September 23, 2021, 02:32:37 AM
Forum Rules: Read This Before Posting


Topic: Write a mechanism for this rxn  (Read 9017 times)

0 Members and 1 Guest are viewing this topic.

Offline saN

  • Regular Member
  • ***
  • Posts: 62
  • Mole Snacks: +0/-1
  • Gender: Male
Write a mechanism for this rxn
« on: November 22, 2007, 04:19:17 PM »


Here is what I came up with. Is this correct?


Offline ultrashogun

  • Regular Member
  • ***
  • Posts: 58
  • Mole Snacks: +5/-6
Re: Write a mechanism for this rxn
« Reply #1 on: November 22, 2007, 04:49:06 PM »
Yeah thats it, only that the attack of the double bond on Br2 forms a 3 membered bromonium ion, but attack still happens where you said it would because the more substituted carbon carries more partil charge.

Offline Nick.Sparrow

  • Regular Member
  • ***
  • Posts: 16
  • Mole Snacks: +0/-0
Re: Write a mechanism for this rxn
« Reply #2 on: November 22, 2007, 04:55:29 PM »
Everything is simple!
First, bromine is added on double bond, second nucleophilic substitution of the corresponding bromine anion by the hydroxygroup
Visit a web site on Microwave Chemistry & Equipment
www.microwavetec.com

Offline Nick.Sparrow

  • Regular Member
  • ***
  • Posts: 16
  • Mole Snacks: +0/-0
Re: Write a mechanism for this rxn
« Reply #3 on: November 22, 2007, 05:04:37 PM »
that is!
Visit a web site on Microwave Chemistry & Equipment
www.microwavetec.com

Offline ultrashogun

  • Regular Member
  • ***
  • Posts: 58
  • Mole Snacks: +5/-6
Re: Write a mechanism for this rxn
« Reply #4 on: November 22, 2007, 05:10:51 PM »
Everything is simple!
First, bromine is added on double bond, second nucleophilic substitution of the corresponding bromine anion by the hydroxygroup


Are you sure about the substitution? Because I know that water can attack the bromonium ion, shouldnt the hydroxy group also be able to do so?

Offline Nick.Sparrow

  • Regular Member
  • ***
  • Posts: 16
  • Mole Snacks: +0/-0
Re: Write a mechanism for this rxn
« Reply #5 on: November 22, 2007, 05:30:21 PM »
Quote
Are you sure about the substitution?

Yes!
Nobody've seen it, but many believe...
Visit a web site on Microwave Chemistry & Equipment
www.microwavetec.com

Offline Dan

  • Retired Staff
  • Sr. Member
  • *
  • Posts: 4716
  • Mole Snacks: +467/-72
  • Gender: Male
  • Organic Chemist
    • My research
Re: Write a mechanism for this rxn
« Reply #6 on: November 22, 2007, 07:33:02 PM »
that is!

I don't agree with this mechanism, I'm with ultrashogun (see below). I think that ring closure occurs by intramolecular attack of the hydroxyl on the bromonium ion. The intramolecular opening of the bromonium ion should be faster than the intermolecular opening with bromide. Unless you are in base and can deprotonate your alcohol I expect the Sn2 on the dibromoalkane will be very, very slow.

I realise it's just a typo, but you're missing a carbon in your starting material

My research: Google Scholar and Researchgate

Offline cetirizine

  • Regular Member
  • ***
  • Posts: 10
  • Mole Snacks: +0/-0
Re: Write a mechanism for this rxn
« Reply #7 on: November 22, 2007, 08:15:01 PM »
that is!

I don't agree with this mechanism, I'm with ultrashogun (see below). I think that ring closure occurs by intramolecular attack of the hydroxyl on the bromonium ion. The intramolecular opening of the bromonium ion should be faster than the intermolecular opening with bromide. Unless you are in base and can deprotonate your alcohol I expect the Sn2 on the dibromoalkane will be very, very slow.

I realise it's just a typo, but you're missing a carbon in your starting material



I agree with you, I think you are right

Offline Nick.Sparrow

  • Regular Member
  • ***
  • Posts: 16
  • Mole Snacks: +0/-0
Re: Write a mechanism for this rxn
« Reply #8 on: November 23, 2007, 04:25:26 AM »
that is!

I don't agree with this mechanism, I'm with ultrashogun (see below). I think that ring closure occurs by intramolecular attack of the hydroxyl on the bromonium ion. The intramolecular opening of the bromonium ion should be faster than the intermolecular opening with bromide. Unless you are in base and can deprotonate your alcohol I expect the Sn2 on the dibromoalkane will be very, very slow.

I realise it's just a typo, but you're missing a carbon in your starting material



Yea, you are right! There should be the bromonium intermediate (J. Org. Chem., Vol. 61, No. 3, 1996), but to be absolutely correct, it must be stabilized by some additional ligands.
Visit a web site on Microwave Chemistry & Equipment
www.microwavetec.com

Offline RBF

  • Regular Member
  • ***
  • Posts: 45
  • Mole Snacks: +4/-0
Re: Write a mechanism for this rxn
« Reply #9 on: November 23, 2007, 10:47:30 AM »
A more fundamental problem with the original mechanism is that it has the bromine attacking as a nucleophile.  Look at the direction of the arrow.  This would result in a carbanion rather than a carbocation in the intermediate.  The bromonium ion intermediate postulated by Dan and others is correct.

Offline saN

  • Regular Member
  • ***
  • Posts: 62
  • Mole Snacks: +0/-1
  • Gender: Male
Re: Write a mechanism for this rxn
« Reply #10 on: November 23, 2007, 12:51:33 PM »
The mechanism Dan drew is with a bromonium ion intermediate and than the hydroxyl group attacks to form the ring.
 
What program are you using to draw these mechanisms? I do it by hand and scan them, which can be sloppy.
« Last Edit: November 23, 2007, 06:14:47 PM by saN »

Offline ultrashogun

  • Regular Member
  • ***
  • Posts: 58
  • Mole Snacks: +5/-6
Re: Write a mechanism for this rxn
« Reply #11 on: November 23, 2007, 02:37:51 PM »
The mechanism Dan drew is with a bromonium ion intermediate and than the hydroxyl group attacks to form the ring.
 
What program are you using to draw these mechanisms? I do it by hand and scan them, which can be a PITA.

I enjoyed the scanned picture, gives it more personality!

Offline Nick.Sparrow

  • Regular Member
  • ***
  • Posts: 16
  • Mole Snacks: +0/-0
Re: Write a mechanism for this rxn
« Reply #12 on: November 23, 2007, 07:20:50 PM »

What program are you using to draw these mechanisms? I do it by hand and scan them, which can be sloppy.

I used ISIS drow, but the best is ChemDrow from ChemOffice packet, but hand drowing looks nice on the computer screen  :D
Visit a web site on Microwave Chemistry & Equipment
www.microwavetec.com

Sponsored Links