Help With Substitution question.
Chemistry discussion, revision, exam and homework help.
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Help With Substitution question.[IMG]
Chemistry Question by limetang, on Flickr[/IMG]
My issue is figuring out what the mechanism is that forms the intermediate.Last edited by limetang; 11-05-2012 at 00:31. -
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Re: Help With Substitution question.Have you come across tosyl chloride before? It's a simple addition-elimination by the alcohol attacking the S=O pi* and then reformation of the double bond with loss of Cl-. The carbon with the OH on keeps the same stereochemistry as it had before the tosylation as it is not touched, but then is inverted by the Sn2 reaction which follows.(Original post by limetang)
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Chemistry Question by limetang, on Flickr[/IMG]
My issue is figuring out what the mechanism is that forms the intermediate.
Tosylation is a common way of turning OH (a poor leaving group) into a very good one. -
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Re: Help With Substitution question.No.(Original post by limetang)
Would I be right in thinking that it is E2, and that the molecule on the top of the arrow attacks an antiperiplanar hydrogen through one of the oxygens resulting in an alkene. And after this the CN- is added to the alkene.
The hydroxy lone pair attacks the S=O bond in exactly the same way you'd have it attacking an acid chloride. -
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Re: Help With Substitution question.Okay. Thanks.(Original post by illusionz)
No.
The hydroxy lone pair attacks the S=O bond in exactly the same way you'd have it attacking an acid chloride.
So. Analogous to this:
???
And essentially I assume that once this first step has been done it increases the rate of substitution with cyanide by replacing the OH with a better leaving group. Correct?Last edited by limetang; 11-05-2012 at 00:46. -
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Re: Help With Substitution question.Yep that's the mechanism. The whole species is often abbreviated TsCl for the toluenesulphonyl chloride, and OTs for the leaving group. OH is a very poor leaving group unless you are under basic conditions. OTS is a lot, lot better.(Original post by limetang)
Okay. Thanks.
So. Analogous to this:
???
And essentially I assume that once this first step has been done it increases the rate of substitution with cyanide by replacing the OH with a better leaving group. Correct?
