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Author Topic: naphthalene derivatives aromatic substituion reactions  (Read 2691 times)

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sw2672

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naphthalene derivatives aromatic substituion reactions
« on: March 22, 2006, 02:45:57 PM »

Upon nitration, 1-naphthol (1-hydoxynaphthalene) yields 2,4-dinitronaphthol, while 1-nitronaphthalene yields 1,8-dinitronaphthalene and 1,5-dinitronaphthalene. How do you account for this contrast?
« Last Edit: March 22, 2006, 07:50:47 PM by sw2672 »
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Albert

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Re:naphthalene derivatives aromatic substituion reactions
« Reply #1 on: March 23, 2006, 01:50:09 AM »

Naphtalene monosubstituted derivatives have almost the same behaviour of benzene ones.

A basic rule says that the ring which undergoes the substitution reaction, is the more influenced by the first-added substituent.

Activating groups, such as OH, are ortho-para orientating, so the products of a nitration are supposed (and actually are) the ortho- PLUS the para- substituted derivative. Both can undergo a third reaction because, though a deactivating substituent, the nitro group is a meta orientating one.

On the other hand, deactivating groups, such as the aforementioned nitro one, direct an SEA reaction to the other ring, which doesn't 'suffer' the deactivating effect.
Most of the product you yield from nitration of 1-nitronaphthalene is the 1,8 derivative (approximately 60%), because of steric hindrance,  that makes easier a substitution in that very position.
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ankushbahl

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Re: naphthalene derivatives aromatic substituion reactions
« Reply #2 on: July 16, 2017, 11:35:04 PM »

A naphthalene molecule can be viewed as the fusion of a pair of benzene rings. (In organic chemistry, rings are fused if they share two or more atoms.) As such, naphthalene is classified as a benzenoid polycyclic aromatic hydrocarbon (PAH). There are two sets of equivalent hydrogen atoms: the alpha positions are numbered 1, 4, 5, and 8 (per diagram in right margin), and the beta positions, 2, 3, 6, and 7.

Unlike benzene, the carbon–carbon bonds in naphthalene are not of the same length. The bonds C1−C2, C3−C4, C5−C6 and C7−C8 are about 1.37 Å (137 pm) in length, whereas the other carbon–carbon bonds are about 1.42 Å (142 pm) long. This difference, established by X-ray diffraction, is consistent with the valence bond model in naphthalene and in particular, with the theorem of cross-conjugation. This theorem would describe naphthalene as an aromatic benzene unit bonded to a diene but not extensively conjugated to it (at least in the ground state).
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clarkstill

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Re: naphthalene derivatives aromatic substituion reactions
« Reply #3 on: July 17, 2017, 06:18:02 AM »

A naphthalene molecule can be viewed as the fusion of a pair of benzene rings. (In organic chemistry, rings are fused if they share two or more atoms.) As such, naphthalene is classified as a benzenoid polycyclic aromatic hydrocarbon (PAH). There are two sets of equivalent hydrogen atoms: the alpha positions are numbered 1, 4, 5, and 8 (per diagram in right margin), and the beta positions, 2, 3, 6, and 7.

Unlike benzene, the carbon–carbon bonds in naphthalene are not of the same length. The bonds C1−C2, C3−C4, C5−C6 and C7−C8 are about 1.37 Å (137 pm) in length, whereas the other carbon–carbon bonds are about 1.42 Å (142 pm) long. This difference, established by X-ray diffraction, is consistent with the valence bond model in naphthalene and in particular, with the theorem of cross-conjugation. This theorem would describe naphthalene as an aromatic benzene unit bonded to a diene but not extensively conjugated to it (at least in the ground state).

Thanks ankushbahl, but just copy/pasting from the wikipedia entry on naphthalene isn't tremendously helpful. Bizarrely you didn't even copy the section called 'Reactions with Electrophiles'...

sw2672 - you should really attempt the question before asking on here. Think about what the effect of electron-donating and electron-withdrawing groups are on regular electrophilic aromatic substitution reactions, using resonance arguments. Albert's answer is a good one though.
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wildfyr

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Re: naphthalene derivatives aromatic substituion reactions
« Reply #4 on: July 17, 2017, 11:20:44 AM »

Hey bud, this is from 2006 :). ankush, might be a bot
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clarkstill

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Re: naphthalene derivatives aromatic substituion reactions
« Reply #5 on: July 17, 2017, 09:29:58 PM »

Good spot. I wonder where sw2672 is now...
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