the carbon in the carbonyl group (curly arrow to show this)
C=O bond is polarised and curly arrow from the bond to oxygen to show electrons in bond transferred to oxygen

Question 13

Mechanism for nucleophilic addition:step 2

Answer 13

Intermediate formed: double bond on C=O is now a single bond which uses bonded to C=N but also to O- which has a LONE PAIR OF ELECTRONS

Question 14

Final step of nucleophilic addition

Answer 14

Wash through with acid to proton ate the oxygen with lone pair of electrons to form a hydroxide group

Question 15

Optical activity of hydroxynitrile mixture

Answer 15

Inactive because it’s a racemic mixture so rotational affect of plane polarised light cancelled out

Question 16

Why is the hydroxynitrile mixture optically inactive?

Answer 16

Because the nitrile can attack from above or below the plane: carbonyl has trigonal planar shape
So equal proportions of hydroxynitrile enantiomer

Question 17

Are all hydroxynitrile mixtures optically active?

Answer 17

No because if og carbonyl is a symmetric ketone then there will be no chiral carbon in the final hydroxynitrile product = not optical isomers