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Week 4-July 18 - Week 4 Benzene and its Derivatives Draw...

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Week 4 July 1 8 , 201 1 Benzene and its Derivatives Draw the structures of the following molecules: toluene m -chlorophenol nitrobenzene p -nitroaniline o -chloroanisole Reading : Section 16.1 1
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Week 4 July 18, 2011 2 Aromaticity: More Than Just Conjugation In the 19th century, benzene was quite a puzzle. In 1865, Kekulé proposed the now- familiar structure for benzene that we might call “1,3,5-cyclohexatriene.” This structure was quite controversial because the Kekulé structure suggests that there should be four isomeric dibromobenzenes, while there are in fact only three : benzene 1,2-dibromobenzene ( ortho ) 2,3-dibromobenzene ( ortho ) 1,3-dibromobenzene ( meta ) 1,4-dibromobenzene ( para ) Br Br Br Br Br Br Br Br the same molecule? Of course, we know that there is only one ortho dibromobenzene. How can that be? Benzene is an example of an aromatic compound. The criteria for aromaticity are: - The molecule must contain a contiguous , planar, cyclic arrangement of p -orbitals. - The arrangement of p -orbitals must contain 4n+2 electrons, where n = 0, 1, 2, ... Aromatic compounds are especially stable .
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