Unformatted text preview: Extension of Hückel's Rule Pyridine
____ π electrons for 3 double bonds.
Satisfies (4n+2) rule already. A heteroatom such as O or N can contribute
either ___ or ___ of its unshared electrons
____________ to the π system so as to satisfy
(4n + 2)
the _________ π electron requirement. 11.24
Heterocyclic Aromatic Compounds
•• Hückel's Rule LOU LOU 4
____ π electrons for 2 double bonds. Either:
in a double bond
(1) it is _______________:
lone pair is in sp2 orbital, not
contributed to the π system of
not in a double bond
(2) it is__________________: 2
needs __ more to satisfy (4n+2) rule.
•• N 2
N needs to contribute ___ electrons H to the π system.
Therefore, lone pair on N must be in
a ___ orbital (delocalized) in order to but contributes the lone pair in a
p-orbital to the π system overlap with the π system of ring;
_____ part of π system of ring.
Overall, heteroatom is ____ hybridized. more
Pyridine is 107 – 109 times _____ basic than pyrrole.
•• •• N Furan five
____ Ns in a _____-membered ring.
_____2 Draw Robinson
structure? not in
N-1 is ______ a double bond, and
has a lone pair in a ___ orbital and
______ part of ring π system
(_________-like unshared pair);
(_________- •• O
N-2 is ______ a double bond and
has a lone pair in an ___ orbital and
is not part of ring π system
(_________-like unshared pair)
_____ lone pairs on oxygen.
One pair is in a ___ orbital and
______ part of ring π system;
contributes ___ electrons to the π
The other pair is in an ___ orbital
and ______ part of ring π system;
an “______” pair, not needed for
aromatic stabilization. LOU not
Unshared pair of N are ____ part of the π system
of ring and ______________ in bonding with H
can be involved
while leaving the aromatic π system intact H
LOU Imidazole LOU Comparing Basicities of Pyridine and Pyrrole LOU 1 to the π system.
Therefore, lone pair on N is in an
_____________ orbital (localized on N);
______ part of π system of ring. LOU Role of the Heteroatom in the π System Pyrrole 0
N needs to contribute ___ electrons ...
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- Winter '08
- Electron, Lone pair, Delocalized electron, double bond