Use Frost’s circle to construct orbital energy diagrams for (a) [10]annulene and (b) [12]a...

Use Frost’s circle to construct orbital energy diagrams for (a) [10]annulene and (b) [12]annulene. Is either aromatic according to Huckel’s rule?

Sample Solution (a) [10]Annulene is a ten-membered ring with five conjugated double bonds. Drawing a polygon with ten sides with its vertex pointing downward within a circle gives the orbital template. Place the orbitals at the positions where each vertex contacts the circle. The ten π electrons of [10]annulene satisfy the (4n + 2) rule for n = 2 and occupy the five bonding orbitals in pairs. [10]Annulene is aromatic according to Huckel’s rule.