OZ.8

Question 1

What is produced in the homolytic fission of halogenoalkanes?

Answer 1

Radicals of halogens.

Question 2

What is a condition required for homolytic fission of halogenoalkanes?

Answer 2

UV radiation.

Question 3

What is produced in the heterolytic fission of halogenoalkanes?

Answer 3

Halide ion and a carbocation.

Question 4

What is a substitution reaction?

Answer 4

A reaction in which one atom or a group in a molecule is replaced by another atom or group.

Question 5

What is a nucleophile?

Answer 5

A molecule or negatively charged ion that has a lone pair of electrons and can donate the electrons to form a covalent bond.

Question 6

What is the reaction called where a nucleophile replaces another group on a molecule?

Answer 6

Nucleophilic substitution.

Question 7

In nucleophilic substitution, what is the replaced group called?

Answer 7

The leaving group.

Question 8

What are some examples of nucleophiles?

Answer 8

• H2O water
• OH- hydroxide ion
• NH3 ammonia
• CN- cyanide ion
• C2H5O- ethoxide ion
• CH3COO- ethanoate ion

Question 9

With Nuc- as a general symbol for nucleophile and X as a symbol for a halogen atom, what is the equation for a general nucleophilic substitution of a halogenoalkane?

Answer 9

R-X + Nuc- → R-Nuc + X-

Question 10

What is the general equation for a nucleophilic substitution with water, also known as hydrolysis reaction?

Answer 10

R-X + H2O → R-OH + H+ + X-

Question 11

What is the general equation for nucleophilic substitution with ammonia?

Answer 11

R-X + NH3 → R-NH2 + H+ + X-

Question 12

What is the product from nucleophilic substitution with ammonia with general formula R-NH2 called?

Answer 12

Amine.

Question 13

How can halogenoalkanes be made using nucleophilic substitution?

Answer 13

Using the reverse of the hydrolysis reaction, the halide ion acts as a nucleophile and attacks the alcohol.

Question 14

What condition is required for making halogenoalkanes from alcohols?

Answer 14

Acidic condition.

Question 15

What is the trend in bond polarity for C-halogen bonds?

Answer 15

Bond polarity decreases.

Question 16

What is the trend in bond strength/enthalpy for C-halogen bonds?

Answer 16

Bond strength decreases. Bond enthalpies get less endothermic, which means less energy is required to break the bonds.

Question 17

Regarding bond polarity, which C-halogen bond would you expect to be most easily hydrolyzed?

Answer 17

C-F because it is the most polar.

Question 18

Regarding bond enthalpy, which C-halogen bond would you expect to be most easily hydrolyzed?

Answer 18

C-I because it is the weakest.

Question 19

In reality, which factor, bond polarity or bond enthalpy is more important in determining the difficulty of hydrolyzing a C-halogen bond?

Answer 19

Bond enthalpy is more important. In reality C-I bonds are most easily hydrolyzed.

Question 20

What is the trend in reactivity of halogen compounds?

Answer 20

They get more reactive. Fluoro compounds are very unreactive because of its high bond enthalpy.