Question

2-bromo-3-methylbutane , 2-chlorobutane , 1-chloro-2,2-dimethylpropane. Name the haloalkanes which can be prepared in high yield by monohalogenation of an alkane?

Answer 1

We should get good yields of 2-chlorobutane and 1-chloro-2,2-dimethylpropane.

Explanation:

We have to look at the relative reactivity of each type of `"H"` atom to radical halogenation and calculate the expected yield.

The relative reactivities for radical chlorination are 1°:2°:3° = 1:3.9:5.2 (you may have been given slightly different numbers).

The relative reactivities for radical bromination are 1°:2°:3° = 1:82:1640 (you may have been given slightly different numbers).

2-bromo-3-methyl butane

`("CH"_3)_2"CHCH"_2"CH"_3 → ("CH"_3)_2"CHCHBrCH"_3`
`6 × 1° = 6 ×1 =" "" "color(white)(1)6`
`1×3° = 1 ×1640 = 1640`
`2× 2° = 2× 82 = " "color(white)(1)164`
`3× 1° = 3× 1=" "" "color(white)(1)color(white)(1)3`
`"Total" =" "" "" "" "" "stackrel color (blue)("———")(1813)`

`% 2° = 164/1813 × 100 = 9 %`

We should expect to get a 9 % yield of 2-bromo-3-methylbutane.

2-chlorobutane

`"CH"_3"CH"_2"CH"_2"CH"_3 → "CH"_3"CH"_2"CHClCH"_3`
`6× 1° = 6 × 1 =" "" "6`
`4 × 2° = 4 × 3.9 = color(white)(1)15.6`
`"Total" =" "" "" "" "color(white)(1)stackrelcolor (blue)(———)21.6`
`% 2° = 15.6/21.6 × 100 = 72 % 2°`

We should expect to get a 72 % yield of 2-chlorobutane.

1-chloro-2,2-dimethylpropane

`("CH"_3)_2"CHCH"_3 → ("CH"_3)_2"CHCH"_2"Cl"`

`9 ×1° = 9× 1 =color(white)(1)color(white)(1)9`
`1 × 3° = 1 × 5.2 = 5.2`
`"Total" =" "" "" "color(white)(1)color(white)(1)stackrel(———)14.2`
`% 1° = 9/14.2 × 100 = 63 % 3°`

We should expect to get a 63 % yield of 1-chloro-2,2-dimethylpropane.

Conclusion: We should get good yields of 2-chlorobutane and 1-chloro-2,2-dimethylpropane.