# Is biphenyl considered to be aromatic?

Biphenyl has 12 π-electrons and according to Hückel’s rule, it should not be aromatic because $12 \neq 4n+2$, but it nevertheless is aromatic. Why is that so?

• @henry It isn't a single aromatic system but two independent ones (there is mostly free rotation around the c-c bond that joins the two rings). May 20, 2016 at 8:24
• Huckel's rule only applies to monocyclic systems without side groups. In fact, this rule is so frequently misused I'd rather have people forget about it altogether. May 20, 2016 at 8:38
• I see no point in such a modification. How would you know when to apply it and when not to? Will it work with corannulene, for example? (It will not.) No, stick to the Huckel's rule when it is applicable, and when it is not, resort to the more complicated math (finding the eigenvalues, etc). Alternatively, you can point out that in the real biphenyl molecule the rings are twisted (non-coplanar), and hence not conjugated, so that each $\pi$ system is pretty much on its own. May 20, 2016 at 8:56
• @Henry Pyrene is a fused-ring system which is why you need more sophisticated rules about aromaticity. That isn't needed here as the two rings are not fused and can be treated independently due to the relatively free rotation about the linking bond (strictly there is a small steric barrier to rotation which results in a preferred confirmation where the rings are ~40 degrees from being planar, which also implies they are two separate aromatic systems and not one single one.) May 20, 2016 at 8:57
• Math does apply in chemistry, but... Well, see this: en.wikipedia.org/wiki/H%C3%BCckel_method May 20, 2016 at 8:59