Search results
Results from the WOW.Com Content Network
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.
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.
The NMR signal of protons in the plane of an aromatic ring are shifted substantially further down-field than those on non-aromatic sp² carbons. This is an important way of detecting aromaticity. By the same mechanism, the signals of protons located near the ring axis are shifted up-field.
Generally the aromatic protons appear near their usual positions around 7.2 ppm, indicating that even with severe distortions, the ring retains aromaticity. The central methylene protons in the aliphatic bridge are shielded to a position of around - 0.5 ppm. [6]
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 ...
[2] The bond lengths between carbon atoms in a phenyl group are approximately 1.4 Å. [6] In 1 H-NMR spectroscopy, protons of a phenyl group typically have chemical shifts around 7.27 ppm. These chemical shifts are influenced by aromatic ring current and may change depending on substituents.
Michelle, 60, has often sat near former President Bush, 78, at other public events in which all living presidents gather, such as funerals for high-profile U.S. politicians.
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 − .