What type of isomerism involves compounds with the same molecular formula but different arrangements of atoms?

• A. Cis-trans isomerism
• B. Geometric isomerism
• C. Structural isomerism
• D. Stereoisomerism

Answer: (C)

The concept of structural isomerism refers to compounds that share the same molecular formula but differ in the connectivity or arrangement of their atoms. This means the atoms are bonded together in different ways, leading to variations in the compound's structure and therefore its chemical properties. For instance, structural isomers can include variations like straight-chain and branched forms of a compound, or different functional groups attached to the same carbon skeleton.

In contrast, the other forms of isomerism provided as choices are subsets of isomerism that specifically involve different spatial configurations rather than different attachments of atoms. Cis-trans isomerism and geometric isomerism typically refer to cases where there is restricted rotation around a bond, usually in the context of alkenes, while stereoisomerism encompasses all types of isomerism where the connectivity of atoms remains the same, but their spatial arrangement does not. Hence, while these may be significant types of isomers, they do not capture the broader concept of structural isomerism, which is particularly focused on variations in the atoms' bonding patterns.