Write the structures of all isomeric alcohols of molecular formula `C_4H_10O`. How many pi-diastereoisomers are possible in each case after dehydration ?

Explanation

Possible isomeric alcohols are :

Acid catalysed dehydration of alcohols sometimes occurs with isomerisation. Compounds with the same molecular formula and identical constitution but differing only in spatial arrangement give rise to stereoisomers and stereoisomers that do not bear any mirror image object relationship are known as diasteroisomers.
Butan-1-ol on dehydration gives but-1-ene and but-2-ene (major product).
`CH_3CH_2CH_2 CH_2 OH underset(-H_2O)overset(H^(+))to underset("But-1-ene")(CH_3-CH_2 CH) = CH_2`
(It has no diastereomers)

Butan-2-ol also gives but-1-ene and but-2-ene which exists in the form of two diastereomers.

2-Methylpropan-1-ol on dehydration gives a mixture of three alkenes.

Only the major product constitutes a pair of diastereomers. 2-Methylpropan-2-ol on dehydration gives methylpropene which has no diastereomer.