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Tutorial topics: Introduction Viewing Basics Molecular Shapes (VSEPR) Conformations Ethane Butane Cycloalkanes Substituted Cyclohexane Sterochemistry SN2 Reaction SN1 Reaction Aromaticity

Aromaticity Aromatic compounds are highly unsaturated, cyclic molecules that show extra stability as compared to their open chain counterpart. Huckel's rule for aromaticity states that a molecule must meet all of the following four conditions in order to be aromatic: 1) cyclic -- the molecule must be a cyclic polyene; 2) planar -- the geometry of the cyclic part must be planar; 3) each atom in the cyclic system must have a p orbital perpendicular to the ring; 4) the cyclic system has 4n+2 pi electrons. Benzene is an example of aromatic compounds. It meets all the above four conditions. In this tutorial, we will examine "live" molecules for their meeting geometry requirement (Condition 2).   This is the "live" molecule of benzene. Examine its structure for planarity. Benzene can also be called [6]-annulene. Shown below are some other cyclic polyenes that may or may not be aromatic. The number in the brackets indicates the number of double bond carbons. Examine their structures carefully to see if they meet all the four conditions for aromaticity. Which one(s) is(are) aromatic? [10]-annulene [14]-annulene [18]-annulene