"The relative reactivities of the various types of alkane C–H bonds in halogenations can be estimated by factoring out statistical contributions. They are roughly constant under identical conditions and follow the order CH4 < Primary CH < Secondary CH < Tertiary CH ... The reactivity differences between these types of CH bonds are greatest for bromination, making it the most selective radical halogenation process. Chlorination is much less selective, and fluorination shows very little selectivity."