Heteroatom classification in petroleum: Quinoline is a polycyclic heteroaromatic compound. Identify which heteroatom class it belongs to among sulphur-, nitrogen-, or oxygen-containing species.

Introduction / Context:
Crude oils contain small amounts of heteroatom compounds that influence refining, particularly hydrotreating severity and catalyst life. Quinoline is a classic example encountered in discussions of nitrogen removal and fuel stability. Identifying the heteroatom family clarifies why certain processes target it specifically.

Given Data / Assumptions:

• Compound: quinoline (a fused-ring aromatic).
• Task: choose the correct heteroatom class.
• Context: impact on refining treatments and product quality.

Concept / Approach:
Quinoline consists of a benzene ring fused to a pyridine ring. The pyridine-like ring contains a ring nitrogen atom, making quinoline a basic nitrogen heteroaromatic. Such nitrogenous compounds can poison acid sites on catalysts and require hydrotreating (hydrodenitrogenation) for removal or conversion to ammonia and hydrocarbons.

Step-by-Step Solution:

Verification / Alternative check:
Hydrotreating references list quinoline among basic nitrogen species causing catalyst deactivation; removal is a key benefit of upstream hydrotreaters.

Why Other Options Are Wrong:

Common Pitfalls:
Confusing quinoline (N) with indole (also N but different structure) or with thiophene (S); paying attention to ring heteroatom is critical.

Final Answer:
Nitrogen compound