Isomerism: 26 MCQs with answers

Compounds with the same molecular formula but different structures

Isomers are compounds that have the same molecular formula but different arrangements of atoms or spatial orientations, leading to different structures.

Chain isomerism

Butane (n-butane) and isobutane (2-methylpropane) have the same molecular formula C4H10 but differ in the branching of the carbon chain, which is chain isomerism.

cis-2-butene

cis-2-butene is a stereoisomer (geometrical isomer) of trans-2-butene. The others are not stereoisomers relative to a given pair.

False

Isomers have the same molecular formula but different structures, which leads to different physical properties (e.g., boiling points, melting points).

True

Geometrical isomerism (cis-trans isomerism) is a form of stereoisomerism where isomers differ in the spatial arrangement of groups around a double bond or ring.

The existence of compounds with the same molecular formula but different structures or arrangements.

Isomerism refers to the phenomenon where compounds have the same molecular formula but differ in structure or arrangement.

Chain isomerism

Chain isomerism is a type of structural isomerism where the carbon skeleton differs.

Isomers that are mirror images of each other.

Enantiomers are a type of stereoisomer that are non-superimposable mirror images of each other.

2-butanol

2-butanol has a chiral center, allowing it to exhibit optical isomerism.

They differ in the spatial arrangement of groups around a double bond.

Geometric isomers have different spatial arrangements of groups around a double bond, leading to distinct properties.

Isomers that differ in the arrangement of atoms in a chain.

Chain isomers differ in the arrangement of carbon atoms in the carbon chain.

Ethanol and dimethyl ether

Ethanol and dimethyl ether have the same molecular formula but different functional groups, making them functional group isomers.

Position isomerism

1-butanol and 2-butanol differ in the position of the hydroxyl (-OH) functional group, which is characteristic of position isomerism.

They have the same molecular formula but different structures.

Structural isomers have the same molecular formula but differ in their structural arrangement.

Cis-2-butene and trans-2-butene

Cis-2-butene and trans-2-butene are stereoisomers because they differ in the spatial arrangement of groups around a double bond.

Ethanol and dimethyl ether

Ethanol (C2H5OH) and dimethyl ether (CH3OCH3) both have the molecular formula C2H6O but contain different functional groups (alcohol vs ether), so they are functional group isomers.

2-butene

2-butene (CH3-CH=CH-CH3) has a carbon-carbon double bond with different groups attached to each doubly bonded carbon, allowing cis and trans isomers. 1-butene and 2-methylpropene do not show geometrical isomerism because one carbon of the double bond has identical substituents.

Propan-1-ol and propan-2-ol

Propan-1-ol and propan-2-ol have the same molecular formula (C3H8O) and the same functional group (alcohol), but the position of the -OH group differs on the carbon chain, which is position isomerism.

They have the same connectivity of atoms.

Structural (constitutional) isomers have different connectivity of atoms; they do not have the same connectivity. The other statements are true.

1,2-dichloroethene

1,2-dichloroethene (ClCH=CHCl) has different groups (Cl and H) on each doubly bonded carbon, so it can exist as cis and trans isomers. The others have identical substituents on at least one carbon, preventing cis-trans isomerism.

Pentane and 2-methylbutane

Pentane (C5H12) and 2-methylbutane (C5H12) differ in the branching of the carbon chain, so they are chain isomers.

They are non-superimposable mirror images of each other

Enantiomers are stereoisomers that are non-superimposable mirror images of each other, typically arising from a chiral center.

2-chlorobutane

2-chlorobutane has a chiral carbon (C2 attached to Cl, H, CH3, and C2H5), making it optically active. The other compounds do not have a chiral center.

Ionization isomerism

These are coordination compounds that give different ions in solution due to the exchange of the sulfate ion and bromide ion between the coordination sphere and the ionization sphere, which is ionization isomerism.

Acetaldehyde and vinyl alcohol

Acetaldehyde (CH3CHO) and vinyl alcohol (CH2=CHOH) are tautomers that differ in the position of a hydrogen atom and a double bond (keto-enol tautomerism).

It is non-superimposable on its mirror image.

A chiral molecule is one that is not superimposable on its mirror image. It often contains a stereocenter (chiral carbon) and lacks a plane of symmetry.