MHT CET · Chemistry · General Organic Chemistry

Which of the following compound is not aromatic?

A 1,3 -cyclobutene
B Pyridine
C Furane
D Thiophene

Verified Solution

Answer & Solution

Correct Answer

(A) 1,3 -cyclobutene

Step-by-step Solution

Detailed explanation

Aromatic compounds satisfy \((4 n+2) \pi\) Huckel rule.
(a) 1,3 -cyclobutene

Number of \(\pi\) electrons \(=4\)
\(\because\) It is not equal to \(4 n+2\)
\(\therefore\) It is not an aromatic compound
(b) Pyridine

Number of \(\pi\) electrons \(=6(=4 n+2)\) (Here lone pair of electrons of N does not evolve in delocalisation)
(c) Furane

Number of \(\pi\) electrons \(=4+2=6(=4 n+2)\)
(d) Thiophene

Number of \(\pi\) electrons \(=6(=4 n+2)\)
Thus, except 1,3 -cyclobutene, all species are aromatic in nature.

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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