Chemical representation of naphthenic acids: select the most appropriate general formula for cycloaliphatic (naphthenic) monocarboxylic acids commonly found in certain crude oils.

Introduction / Context:
Naphthenic acids are naturally occurring cycloaliphatic carboxylic acids in some crude oils that can cause corrosion and refining challenges. Understanding their general formula helps distinguish them from straight-chain fatty acids and from aromatic acids.

Given Data / Assumptions:

• Naphthenes are saturated cyclic hydrocarbons.
• We consider monocarboxylic acid derivatives of these rings.
• Formulae are given in generalized C/H/O forms with O2 indicating a single -COOH group.

Concept / Approach:
For aliphatic (acyclic) monocarboxylic acids, a common general formula is CnH2nO2, reflecting one ring-equivalent compared with alkanes (CnH2n+2). Cycloaliphatic acids (naphthenic acids) incorporate the ring deficiency of the cycloalkane core and the carboxyl group, often represented in petroleum texts by the generalized form CnH2n-2O2. This captures the hydrogen deficiency from ring formation relative to the acyclic series.

Step-by-Step Solution:

Verification / Alternative check:
Petroleum chemistry references frequently use the CnH2n-2O2 shorthand for naphthenic acids, distinguishing them from normal fatty acids (CnH2nO2) and from alkanes (CnH2n+2).

Why Other Options Are Wrong:

Common Pitfalls:
Confusing straight-chain fatty acids with naphthenic acids; ring formation changes hydrogen count relative to acyclic analogs.

Final Answer:
CnH2n-2O2