Comments on: SOCl2 Mechanism For Alcohols To Alkyl Halides: SN2 versus SNi

By: Abhay

Abhay — Sat, 23 Mar 2024 14:10:29 +0000

Does it have something to do with the bulkyness of pyridine? I have been taught that in the presence of 3-R amine or pyridine SN2 occurs so the bulky nature seems like the only reasonable answer to why the chlorine is prevented from attacking from the same side to form a retention product rather than the inversion product. Am I right to assume this?

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By: Jaydeep

Jaydeep — Mon, 26 Oct 2020 05:14:52 +0000

I was taught that in Sni mechanism, a 4 membered cyclic Transition state is formed between S , O , Cl and R. Like this :
https://drive.google.com/file/d/1sxNy_jCMSCatIadoRnARrUGabNlvmpXA/view?usp=drivesdk

By: Vamsi

Vamsi — Sat, 29 Aug 2020 11:02:46 +0000

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By: Ambade Tushar

Ambade Tushar — Thu, 11 Jun 2020 19:27:19 +0000

Thanks a lot for detailed explanation . Also would like to say that I have read A topic onSNi reaction which is given in the reference book “Organic reactions: structure, mechanism” by Reinhard Bruckner.
It gives good insight how solvent Pyridine changes SNi route SN2 and why in solvent ether reaction of alcohol with thionyl chloride goes by SNi way.

By: Melissa

Melissa — Mon, 13 Apr 2020 02:44:59 +0000

I would be curious to hear your thoughts on the mechanism for converting a carboxylic acid to an acid chloride using SOCl2. I have seen mechanisms where it goes through a 6 membered TS for the first step and the second step while other mechanisms are more stepwise and use the chloride ion to attack.

By: James Ashenhurst

James Ashenhurst — Wed, 18 Sep 2019 19:51:18 +0000

In reply to sayan. Yes, other bases may be used. The advantage of pyridine in this case is that it is fairly weak (pka of conjugate acid is 4) and generally won't lead to competing E2 reactions of the resulting alkyl halides. Tertiary amines are stronger bases, with a pKa (of the conjugate acid) of about 10 or so, so elimination starts to become more of a problem.

By: James Ashenhurst

James Ashenhurst — Thu, 13 Jun 2019 19:33:38 +0000

In reply to Krishna. Internal return of the leaving group as a nucleophile. Doesn't really fall into either category.

By: James Ashenhurst

James Ashenhurst — Thu, 13 Jun 2019 13:55:26 +0000

In reply to Bhabani. No, PCl5 will just do SN2.

By: James Ashenhurst

James Ashenhurst — Thu, 13 Jun 2019 13:55:04 +0000

In reply to hari. Likely a plain old SN2.