Question

Which of the following characteristics correctly describe differences between structural (constitutional) isomers? I. these compounds may have different carbon skeletons II. chemical properties are altered due to differences in functional groups III. functional groups may occupy different positions on the carbon skeleton A. I only B. II and III only C. I and III only D. I, II and III

Short answer

D. I, II and III

Step-by-step solution

Identify Structural Isomers

Structural (or constitutional) isomers are compounds with the same molecular formula but different structures.

Analyze Characteristic I

Check if structural isomers can have different carbon skeletons. Yes, they can. Therefore, Characteristic I is correct.

Analyze Characteristic II

Check if chemical properties are altered due to differences in functional groups in structural isomers. Yes, they can be. Therefore, Characteristic II is correct.

Analyze Characteristic III

Check if functional groups may occupy different positions on the carbon skeleton in structural isomers. Yes, they can. Therefore, Characteristic III is correct.

Determine Correct Answer

Since Characteristics I, II, and III are all correct, the answer must include all of them.

Key concepts

carbon skeleton variations

When we talk about carbon skeleton variations, we are referring to the different ways in which the carbon atoms can be arranged in a molecule. Structural isomers, also known as constitutional isomers, are a good example of carbon skeleton variations. These isomers have the same molecular formula but differ in the connectivity of their atoms. This means that the carbon backbone of the molecule can be arranged in different ways, resulting in different structures.
Think of it like LEGO blocks: you have the same pieces, but you can build different structures by connecting the pieces in different ways. For instance, the molecular formulas of n-butane and isobutane are both C4H10, but n-butane has a straight chain of carbon atoms, whereas isobutane has a branched chain.

• This variability in the carbon skeleton contributes to the different physical and chemical properties of the isomers.
• These different structures also mean that isomers may have different melting points, boiling points, and densities.

Understanding carbon skeleton variations is crucial for recognizing how isomers can exist and their unique properties.

functional groups

Functional groups are specific groups of atoms within molecules that have characteristic properties, and they largely determine the chemical reactivity and properties of the molecules they form part of. These can include groups like hydroxyl (-OH), carboxyl (-COOH), amino (-NH2), and many others.
In structural isomers, functional groups can occupy different positions on the carbon skeleton. This is one of the key reasons different structural isomers can have very different chemical properties, even though they have the same molecular formula. Consider ethanol and dimethyl ether, both of which have the molecular formula C2H6O. Ethanol has a hydroxyl group attached to an ethyl chain, making it an alcohol, whereas dimethyl ether has an oxygen atom connecting two methyl groups, making it an ether.

• The position of these functional groups can alter the polarity and the hydrogen bonding capabilities of the molecules, affecting properties like solubility and boiling points.
• This positional variability directly impacts how these molecules interact with other substances, making functional groups a vital concept in organic chemistry.

chemical properties

The chemical properties of a molecule determine how it will react with other substances. These properties can be significantly altered in structural isomers due to variations in carbon skeletons and the positions of functional groups. For example, the presence and position of a functional group can influence the molecule's reactivity, acidity, basicity, and overall behavior in chemical reactions.
Imagine two structural isomers: propylamine and isopropylamine, both of which have the formula C3H9N. Propylamine has an amino group attached to the end of a straight carbon chain, while isopropylamine has an amino group attached to a branched carbon chain. This difference in structure leads to distinct boiling points and solubility.

• The altered positions of functional groups in different isomers can affect how molecules are utilized in biological systems or industrial applications.
• By understanding these chemical properties, chemists can predict and manipulate reactions to synthesize new compounds or optimize existing processes.

Thus, the study of chemical properties in the context of structural isomers is essential for practical applications in chemistry and related fields.