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GATE 2020 CY – Question 27

Organic Chemistry · General Concepts: Structure dependence on properties such as basicity and acidity. Role of aromatic stability on physical properties of organic compounds. · 1 mark · Numerical answer

Among the eight species shown, how many are aromatic?

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Correct answer: 4.0 to 4.0

Explanation

Apply the requirements of continuous cyclic conjugation and a stabilizing 4n+2 π-electron count. The aromatic members are the pyrylium cation (6 π electrons), cyclopropenyl cation (2), the fused phenalenyl-type anion (14), and pyrrole (6, including one nitrogen lone pair). The neutral pyran lacks continuous conjugation; cyclopentadienyl cation, cyclobutadiene and cycloheptatrienyl anion do not provide the required stable 4n+2 system. The count is 4.

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