3: Nucleophilic Substitution and Elimination

Question 1

What conditions are required for nucleophilic substitution?

Answer 1

Dilute
Alcoholic
Warm
NaOH or KOH

Question 2

What do nucleophiles attract to?

Answer 2

The carbon that the halogen is attached to.

Question 3

Why do nucleophiles attract to the carbon that the halogen is bonded to?

Answer 3

The carbon is slightly positive due to a difference in electronegativity in the halogen and carbon. Therefore, the negative electron lone pair is attracted to the slightly positive carbon.

Question 4

In nucleophilic substitution, addition of the nucleophile causes what to happen to the halogen?

Answer 4

The bond between the halogen and carbon breaks because only 4 things can be bonded to the carbon at once.

Question 5

In nucleophilic substitution, how is a covalent bond created between the nucleophile and carbon?

Answer 5

The nucleophile shares its lone pair with the carbon.

Question 6

In nucleophilic substitution, what happens to the electrons in the original carbon-halogen bond?

Answer 6

The halogen takes them

Question 7

Name 3 nucleophiles.

Answer 7

NH3, CN, OH

Question 8

Describe the bond formed in a nucleophilic substitution reaction with cyanide.

Answer 8

A triple bond forms between the carbon and nitrogen.

Question 9

Describe the nucleophilic substitution reaction for ammonia.
What is the slight charge on the 1st ammonia?
What is removed from the ammonia? Do any lone pairs remain?

Answer 9

NH3 displaces the halogen.
The nitrogen is slightly positive.
Another NH3 attacks the slightly positive nitrogen, so a hydrogen is broken off, leaving a lone pair.
The hydrogen joins onto the 2nd ammonia forming NH4+.

Question 10

Which carbon halogen bond is the strongest?

Answer 10

C-F

Question 11

How does the bond enthalpy of carbon-halogens change down the group?

Answer 11

Enthalpy decreases.

Question 12

Why do flouroalkanes go through nucleophilic substitutions more slowly than iodoalkanes?

Answer 12

The bond enthalpy in C-F is larger than C-I, so more energy is required to break it.

Question 13

State the conditions for elimination.

Answer 13

Boiling
Reflux
Alcoholic
Catalyst (conc H2SO4)
KOH or NaOH

Question 14

Elimination requires what ion?

Answer 14

-:OH

Question 15

Elimination produces what type of organic product?

Answer 15

Alkene

Question 16

In elimination, what does the -:OH attack?

Answer 16

The H atom on the carbon next to the carbon with the halogen attached.

Question 17

In elimination, once the hydrogen has been attacked, where do electrons move to?
What type of bond does this form?

Answer 17

The carbon-carbon bond.
This now forms a double bond.

Question 18

Why is one of the carbons slightly positive in a haloalkane involved in elimination?

Answer 18

The halogen is electronegative, so draws electron density towards itself.

Question 19

In elimination, why does the halogen break off?

Answer 19

There is not enough room on the carbons now as the double bond has formed, so it breaks off.

Question 20

What do the OH- ions act as in elimination?

Answer 20

Base