Question

Each of the acyl compounds listed below contains a six-membered ring EXCEPT: (A) \(\delta\) -lactam. (B) cyclohexane carboxylic acid. (C) \(\gamma\) -butyrolactone. (D) the anhydride formed from intramolecular ring closure of pentanedioic acid.

Short answer

The answer is C: \( \gamma \)-butyrolactone.

Step-by-step solution

- Understand the Compounds

First, identify and understand the structure of each compound listed in the choices.

- Analyze \( \delta \)-lactam

A \( \delta \)-lactam is a cyclic amide with a six-membered ring.

- Analyze Cyclohexane Carboxylic Acid

Cyclohexane carboxylic acid comprises a cyclohexane ring attached to a carboxylic acid group, making it a six-membered ring.

- Analyze \( \gamma \)-butyrolactone

\( \gamma \)-butyrolactone is a lactone (cyclic ester) with a five-membered ring, not a six-membered ring.

- Analyze Pentanedioic Acid Anhydride

The anhydride formed from intramolecular ring closure of pentanedioic acid results in a five-membered ring.

- Conclusion

Among the options, only \( \gamma \)-butyrolactone does not contain a six-membered ring.

Key concepts

six-membered ring

A six-membered ring refers to a cyclic compound where the ring structure consists of six atoms, usually carbon atoms. These rings are common in organic chemistry because they tend to be more stable than smaller or larger rings. Stability arises from the bond angles and the low strain. Examples include cyclohexane and benzene.

To determine if a compound has a six-membered ring, visualize or draw its structure. Count the number of atoms in the ring. If it's six, then it fits this category.

cyclic compounds

Cyclic compounds are those that have atoms connected in a circular structure. These structures can vary in size and the types of atoms they include.

• Monocyclic compounds: Only one ring in their structure, like cyclohexane or benzene.
• Alicyclic compounds: Non-aromatic compounds with one or more rings. Cyclohexane is an example.
• Aromatic compounds: Contain conjugated systems of double bonds, such as benzene.

Cyclic compounds are crucial in organic chemistry because they often exhibit unique chemical properties.

lactams

Lactams are a class of cyclic amides resulting from the intramolecular formation of an amide bond in amino acid compounds. They are named based on the size of their ring:

• Beta-lactams: 4-membered rings.
• Gamma-lactams: 5-membered rings.
• Delta-lactams: 6-membered rings.

These structures are integral in biology and pharmacology, especially in antibiotics like penicillins, which are beta-lactams.

cyclohexane carboxylic acid

Cyclohexane carboxylic acid is a six-membered ring compound where a carboxyl group (COOH) is attached to a cyclohexane ring. This compound is often represented as C₆H₁₁COOH.

The cyclohexane ring provides stability due to its conformations (chair, boat forms), which minimizes strain in the ring.

A carboxyl group significantly influences the chemical behavior, making it more reactive in carboxylic acid reactions like esterification or amidation.

lactones

Lactones are cyclic esters that result from the intramolecular reaction between a hydroxyl group and a carboxyl group within the same molecule. Lactones are named based on the number of atoms in their ring:

• Gamma-lactones: 5-membered rings.
• Delta-lactones: 6-membered rings.

Lactones are found in nature and various chemical syntheses. They are fragrant compounds often used in perfumes and flavorings. An example is gamma-butyrolactone, which has a five-membered ring and does not fit the criteria for a six-membered ring.