14 Aromaticity

14 Aromaticity - Aromaticity or Anti-aromaticity (revised...

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Unformatted text preview: Aromaticity or Anti-aromaticity (revised March 15, 2010) Introduction: Aromatic or anti-aromatic rings must: 1) Have a continuous ring of SP2 or SP atoms. 2) The ring must be Fat (so all the P-orbitals can line up). 3) The total number of pi-electrons will be: 4n + 2 for aromatic systems 4n for antiaromatic systems 2) If a fully conjugated ring is Fat, then all the p-orbitals on each atom can line up allowing the pi- electrons a continous path around the ring. A non-planar geomety will break the alignment of the p-orbitals and will break conjugation. 1) Conjugation can be broken by a SP3 atom such as a methylene (CH 2 ) or by a break in the sigma (single bond) framework. N H 3 C CH 3 CH 2 is SP3 This is not a ring N is SP3 These cannot be aromatic or antiaromatic because: The most difcult type of SP2 atoms to recognize are the ones with lone pairs. These can look like they are SP3 but then are SP2 in another resonance structure. In these cases, we consider them SP2. Here are some examples:...
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This note was uploaded on 02/20/2012 for the course CHEM 334 taught by Professor Wang during the Spring '09 term at South Carolina.

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14 Aromaticity - Aromaticity or Anti-aromaticity (revised...

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