Question

A halide, `C_(5)H_(11)X`, on treating with alc. KOH gives only pent -2- ene. What is halide ?

Answer 1

Two possible halides which on elimination of HX can form pent-2-ene are:
`underset((I))(CH_(3)CH_(2)CH_(2)CHXCH_(3)) " "," "underset((II))(CH_(3)CH_(2)CHXCH_(2)CH_(3))`
The (II) structure being symmetrical gives only pent-2- ene one on elimination of HX
`CH_(3)CH_(2)CHXCH_(2)CH_(3) overset("alc.KOH")(to) underset("Pent -2-ene")(CH_(3)CH =CHCH_(2)CH_(3))`
Thus the halide is 3-halopentane.