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why is pyrrole more reactive than furan?

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arghyapikai | Student, Undergraduate | (Level 2) Honors

Posted April 26, 2013 at 7:11 PM via web

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why is pyrrole more reactive than furan?

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llltkl | College Teacher | (Level 3) Valedictorian

Posted April 27, 2013 at 5:13 AM (Answer #1)

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Pyrrole and furan are both five membered heterocyclic aromatic compounds. Nitrogen is the heteroatom in pyrrole whereas it is oxygen in furan. Both are ‘electron deficient aromatic type’ of compound where one lone electron pair from the heteroatom contributes towards the aromatic sextet of electrons.  As expected for aromatics, these compounds tend to react by substitution, taking place by an initial electrophile addition, followed by a proton loss from the "onium" intermediate to regenerate the aromatic ring. The general reactivity order is: pyrrole >> furan. Owing to the lesser electro negativity of nitrogen as compared to oxygen, the nitrogen lone pair is much more available for external electrophiles and as a consequence the nitrogen heterocycles (pyrrole, in this case) are much more reactive than their oxygen analogs.

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