Lecture07outline

Lecture07outline - I Review Aromatic molecules absorb UV light but the HOMOLUMO gap is fairly large and the max is <200 nm for benzene max

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I. Review • Aromatic molecules absorb UV light, but the HOMO–LUMO gap is fairly large and the λ max is <200 nm for benzene λ max increases when electron donating and/or withdrawing groups are added to the molecule because they diminish the HOMO–LUMO gap • Aromatic rings do not fragment in MS experiments because of the instability of phenyl radicals and cations, but benzylic fragmentations are common • Aromatic molecules do not show similar reactivity to alkenes due to the energetic penalty (~33 kcal/mol) of breaking aromaticity • Aromaticity can be broken transiently, as demonstrated by the incorporation of deuterium into benzene by DBr • The process in which a strong electrophile reacts with an aromatic molecule then a proton is lost to regenerate aromaticity and form a substituted arene is called electrophilic aromatic substitution (EAS) • All EAS reactions proceed through the same mechanism, the only difference is in the generation of the electrophile • Aryl halides can be prepared by reacting with Cl
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This note was uploaded on 05/17/2010 for the course CHEM 0740 taught by Professor Professor during the Spring '10 term at Pittsburgh.

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Lecture07outline - I Review Aromatic molecules absorb UV light but the HOMOLUMO gap is fairly large and the max is <200 nm for benzene max

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