In gasoline stability, which hydrocarbon family tends to show the highest gum-forming tendency during storage: paraffins, naphthenes, aromatics, or diolefins?

Introduction:
Gum formation in gasoline arises from oxidative polymerization of reactive unsaturates. Identifying the hydrocarbon class most prone to forming gums is essential for storage stability and additive selection.

Given Data / Assumptions:

• Compare gum tendency among paraffins, naphthenes, aromatics, and diolefins.
• Ambient storage with oxygen exposure is implied.

Concept / Approach:
Reactivity increases with unsaturation: diolefins (dienes) > mono-olefins > aromatics ≈ naphthenes ≈ paraffins (least). Dienes readily oxidize and polymerize, generating gums.

Step-by-Step Solution:

Verification / Alternative check:
ASTM gum tests and textbook trends consistently show highest gum precursors in olefinic—especially diene—fractions.

Why Other Options Are Wrong:

Common Pitfalls:
Assuming high octane (aromatics) implies instability; octane and oxidative stability are distinct properties.

Final Answer:
Diolefins