Aromatic ring current | Wikipedia audio article
Channel: wikipedia tts
Date: 13/12/2018

This is an audio version of the Wikipedia Article:
Aromatic ring current


00:02:10 1 Relative aromaticity
00:02:41 1.1 Nucleus-independent chemical shift
00:03:00 1.2 Harmonic oscillator model of aromaticity
00:03:49 2 References
00:04:22 undefined



Listening is a more natural way of learning, when compared to reading. Written language only began at around 3200 BC, but spoken language has existed long ago.

Learning by listening is a great way to:
- increases imagination and understanding
- improves your listening skills
- improves your own spoken accent
- learn while on the move
- reduce eye strain

Now learn the vast amount of general knowledge available on Wikipedia through audio (audio article). You could even learn subconsciously by playing the audio while you are sleeping! If you are planning to listen a lot, you could try using a bone conduction headphone, or a standard speaker instead of an earphone.

You can find other Wikipedia audio articles too at:
https://www.youtube.com/channel/UCuKfABj2eGyjH3ntPxp4YeQ

You can upload your own Wikipedia articles through:
https://github.com/nodef/wikipedia-tts



"The only true wisdom is in knowing you know nothing."
- Socrates



SUMMARY
=======
An aromatic ring current is an effect observed in aromatic molecules such as benzene and naphthalene. If a magnetic field is directed perpendicular to the plane of the aromatic system, a ring current is induced in the delocalized π electrons of the aromatic ring. This is a direct consequence of Ampère's law; since the electrons involved are free to circulate, rather than being localized in bonds as they would be in most non-aromatic molecules, they respond much more strongly to the magnetic field.
The ring current creates its own magnetic field. Outside the ring, this field is in the same direction as the externally applied magnetic field; inside the ring, the field counteracts the externally applied field. As a result, the net magnetic field outside the ring is greater than the externally applied field alone, and is less inside the ring.
Aromatic ring currents are relevant to NMR spectroscopy, as they dramatically influence the chemical shifts of 1H nuclei in aromatic molecules.  The effect helps distinguish these nuclear environments and is therefore of great use in molecular structure determination. In benzene, the ring protons experience deshielding because the induced magnetic field has the same direction outside the ring as the external field and their chemical shift is 7.3 ppm compared to 5.6 for the vinylic proton in cyclohexene. In contrast any proton inside the aromatic ring experiences shielding because both fields are in opposite direction. This effect can be observed in cyclooctadecanonaene ([18]annulene) with 6 inner protons at −3 ppm.
The situation is reversed in antiaromatic compounds. In the dianion of [18]annulene the inner protons are strongly deshielded at 20.8 ppm and 29.5 ppm with the outer protons significantly shielded (with respect to the reference) at −1.1 ppm. Hence a diamagnetic ring current or diatropic ring current is associated with aromaticity whereas a paratropic ring current signals antiaromaticity.
A similar effect is observed in three-dimensional fullerenes; in this case it is called a sphere current.