intaroma_key - OWLS: Introduction to Aromaticity Solutions...

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Unformatted text preview: OWLS: Introduction to Aromaticity Solutions 1 OWLS: Introduction to Aromaticity Solutions 1. Similarities : Conjugation and aromaticity both provide special stabilization relative to nonconjugated or nonaromatic isomers. Both involve extended pi electron systems, featuring parallel and overlapping p orbitals. Both require that the atoms bearing the p orbitals of the pi electron cloud to be planar, in order to maximize the overlap of these adjacent p orbitals. Differences : The p orbitals that overlap to form the π molecular orbitals of an aromatic molecule must be in a continuous loop whereas conjugated molecules may be cyclic or acyclic. An aromatic molecule incorporates 4n + 2 pi electrons whereas a conjugated molecule does not have this restriction. Other similarities and differences exist. 2. (a) Phenanthrene has a closed loop of p orbitals (the circled atoms shown below), and no significant strain issues that prevent planarity. It has fourteen pi electrons (n = 3). Therefore phenanthrene is aromatic. (b) Two sp 3 carbons interrupt the p orbital loop, so Dewar benzene is not aromatic. ...
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