In gasoline stability, which hydrocarbon family tends to show the highest gum-forming tendency during storage: paraffins, naphthenes, aromatics, or diolefins?
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AParaffins
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BDiolefins
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CAromatics
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DNaphthenes
Answer
Correct Answer: Diolefins
Explanation
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:
1) Rank families by unsaturation and radical stability.2) Recognize dienes (diolefins) as most reactive for gum formation.3) Select “Diolefins.”Verification / Alternative check:ASTM gum tests and textbook trends consistently show highest gum precursors in olefinic—especially diene—fractions.Why Other Options Are Wrong:
Paraffins: saturated; poor gum formers.Aromatics: relatively stable ring; lower gum tendency than dienes.Naphthenes: saturated cyclics; low gum tendency.Common Pitfalls:Assuming high octane (aromatics) implies instability; octane and oxidative stability are distinct properties.
Final Answer:Diolefins