Haloalkanes

Question 1

What is a haloalkane?

Answer 1

A halogen atom has replaced at least one of the hydrogen atoms in an alkane chain

Question 2

How do you name haloalkanes?

Answer 2

Using a prefix of the halogen e.g. fluoro-, chloro-, bromo- or iodo- and then naming the alkane chain e.g. hexane, pentane, ethane

Question 3

What can each haloalkane be classified as? What is this similar to?

Answer 3

• Similar to classifying alcohols
• Primary, one alkyl group bonded to the C of the C-X bond (carbon to halogen bond)
• Secondary, two alkyl groups bonded to the C of the C-X bond
• Tertiary, three alkyl groups bonded to the C of the C-X bond

Question 4

What is the functional group in an haloalkane?

Answer 4

The carbon-halogen bond

Question 5

Why is the C-X bond polar?

Answer 5

Because the halogen atom is more electronegative than the carbon atom

Question 6

Define the term nucleophile

Answer 6

A nucleophile is an electron pair donor

Question 7

What must a nucleophile possess?

Answer 7

A lone pair of electrons

Question 8

Give 4 examples of nucleophiles

Answer 8

• Hydroxide ion OH-
• Ammonia ion NH3
• Water H2O
• Cyanide ion CN-

Question 9

Define what makes a nucleophilic substitution reaction

Answer 9

An electron pair donor replaces a halogen atom

Question 10

What is a hydrolysis reaction?

Answer 10

A chemical reaction involving water or an aqueous solution of a hydroxide ion that causes the breaking of a bond in a molecule. This results in the molecule being split into 2 products

Question 11

What is the reagent needed in the reaction of a haloalkane and hydroxide ions?

Answer 11

Aqueous alkali such as NaOH(aq) or KOH(aq)

Question 12

What conditions are needed in the reaction of a haloalkane and hydroxide ions?

Answer 12

Heat under reflux

Question 13

Describe the nucleophilic substitution mechanism

Answer 13

• The nucleophile (e.g. OH-) is attracted to the electron deficient C atom
• The nucleophile donates its lone pair to form a new covalent bond with the C atom
• This causes the polar C-halogen bond to break by HETEROLYTIC fission. Both electrons in the C-halogen bond move to the more electronegative halogen atom
• The two products are an alcohol and a halogen ion

Question 14

What does the reactivity of a haloalkane depend on?

Answer 14

The strength of the carbon-halogen bond which breaks during the reaction (by heterolytic fission)

Question 15

As you go down group 7 what happens to the reactivity?

Answer 15

It increases