nucleophilic acyl substitutions

Question 1

leaving groups

Answer 1

groups that can be easily kicked off
- stable conjugate bases
- resonance delocalized
- neutral molecules

Question 2

leaving groups for ketones and aldehydes

Answer 2

• nucleophile is generally a LG, so reaction goes back to starting materials

Question 3

leaving groups for carboxylic acid derivates

Answer 3

• derivative group can be the leaving group!

Question 4

saponification

Answer 4

base-catalyzed hydrolysis of esters
- ester group leaves and is replaced by nucleophile, making a carboxylic acid
- carboxylic acid immediately deprotenated by LG to form carboxylate
- if pH is neutralized in a 2nd step (adding acid), the carboxylate will convert back to carboxylic acid

Question 5

hydrolysis of esters

Answer 5

• acid catalysts make carbonyl carbon a better electrophile
• ester becomes a carboxylic acid and an alcohol

Question 6

reduction with metal hydrides

Answer 6

• H is more electronegative than most metals and forms hydrides (H-) that attack carbonyl carbon
• NaBH4 is weak reducing agent
• LiAlH4 is strong reducing agent

Question 7

NaBH4

Answer 7

• works well on aldehydes and ketones–weaker
• works with protic solvents including water
• works at room temp

Question 8

LiAlH4

Answer 8

• reacts violently with water and alcohols, explosive H gas
• used with solvents like diethyl ether
• reactive enough to reduce esters and carboxylic acids, which are less nucleophilic