Question

The chlorination of pentane gives a mixture of three monochlorinated products.

(a) Draw their structures.

(b) Predict the ratios in which these monochlorination products will be formed, remembering that a chlorine atom abstracts a secondary hydrogen about 4.5 times as fast as it abstracts a primary hydrogen.

Short answer

(a)

(b) Ratio of the products are 18.18% : 54.54% : 27.27%.

Step-by-step solution

Primary hydrogen (1o)

A primary hydrogen may be defined as a hydrogen on a carbon attached to only one other carbon atom.

Secondary hydrogen (2o)

A secondary hydrogen may be defined as a hydrogen on a carbon attached to only two other carbon atoms.

Tertiary hydrogen (3o)

A tertiary hydrogen may be defined as a hydrogen on a carbon attached to three other carbon atoms.

Structures of three monochlorinated product and the ratios in which they are formed.

a)

Three monochlorinated products formed are, , and.

(b)

In case of 1- chloropentane,

(6 primary hydrogen) x (reactivity 1.0) =6.0 relative amount of reaction.

In case of 2-chloropentane,

(4 primary hydrogen) x (reactivity 4.5) =18 relative amount of reaction.

In case of 3-chloropentane,

(2 primary hydrogen) x (reactivity 4.5) = 9.0 relative amount of reaction.

Now,

Fraction of 1-chloropentane =6.0/ 6.0+18+9.0 = (6.0/33) x 100% =18.18%.

Fraction of 2-chloropentane =18/ 6.0+18+9.0 = (18/33) x 100% =54.54%.

Fraction of 3-chloropentane =9.0/ 6.0+18+9.0 = (9.0/33) x 100% =27.27%.

Hence, ratio of the products is 18.18% : 54.54% : 27.27%.