CHEM 2211 1nd Edition Lecture 26 Outline of Last Lecture I Midterm Outline of Current Lecture I Aromaticity Current Lecture Aromaticity Aromatic compounds Are compounds with large delocalization energies What does this really mean To know this we must look at the criteria for being aromatic A compound must meet two criteria to be considered and labeled aromatic 1 It must have an uninterrupted cyclic could of pie electrons above an below the plane of the molecule a For the pie cloud to be cyclic the molecule must be cyclic b For the pie cloud to be uninterrupted every atom in the ring must have a p orbital c For the cloud to form each p orbital must over lap the p orbital on either side of it As a result the molecule must be planar 2 The pie cloud must contain an odd number of pairs of pie electrons These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Testing for Aromaticity Cyclopentadiene cyclopentadienyl cation Cyclopentadienyl anion Cyclopentadiene is not aromatic Because it does not satisfy the first criteria for being aromatic This is because it has an sp3 hybridized carbon o An only sp2 carbons an sp carbons have bearing atoms Cyclcopentadienyl cation is not atomatic Because it does have an uninterrupted ring of p orbital bearing electrons But it has an even number of double bonds o Which breaks the second criteria for being aromatic Cyclopentadienyl anion is aromatic Because it does have an uninterrupted ring of p orbital bearing electrons The pie cloud contains an odd number pair of delocalized pie electrons
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