answers to sec11_24

answers to sec11_24 - Extension of Hückel's Rule Pyridine...

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Unformatted text preview: Extension of Hückel's Rule Pyridine 6 ____ π electrons for 3 double bonds. Satisfies (4n+2) rule already. A heteroatom such as O or N can contribute 0 2 either ___ or ___ of its unshared electrons as needed ____________ to the π system so as to satisfy (4n + 2) the _________ π electron requirement. 11.24 Heterocyclic Aromatic Compounds and N •• 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 ring; Or: 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 p 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; Is _____ part of π system of ring. LOU sp2 Overall, heteroatom is ____ hybridized. more Pyridine is 107 – 109 times _____ basic than pyrrole. pyrrole. N •• •• N Furan five Two ____ Ns in a _____-membered ring. _____2 Draw Robinson structure? not in N-1 is ______ a double bond, and p has a lone pair in a ___ orbital and is ______ part of ring π system pyrrole (_________-like unshared pair); (_________- •• O •• in N-2 is ______ a double bond and sp2 has a lone pair in an ___ orbital and is not part of ring π system ______ pyridine (_________-like unshared pair) (_________- Two _____ lone pairs on oxygen. p One pair is in a ___ orbital and is ______ part of ring π system; 2 contributes ___ electrons to the π system; sp2 The other pair is in an ___ orbital is not and ______ part of ring π system; extra 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 sp2 hybridized _____________ orbital (localized on N); not ______ 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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This note was uploaded on 10/05/2009 for the course CEE 11024155 taught by Professor Xia during the Winter '08 term at UCLA.

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