The formation Alkenes by the dehydration of alcohols (using concentrated H2SO4) the hydrogen atom will be removed (to remove as water) from the adjacent carbon atom linked to the less number of hydrogen atoms.

Example: In the dehydration of Butane – 2Ol

2Butane is formed

CH3-CH=CH-CH3+H2Oàconcentrated H2SO4àCh3-CH2-CH-CH3

But2-ene