Q4. Write the four alcohols with the formula C4H10O and say how they are related.
Butan-1-ol, CH3CH2CH2CH2OH; butan-2-ol, CH3CH(OH)CH2CH3; 2-methylpropan-1-ol, (CH3)2CHCH2OH; 2-methylpropan-2-ol, (CH3)3COH. Butan-1-ol and butan-2-ol are position isomers (same chain); butan-1-ol and 2-methylpropan-1-ol are chain isomers (different skeletons). With its three ethers (1-methoxypropane, 2-methoxypropane, ethoxyethane), C4H10O has seven structural isomers, or eight counting butan-2-ol’s two mirror-image forms.
Q5. Methoxybutane, CH3OC4H9, and ethoxypropane, C2H5OC3H7, are both C5H12O. What kind of isomers are they?
Metamers: both are ethers, but the alkyl groups on the two sides of the oxygen differ (methyl and butyl against ethyl and propyl).
Q6. Which of butan-2-ol and propan-2-ol can show optical isomerism? Explain.
Butan-2-ol: its second carbon carries four different groups (H, OH, CH3 and C2H5), so the molecule is not superimposable on its mirror image. Propan-2-ol: its middle carbon carries two identical CH3 groups, so it has no optical isomers.
Q7. Write the isomers of C2H4Cl2 and name the type of isomerism.
1,1-Dichloroethane, CH3CHCl2, and 1,2-dichloroethane, ClCH2CH2Cl: position isomers.
Q8. Does 1,2-dichloroethene, ClCH=CHCl, show geometrical isomerism?
Yes. Each carbon of the C=C carries two different groups, H and Cl, so there are cis (both Cl on the same side) and trans (opposite sides) forms.