Identify which of the following is not a sulphur-containing compound commonly found in crude oil and petroleum fractions.

Introduction:
Crude oil contains a mix of heteroatomic species. Distinguishing sulfur- from nitrogen-containing classes is crucial for selecting hydrotreating conditions and understanding catalyst deactivation patterns.

Given Data / Assumptions:

• We compare typical sulfur species (thiols/mercaptans, sulfides, thiophenes, sulphones) to a nitrogen heterocycle (pyrrole).
• Goal: pick the one that is not sulfur-bearing.

Concept / Approach:
Petroleum sulfur occurs as mercaptans (R–SH), sulfides (R–S–R), disulfides (R–S–S–R), thiophenic rings (aromatic sulfur), and oxidized forms such as sulphones. Pyrroles, by contrast, are five-membered nitrogen heterocycles (–NH– in the ring) and belong to nitrogen compound families, not sulfur.

Step-by-Step Solution:
1) List sulfur families present in crude: mercaptans, sulfides/disulfides, thiophenes, sulphones.2) Recognize pyrrole as a nitrogen heterocycle.3) Select pyrroles as the non-sulfur compound among the options.

Verification / Alternative check:
Hydrotreating practice differentiates hydrodesulfurization (HDS) from hydrodenitrogenation (HDN); pyrrolic species are targeted under HDN pathways, confirming they are nitrogen, not sulfur.

Why Other Options Are Wrong:
Thiophenes, mercaptans, sulphones, sulfides/disulfides all contain sulfur and are routinely cited in crude assays.

Common Pitfalls:
Spelling variants (pyroles/pyrroles) can distract; chemically, they are nitrogen compounds.

Final Answer:
Pyroles (pyrroles)