Briefly,but Clearly,explain the Following Observation:
When 2-Methylbutane Reacts with Cl₂/h $v$

Essay

Briefly,but clearly,explain the following observation:
When 2-methylbutane reacts with Cl₂/h $v$ ,the monochlorinated products consist of four constitutional isomers in significant yields.However,when the same alkane is allowed to react with Br₂/ h $v$ ,there is only one major monobromination product.