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Topic: Nitrogen lone-pair in pyridine and pyrrole  (Read 6223 times)

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Offline joanne

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Nitrogen lone-pair in pyridine and pyrrole
« on: October 16, 2007, 12:38:41 PM »
hi i need explanation on why the lone pair of electron on nitrogen is in sp2 orbital for pyrdine but p orbital for pyrrole ???

THANKSS!!


also are the below underlined portions true (which i quoted from others)?

"Nitrogen as replacement heteroatom in benzene:
To formally replace a C atom of benzene, nitrogen must fulfill the same orbital and electronic criteria as the carbon it is to replace, i.e. it must be sp2-hybridised and have the same number of electrons (the principle of isoelectronic replacement).

Oxygen as replacement heteroatom in benzene:
For oxygen to achieve the same orbital and electronic requirements as a carbon in benzene it has to lose an electron becoming O+.

Sulphur as replacement heteroatom in benzene:
For sulphur to achieve the same orbital and electronic requirements as carbon it also has to lose an electron becoming S+.

what about thiopene then? it is S and not S+
« Last Edit: October 16, 2007, 01:26:37 PM by joanne »

Offline Yggdrasil

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Re: Nitrogen lone-pair in pyridine and pyrrole
« Reply #1 on: October 19, 2007, 10:20:14 PM »
hi i need explanation on why the lone pair of electron on nitrogen is in sp2 orbital for pyrdine but p orbital for pyrrole ???

Think about aromaticity.  Think about what orbitals are present on each atom in the ring.  Does pyridine have a p-orbital?  Is something already in it?

Quote
also are the below underlined portions true (which i quoted from others)?

"Nitrogen as replacement heteroatom in benzene:
To formally replace a C atom of benzene, nitrogen must fulfill the same orbital and electronic criteria as the carbon it is to replace, i.e. it must be sp2-hybridised and have the same number of electrons (the principle of isoelectronic replacement).

Oxygen as replacement heteroatom in benzene:
For oxygen to achieve the same orbital and electronic requirements as a carbon in benzene it has to lose an electron becoming O+.

Sulphur as replacement heteroatom in benzene:
For sulphur to achieve the same orbital and electronic requirements as carbon it also has to lose an electron becoming S+.

what about thiopene then? it is S and not S+

That sounds about right.  In the case of thiophene, thiophene is a five-membered ring, not a six-membered ring like benzene.

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