Halogenoalkanes (Chapter 13)

Question 1

Define Haloalkanes

Answer 1

Alkanes which have one or more hydrogen atoms that have been replaced by halogen atoms.

Question 2

What is the generic formula for haloalkanes

Answer 2

R-X

R = Carbon chain
X = Halogen

Question 3

Why are covalent bonds polar?

Answer 3

The electrons are not equally shared because one atom spends more time with the electrons than the other atom.

Question 4

Where do the reactions take place on a haloalkane?

Answer 4

On the polar bond

Question 5

What is the difference between symmetrical and asymmetrical CX4 molecules?

Answer 5

Asymmetrical ARE polar

Symmetrical ARE NOT polar

Question 6

How do haloalkanes form?

Answer 6

Free radical substitution

Question 7

What are the steps of free radical substitution?

Answer 7

Initiation, Propagation and Termination

Question 8

What happens in initiation?

Answer 8

UV light is required which forms two free radicals

Question 9

What happens in propagation?

Answer 9

2 reactions which form chain reaction

Question 10

What happens in termination?

Answer 10

Two free radicals join to form one molecule

Question 11

How are unpaired electrons shown?

Answer 11

Using a dot •

Question 12

What is the link between bond enthalpy and polarity?

Answer 12

As bond enthalpy decreases, polarity also decreases

Question 13

What does a double-headed arrow show?

Answer 13

The movement of two electrons

Question 14

What does a single-headed arrow show?

Answer 14

The movement of one electron

Question 15

What are the products of propagation?

Answer 15

Multiple substitutions (di-, tri-, tetra etc haloalkanes)

Question 16

What are the products of termination?

Answer 16

Longer chains which also react during a subsequent initiation step .

This is because X• can replace any hydrogen atoms so more isomers form.

Question 17

How are the products of FRS separated?

Answer 17

Fractional distillation

Question 18

What reactions do haloalkanes undergo?

Answer 18

Nucleophilic and elimination reactions

Question 19

What is a nucleophile?

Answer 19

An atom/molecule with a lone pair of electrons (so has a negative charge) so is attracted to a positive charge.

Question 20

Describe a nucleophilic substitution reaction

Answer 20

A nucelophile substitutes the halogen atom on the haloalkane molecule.

Different nucleophiles form diferent organic products (which undergo additional reaction).

Question 21

What are the conditions for nucleophilic substitution?

Answer 21

50:50 mix of ethanol and water

Warm gently

Question 22

How is a nitrile (RCN) formed?

Answer 22

Reacting a cyanide (:CN) with a haloalkane (RX)

Question 23

How is an amine (RNH2) formed?

Answer 23

Reacting ammonia (:NH3) and a haloalkane (RX) in a 2:1 ratio.

The Ammonia replacesa H atom on the RX

Question 24

How is an alchol (ROH) formed?

Answer 24

Reacting a hydroxide (:OH) with a haloalkane (ROH)

Question 25

What are the conditions for an elimination reaction?

Answer 25

100% ethanoic solution

Question 26

Describe an elimination reaction

Answer 26

The hydroxide acts as a base and removes a H atom from the C-H adjacent to the C-X of the haloalkane.