Aldehydes, Ketones and Optical Isomerisms

Question 1

What is the functional group of carboxylic acids?

Answer 1

COOH

Question 2

What is the functional group of Adlehydes?

Answer 2

R-CHO

Question 3

What is the functional group of Ketones?

Answer 3

R-CRO

Question 4

What is the product of reducing Aldehydes, and which mechanism does this use?

Answer 4

Primary alcohol, via nucleophilic addition

Question 5

What is the product of reducing Ketones, and which mechanism does this use?

Answer 5

Secondary alcohols, via nucleophilic addition

Question 6

What is a nucleophile?

Answer 6

An electron paur donor

Question 7

State the reagents and conditions for the reduction of aldehydes and ketones

Answer 7

Reagent- NaBH4
Conditions- aqueous

Question 8

What is the role of :H- ions in reduction of aldehydes and ketones?
What can this be simplified to in a balanced equation?

Answer 8

Nucleophile
[H] in balanced equation

Question 9

What is the product of nucleophilic addition of aldehydes and ketones with KCN and HCl?

Answer 9

Hydroxynitriles

Question 10

What are the reagents for converting aldehydes/ketones into hydroxynitriles via nucleophilic addition?

Answer 10

KCN and dilute HCl

Question 11

In the production of hydroxynitriles via nucleophilic addition, what acts as the nucleophile?

Answer 11

:-CN

Question 12

Why can HCN not be used in the production of hydroxynitriles via nucleophilic addition?

Answer 12

It is a toxic/ corrosive gas that can easily escape into the laboratory.
Whereas KCN is an ionic solid that can be readily dissolved to form a solution

Question 13

What happens when Aldehydes and unsymmetrical ketones undergo nucleophilic addition with KCN and HCl?

Answer 13

A reacemic mixture of two enantiomers (hydroxynitriles) are formed

Question 14

What are optical isomers?

Answer 14

Non-superimposible mirror images, also known as enantiomers

Question 15

What is a racemic mixture?

Answer 15

A mixture of equal amounts of the two enantiomers of a compound

Question 16

How does the shape of an aldehyde or unsymmetrical ketone lead to a racemic mixtire?

Answer 16

The carbonyl carbon has a planar shape, so the nucleophile (CN) can attack the carbon equally from above and below. This gives a racemic mixture that will not rotate plane polarised light

Question 17

What must a compound have to exhibit optical isomerism?

Answer 17

A chiral (asymmetric) carbon that is bonded to four different groups

Question 18

Why do pairs of enantiomers have the same chemical properties?

Answer 18

Because they have the same functional groups

Question 19

How do optical isomers act in polarised light?

Answer 19

Optical isomers rotate plane polarised light by equal amounts in opposite directions

Question 20

How do tou draw optical isomers?

Answer 20

Drawy the structure in a tetrahedral arrangement.
Label the chiral carbon with a *
Draw its mirror image

Question 21

Why do racemic mixtures not rotate plane polarised light?

Answer 21

Because they have an equal ratio of each optical isomer, so rotations cancel out

Question 22

How can a racemic mixtire of enantiomers be formed in a lab?

Answer 22

Via electrophylic addition with but-2-ene and hydrogen bromide

Question 23

During the formation of enantiomers with electrophylic addition, why is it possible that a racemic mixture is formed?

Answer 23

During the intermediate stage, a trigonal planar carbocation is formed
Bromide has equal chances of attacking the carbon from both above and below
Equal amounts of each optical isomer is formed, producing a racemic mixture