Dehydration of which one of the following alcohols produces an alkene exhibiting cis-trans isomerism ?

Options

A. Isopropyl alcohol
B. Tertiary butul alcohol
C. n-Butyl alcohol
D. Pentan-3-ol

Answer

D

Explanation

Let us write the products of dehydration of all the alcohols
(a) `underset("Isopropyl alcohol")(CH_(3)-overset(CH_(3))overset(|)(CH)-OH) underset(-H_(2)O)overset("Dehydration "(H^(+)))(rarr) underset("Propene")(CH_(3)-CH=CH_(2))`
(b) `underset("Tet-Butyl alcohol")(CH_(3)-underset(CH_(3))underset(|)overset(CH_(3))overset(|)(C)-OH) underset(-H_(2)O)overset("Dehydration "(H^(+)))(rarr) underset("2-Methylpropene")(CH_(3)-overset(CH_(2))overset(||)(C)-CH_(3))`
(c) `underset("n-Butyl alcohol")(CH_(3)-CH_(2)-CH_(2)-CH_(2)-OH)underset(-H_(2)O)overset("Dehydration "(H^(+)))(rarr) underset("But-1-ene")(CH_(3)-CH_(2)-CH=CH_(2))`
(d) `underset("Neopentyl alcohol")(CH_(3)-underset(CH_(3))underset(|)overset(CH_(3))overset(|)(C)-CH_(2))-OH underset(-H_(2)O)overset("Dehydration "(H^(+)))(rarr)underset("(Major)")(CH_(3)-overset(CH_(3))overset(|)(C)=CHCH_(3))+underset("(Minor)")(CH_(3)-overset(CH_(2))overset(||)(C)-CH_(2)CH_(3))`
(e) `underset("Pentan-3-ol")(CH_(3)-CH_(2)-overset(OH)overset(|)(CH)-CH_(2))-CH_(3) underset(-H_(2)O)overset("Dehydration "(H^(+)))(rarr) underset("Pent-2-ene")(CH_(3)-CH=CH-CH_(2)-CH_(3))`
Of all the alkenes, only pent-2-ene can exhibit geometrical isomerism i.e. it can exist as cis and trans isomers.