October 21, 2021, 07:23:42 AM
Forum Rules: Read This Before Posting


Topic: How do I solve for these Alkene and Epoxide Chemistry problems? :(  (Read 10122 times)

0 Members and 1 Guest are viewing this topic.

Offline newkiddonblock

  • Regular Member
  • ***
  • Posts: 21
  • Mole Snacks: +1/-2
Re: How do I solve for these Alkene and Epoxide Chemistry problems? :(
« Reply #15 on: December 08, 2012, 01:01:35 PM »
What would methanolic HBr solution give you?

You mean an epoxide reaction with HBr and methanol?

Offline discodermolide

  • Chemist
  • Sr. Member
  • *
  • Posts: 5038
  • Mole Snacks: +404/-70
  • Gender: Male
    • My research history
Re: How do I solve for these Alkene and Epoxide Chemistry problems? :(
« Reply #16 on: December 08, 2012, 01:09:39 PM »
Yes.
Development Chemists do it on Scale, Research Chemists just do it!
My Research History

Offline newkiddonblock

  • Regular Member
  • ***
  • Posts: 21
  • Mole Snacks: +1/-2

Offline newkiddonblock

  • Regular Member
  • ***
  • Posts: 21
  • Mole Snacks: +1/-2
Re: How do I solve for these Alkene and Epoxide Chemistry problems? :(
« Reply #18 on: December 08, 2012, 01:37:43 PM »
Wait but you didn't answer my question though :(

Was using Br2 to attack the less sterically hindered carbon correct/incorrect?

Offline orgopete

  • Chemist
  • Sr. Member
  • *
  • Posts: 2636
  • Mole Snacks: +213/-71
    • Curved Arrow Press
Re: How do I solve for these Alkene and Epoxide Chemistry problems? :(
« Reply #19 on: December 08, 2012, 02:08:10 PM »
Hint, methylcyclohexene plus Br2/H2O gives 2-bromo-1-methylcyclohexanol with the bromo and hydroxyl trans.
Author of a multi-tiered example based workbook for learning organic chemistry mechanisms.

Offline newkiddonblock

  • Regular Member
  • ***
  • Posts: 21
  • Mole Snacks: +1/-2
Re: How do I solve for these Alkene and Epoxide Chemistry problems? :(
« Reply #20 on: December 08, 2012, 02:09:43 PM »
Hint, methylcyclohexene plus Br2/H2O gives 2-bromo-1-methylcyclohexanol with the bromo and hydroxyl trans.

For which one?

Offline orgopete

  • Chemist
  • Sr. Member
  • *
  • Posts: 2636
  • Mole Snacks: +213/-71
    • Curved Arrow Press
Re: How do I solve for these Alkene and Epoxide Chemistry problems? :(
« Reply #21 on: December 08, 2012, 02:14:23 PM »
Hint, methylcyclohexene plus Br2/H2O gives 2-bromo-1-methylcyclohexanol with the bromo and hydroxyl trans.

For which one?
That illustrates a principle that needs to be applied. What reagents answers #1? That should help to answer #2.
Author of a multi-tiered example based workbook for learning organic chemistry mechanisms.

Offline newkiddonblock

  • Regular Member
  • ***
  • Posts: 21
  • Mole Snacks: +1/-2
Re: How do I solve for these Alkene and Epoxide Chemistry problems? :(
« Reply #22 on: December 08, 2012, 02:18:58 PM »
Hint, methylcyclohexene plus Br2/H2O gives 2-bromo-1-methylcyclohexanol with the bromo and hydroxyl trans.

For which one?
That illustrates a principle that needs to be applied. What reagents answer #1? That should help to answer #2.

1st one: HBr and H3CCO3H

That's what confuses me for the second one because the answers says:

Br2/H3COH

???

What about H3CCO3H?? Is that not in there as well? I thought this was also an epoxidation reaction.

Offline orgopete

  • Chemist
  • Sr. Member
  • *
  • Posts: 2636
  • Mole Snacks: +213/-71
    • Curved Arrow Press
Re: How do I solve for these Alkene and Epoxide Chemistry problems? :(
« Reply #23 on: December 08, 2012, 02:30:22 PM »
The first one is to make the epoxide first. Open the epoxide with HBr because Br2/H2O gives the opposite isomer. Opening a bromonium results in attack at the more stable carbocation. If methanol replaces water, then methanol can attacked the bromonium ion at the more stable carbocation position.

Nucleophilic opening are sensitive to steric effects.
Author of a multi-tiered example based workbook for learning organic chemistry mechanisms.

Offline newkiddonblock

  • Regular Member
  • ***
  • Posts: 21
  • Mole Snacks: +1/-2
Re: How do I solve for these Alkene and Epoxide Chemistry problems? :(
« Reply #24 on: December 08, 2012, 03:04:11 PM »
The first one is to make the epoxide first. Open the epoxide with HBr because Br2/H2O gives the opposite isomer. Opening a bromonium results in attack at the more stable carbocation. If methanol replaces water, then methanol can attacked the bromonium ion at the more stable carbocation position.

Nucleophilic opening are sensitive to steric effects.

Wait wait...i have to visualize this...The part I bolded...you're talking about the second one right?

Offline newkiddonblock

  • Regular Member
  • ***
  • Posts: 21
  • Mole Snacks: +1/-2
Re: How do I solve for these Alkene and Epoxide Chemistry problems? :(
« Reply #25 on: December 08, 2012, 03:17:02 PM »
The first one is to make the epoxide first. Open the epoxide with HBr because Br2/H2O gives the opposite isomer. Opening a bromonium results in attack at the more stable carbocation. If methanol replaces water, then methanol can attacked the bromonium ion at the more stable carbocation position.

Nucleophilic opening are sensitive to steric effects.

Ok I'm lost :(

Can you tell me step by step where things go in the second reaction (the diagram I drew)

Offline newkiddonblock

  • Regular Member
  • ***
  • Posts: 21
  • Mole Snacks: +1/-2
Re: How do I solve for these Alkene and Epoxide Chemistry problems? :(
« Reply #26 on: December 08, 2012, 03:30:39 PM »
Oh my God this is getting more and more confusing...

Ok ok...
I'm a very logical thinker and I need to put all this stuff into steps rather than a paragraph (if you don't mind)

First thing first, WHICH one attacks the less sterically hindered carbon at the bottom? methanol or Br-?
Because these are my notes for epoxidation reactions with BASES (from many youtube videos)

1) the nucleophile readily attacks the less substituted carbon atom
2) the C-O bond at THAT site is broken and a ring opened species is formed
3) the oxygen is then protonated by the conjugate acid of the nucleophile (?)
4) You end up with a final ring opened product with the nucleophile at the bottom right corner, and the OH on the top

If that's right, then how do I translate that into what you just said and into pictures.

Focusing on the second reaction
1) Br2 is Br+ + Br-
2) Br-, the nucleophile, attacks the less sterically hindered carbon (the most stable), but the ring can only be opened by an H atom (according to the user "discoder"???)

Offline orgopete

  • Chemist
  • Sr. Member
  • *
  • Posts: 2636
  • Mole Snacks: +213/-71
    • Curved Arrow Press
Re: How do I solve for these Alkene and Epoxide Chemistry problems? :(
« Reply #27 on: December 08, 2012, 04:56:00 PM »
Oh my God this is getting more and more confusing...

Ok ok...
I'm a very logical thinker and I need to put all this stuff into steps rather than a paragraph (if you don't mind)

First thing first, WHICH one attacks the less sterically hindered carbon at the bottom? methanol or Br-?
Because these are my notes for epoxidation reactions with BASES (from many youtube videos)

1) the nucleophile readily attacks the less substituted carbon atom
2) the C-O bond at THAT site is broken and a ring opened species is formed
3) the oxygen is then protonated by the conjugate acid of the nucleophile (?)
4) You end up with a final ring opened product with the nucleophile at the bottom right corner, and the OH on the top

If that's right, then how do I translate that into what you just said and into pictures.

Focusing on the second reaction
1) Br2 is Br+ + Br-
2) Br-, the nucleophile, attacks the less sterically hindered carbon (the most stable), but the ring can only be opened by an H atom (according to the user "discoder")

I too am becoming confused by the above. Reaction 1 and 2 are electrophile controlled and 3 & 4 are nucleophile controlled. If electrophile controlled (SN1-like), then nucleophile attacks carbon best able to stabilize carbocation (even if a bromonium, protonated epoxide, or other equivalents). If nucleophile controlled (SN2-like), the steric hindrance controls regio and stereochemistry. Attack at least substituted carbon.
« Last Edit: December 08, 2012, 05:49:46 PM by orgopete »
Author of a multi-tiered example based workbook for learning organic chemistry mechanisms.

Offline newkiddonblock

  • Regular Member
  • ***
  • Posts: 21
  • Mole Snacks: +1/-2
Re: How do I solve for these Alkene and Epoxide Chemistry problems? :(
« Reply #28 on: December 08, 2012, 05:04:30 PM »

I too am becoming confused by the above. Reaction 1 and 2 are electrophile controlled and 3 & 4 are nucleophile controlled. If electrophile controlled (SN1-like), then nucleophile attacks carbon best able to stabilize carbocation (even if a bromonium, protonated epoxide, or other equivalents). If nucleophile controlled (SN2-like), the steric hindrance controls regio and stereochemistry. Attack at least substituted carbon.

I'm asking if you could clarify the pushing mechanism for me...
Hold on let me upload a picture

Offline newkiddonblock

  • Regular Member
  • ***
  • Posts: 21
  • Mole Snacks: +1/-2
Re: How do I solve for these Alkene and Epoxide Chemistry problems? :(
« Reply #29 on: December 08, 2012, 05:18:38 PM »
Ok...these are my questions...


Sponsored Links