[katehovey]

Hi,

I need to know how to predict what positions will be nitrated on six aromatic molecules and also their rate relative to that of benzene. I've attached the six compounds below because I'm new to this forum and didn't know how to add a picture. Also, I'm having trouble naming all of them which obviously is making this research harder for me! I know the position depends on whether the substituted group is activating or deactivating but don't understand fully.

Thanks

[Yggdrasil]

Since the basic concepts behind activating/deactivating are hard to explain over the internet, I would suggest reading about it in your organic chemistry text first.  There may also be some good tutorials available on the web (example, wikipedia http://en.wikipedia.org/wiki/Electrophilic_aromatic_substitution#Substituted_aromatic_rings).  If you have more specific questions, we may be able to address them.

However, here is the basic concept.  Since the aromatic ring acts as a nucleophile in the any electrophilic aromatic substitution (EAS) reaction, substituents which increase the nucleophilicity of the ring are activating (increase the rate of reaction) and substituents which decrease the nucleophilicity of the ring are deactivating (decrease the rate of reaction).  Increasing/decreasing the nucleophilicity of the ring basically means whether the substituents adds electron density into the ring or takes it away (either by resonance or by the inductive effect).  Activating substituents are generally ortho-/para- dirrecting and deactivating substituents are generally meta-dirrecting (a exception is the halogens which are deactivating by ortho-/para-dirrecting).  For more in depth explanations, you would have to see your chemistry text, since I don't really have time to recapitulate the entire subject of EAS in this post.

[katehovey]

Thats great, I have read up on what you said already. Could you tell me the systematic names of the compounds? I'm struggling finding them on the internet and have no books with me. (I'm at home for the Easter break and left all my books in uni).

[Carcul]

From left to right: thioanisole, m-difenoxibenzene, p-chlorotoluene, ethyl p-etoxibenzoate, p-tert-butyltoluene, furan.

Positions expect to be nitrated: 2,4,6; 2,4; all four should be nitrated, with some predominance of nitration ortho to methyl group; ortho to methoxi group; ortho to methyl group, since tert-butyl is a large group; the outcome of furan nitration depends on what reagent you use to nitrate: for example, the usual mixture of nitric and sulphuric acids will decompose it, while acetyl nitrate will introduce a nitro group in position 2.

[Carcul]

In general, a substituent whose atom directly attached to the benzene ring has at least one unshared pair of electrons, and as long it doesn't carry a positive charge, is an activating one (the most common exceptions are the halogens and the nitroso group). So, the following groups are activating: -NH2, -NHR, -NR2, -OH, -OR, -SH, -SR. By "activating" we mean that the group activates the aromatic ring to electrophilic aromatic substitution: in other words, a benzene ring with an activating group will react faster than benzene in those reactions.
Deactivating groups are all those whose atom directly attached to the benzene ring has a partial, or total, positive charge: for example, -CHO, -COR, -CO2H, -CO2R, -NO2, -NR3+ -SO3H, -SO2R, -CH2CN, -CH=CHCN, and so on. A deactivating group makes reaction with an electrophile slower relative to benzene.

[AhmedEzatAlzawalaty]

dont forget that if a strongly activating group competes with weaker one or with a deactivating group the former controls

[katehovey]

Thank you so much. Really helpful.

Kate