21. Bromination of isobutene gives as major product a.n-butyl bromide b.isobutyl bromide c.None of the above d.tert. butyl bromide
The correct option is B Tert-butyl bromide Relative rates of 1 o and 3 o H atoms by bromine are 1:1600. Tert butyl bromide is formed by displacement of 3 o H. It is only one in number. Its relative rate of displacement by bromine is 1600. Formation of 1-bromo-2-methyl propane (Isobutyl bromide) takes place by replacemnt of any of the nine 1 o H atoms. But relative rate of displacement of 1 o H is 1. Total relative rate of displacement of all the nine 1 o H atoms is 9. % of tert butyl bromide = 1600 1609 × 100 = > 90 % % of iso butyl bromide = 9 1609 × 100 = < 10 % So, major product is tert-butyl bromide.
