Lecture 11_MJD_Pyridine-withnotes

Lecture 11_MJD_Pyridine-withnotes - Chem 302 _ March 5,...

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Chem 302 _ March 5, 2012 (Damha/Sleiman) 1 Otto Maass Building My office (OM413A) masad.damha@mcgill.ca 1 Masad J. Damha Pyridine – Poor reactivity towards electrophiles Pyridine undergoes electrophilic aromatic substitution reactions, but reluctantly! WHY? C3-substitution is preferred Instead, N-substitution is observed
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Chem 302 _ March 5, 2012 (Damha/Sleiman) 2 N-ethyl pyridinium bromide (this is a good brominating agent) 3 N-acetyl pyridinium chloride (a good acylating agent) N-substitution maintains aromaticity of pyridine ring Pyridine – Poor reactivity towards electrophiles bromination of benzene with pyridinium bromide - mechanism:
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Chem 302 _ March 5, 2012 (Damha/Sleiman) 3 The fact that pyridine undergoes N-substitution with E + ’s explains, in part, why it is reluctant to undergo electrophilic aromatic substitution. Nitrogen is more electronegative than carbon. This results in polarization of the pi-system, resulting in decreased electron density on the ring carbons. a)
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This note was uploaded on 03/06/2012 for the course CHEM 302 taught by Professor Sleiman during the Winter '12 term at McGill.

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Lecture 11_MJD_Pyridine-withnotes - Chem 302 _ March 5,...

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