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Hückel's rule can also be applied to molecules containing other atoms such as nitrogen or oxygen. For example pyridine (C 5 H 5 N) has a ring structure similar to benzene, except that one -CH- group is replaced by a nitrogen atom with no hydrogen. There are still six π electrons and the pyridine molecule is also aromatic and known for its ...
Every atom in the ring must have an occupied p orbital, which overlaps with p orbitals on either side (completely conjugated). Molecule must be planar. It must contain an odd number of pairs of pi electrons; must satisfy Hückel's rule: (4n+2) pi electrons, where n is an integer starting at zero.
Heteroarenes are aromatic compounds, where at least one methine or vinylene (-C= or -CH=CH-) group is replaced by a heteroatom: oxygen, nitrogen, or sulfur. [3] Examples of non-benzene compounds with aromatic properties are furan, a heterocyclic compound with a five-membered ring that includes a single oxygen atom, and pyridine, a heterocyclic compound with a six-membered ring containing one ...
when a ring with a circle is adjacent to a ring with two double bonds, an arrow is drawn from the former to the latter ring. Some results from these rules are worth being made explicit. Following Clar, [ 1 ] rules 1 and 2 imply that circles can never be in adjacent rings.
Both mechanisms are shown as follows for the ring contraction of biphenylene: The first involves a 1,2-hydrogen shift to a carbene followed by a 1,2-carbon shift on the same C-C bond but in opposite directions. The second differs from the first only by the order of the 1,2-shifts, with the 1,2-carbon shift preceding the 1,2-hydrogen shift.
Benzene, the model π system, has no permanent dipole moment, as the contributions of the weakly polar carbon–hydrogen bonds cancel due to molecular symmetry.However, the electron-rich π system above and below the benzene ring hosts a partial negative charge.
The simplest aryl group is phenyl, which is made up of a benzene ring with one of its hydrogen atom replaced by some substituent, and has the molecular formula C 6 H 5 −. Note that a phenyl group is not the same as a benzyl group, the latter consisting of a phenyl group attached to a methyl group and a molecular formula of C 6 H 5 CH 2 −. [2]
A diagram of an aromatic ring current. B 0 is the applied magnetic field, the red arrow indicating its direction. The orange ring shows the direction of the ring current, and the purple rings show the direction of the induced magnetic field. An aromatic ring current is an effect observed in aromatic molecules such as benzene and naphthalene.