Nucleophilic addition

Question 1

What is an imine?

Answer 1

A C=N bond - there can be primary and secondary imines based on the number of carbons bonded to the C=N

Question 2

What is the polarity of an imine?

Answer 2

Imines are polar due to difference in electronegativity but they are less polar compared to a carbonyl group

Question 3

What is oxidation?

Answer 3

Gain of C-O bonds
Loss of C-H bonds
Loss of electrons

Question 4

What is a strong oxidising agent example?

Answer 4

H2CrO4 - chromic acid

Question 5

What is a weak oxidising agent example?

Answer 5

PCC

Question 6

What happens when you oxidise a primary alcohol with H2CrO4?

Answer 6

Forms a carboxylic acid

Question 7

What happens when you oxidise a primary alcohol with PCC?

Answer 7

Forms an aldehyde

Question 8

What happens when you oxidise a secondary alcohol with H2CrO4?

Answer 8

Forms a ketone - no further oxidisation

Question 9

What happens when you oxidise a ketone using H2CrO4?

Answer 9

Nothing - ketones are not able to be oxidised

Question 10

What happens when you oxidise a tertiary alcohol with H2CrO4?

Answer 10

Nothing - tertiary alcohols are unable to be oxidised

Question 11

What is the rate determining step of a nucleophilic addition reaction?

Answer 11

The rate determining step of a nucleophilic addition reaction includes both the nucleophile and the carbonyl compound (polar compound)

Question 12

What happens to the rate of nucleophilic addition as the carbonyl compound becomes more substituted?

Answer 12

Substituted groups of a carbonyl compound donate a small amount of negative charge towards the carbon of the C=O bond reducing its partial positive charge and hence slows down the rate of nucleophilic attack

Also, more substitution and the size of the substituted groups means there is more steric interference as the nucleophile tries to attack the partial positive carbon thus also slowing down the rate of reaction

Question 13

What is the reagent for a nucleophilic addition reaction?

Answer 13

Any strong nucleophile (e.g. H-) for the attack on the carbon :
NaBH4 (weaker source of H-)
LiAlH4 (stronger source of H-)
Grignard reagent (RMgX)

Then an acid H30+ for the movement of lone pair of electrons from O- to H+

If the nucleophile and acid are added at the same time they will react together

Question 14

What is grignard addition?

Answer 14

Use of grignard reagents to allow a wider range of R groups to be added to a nucleophile

Question 15

How are grignard reagents made?

Answer 15

By adding Mg, ether to an alkyl halide

RX -> RMgX

Because the magnesium has a much lower electronegativity compared to the carbon the carbon gains a very strong partial negative charge and therefore can be considered a carbanion

Question 16

Can CO2 undergo nucelophilic addition?

Answer 16

Yes, addition of a grignard reagent to CO2 will result in nucleophilic addition on a single C=O bond

Question 17

Can alcohols act as the nucleophile for a nucleophilic addition reaction?

Answer 17

Yes, however as they are weak nucleophiles the electrophile (C=O group) must be activated by addition of H+

Question 18

What is an acetal?

Answer 18

Functional group in which there are two ether groups bonded to the same carbon

Question 19

How do you form an acetal?

Answer 19

Add two molar equivalents of alcohol with acid to a ketone

A hemiacetal forms first and then further nucleophilic substitution occurs to form the acetal

Question 20

How do you form an imine?

Answer 20

Add an amine nucleophile to a ketone to form a hemiaminal C(OH)(NHR)R1R2 then remove a water molecule from this compound via elimination

Question 21

Can imines and nitriles undergo nucleophilic addition?

Answer 21

Yes, they can undergo nucleophilic addition with strong nucleophiles and also weaker oxygen nucleophiles such as water

Question 22

How do you form a ketone from a primary imine?

Answer 22

Add water with acid in a nucleophilic addition reaction to form hemiaminal. Then add water with acid again to form ketone from elimination reaction

Question 23

How do you form a carboxylic acid from a nitrile?

Answer 23

Add acid with water to form an alcohol substituted imine and amide in equilibrium - then add water with acid to substitute NH2 group to form carboxylic acid

Question 24

What effect does nucleophilic addition have on stereochemistry?

Answer 24

If the product is chiral - it will be a racemic mixture as the ketone is a sp2 hybridised molecule

Question 25

Name the reagents for aldehyde/ketone to alcohol

Answer 25

1. NaBH4 or LiAlH4

2. H3O+

Question 26

Name the reagents for aldehyde/ketone to alcohol with R group substitutent

Answer 26

1. RMgX (grignard reagent)

2. H3O+

Question 27

Name the reagents for aldehyde/ketone to an yn-ol

Answer 27

1. RCtriplebondC(-)

2. H3O+

Question 28

Name the reagents for aldehyde/ketone to cyanohydrin

Answer 28

1. NaCN

2. H3O+

Question 29

Name the reagents for aldehyde/ketone to hemiacetal

Answer 29

ROH / H+

Question 30

Name the reagents for hemiacetal to acetal

Answer 30

ROH / H+ (substitution)

Question 31

Name the reagents for aldehyde/ketone to imine

Answer 31

NH2R (no need for acid as amine strong enough nucleophile)

Addition will occur first forming a hemiaminal then elimination to form imine

Question 32

Name the regaents for imine to amine

Answer 32

1. LiAlH4

2. H3O+

Question 33

How do you form a grignard reagent?

Answer 33

React an alkyl halide with Mg to form R-MgX