Which one of the following compounds will be most readily dehydrated?
1
2
3
4
The ease of dehydration of the given compounds can be explained on the basis of the stability of the carbocation formed. In case of options (a), (b) and (d), a secondary carbocation is formed but the presence of an electron withdrawing group adjacent to the positively charged carbon, intensifies the charge and hence destabilises the species.
However, in case of option (c), a secondary carbocation is formed, but the electron withdrawing group
is present farther away, as a result, the effect of this group is diminished and hence the carbocation is relatively more stable.