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#1 2010-10-14 03:47:30

skyknight81
Guest

Aromatic Character of Protonated Furan

Hi,

We know that protonated pyrrole is non-aromatic as the lone pair of nitrogen is not available anymore. But in the case of protonated furan, what can we say about the aromatic character of the compound ? Is it aromatic or non-aromatic ?

Regards,

Harpreet

 

#2 2010-10-14 04:29:44

orgopete
Administrator

Re: Aromatic Character of Protonated Furan

It will still be aromatic as the molecule will still prefer being aromatic. That is, protonation can occur on either non-bonded electrons, the aromatic or the non-aromatic pair (they really are the same though). However, the non-aromatic electrons will allow the ring to remain aromatic, the energetically preferred form.

However, just as electrophilic reactions of furan occur on carbon, if protonation occurs on carbon, the protonated form will be non-aromatic.

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#3 2010-10-15 01:17:24

skyknight81
Guest

Re: Aromatic Character of Protonated Furan

Continuing in succession to the above topic where I talked about a protonated furan being aromatic or non-aromatic, I wish to discuss the nucleophilic nature of oxygen in furan.

http://farm5.static.flickr.com/4129/5082599505_838637a1f3.jpg

What can be said about the feasibility of the above reaction ? Is it a valid intramolecular nucleophilic substitution reaction (neighbouring group participation or anchimeric assistance) ?

Regards

Harpreet

 

#4 2010-10-16 14:51:21

orgopete
Administrator

Re: Aromatic Character of Protonated Furan

While that is an interesting structure to create, we must also remain cognizant of innate reactivity of an alkyl chloride. For example, tetrahydrofuran does not react with methyl iodide to any notable amount. Thus, THF can be used as the solvent in alkylation reactions. If the oxygen were attached to an electron withdrawing sp2-carbon, it will further reduce the reactivity. Then, lets add a less reactive chloride and this should indicate that this cyclization is not likely to occur because of low reactivity.

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