Allyl Bromide + HBr - Compounds formed during reaction.

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Discussion Overview

The discussion revolves around the reaction of allyl bromide with HBr, specifically focusing on the possible products formed during the electrophilic addition process. Participants explore various mechanisms and intermediates that could lead to different products, including major and minor outcomes.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant proposes that the electrophile attacks first, leading to a specific intermediate and product formation.
  • Another participant suggests that the reaction primarily follows Markovnikov's rule, but acknowledges the presence of Anti-Markovnikov products in low yield.
  • A participant challenges the omission of an intermediate step in the proposed mechanism, asserting that their interpretation includes a necessary shift of the pi bond.
  • Some participants argue against the feasibility of the proposed intermediate, stating that the mechanism does not allow for the separation of charges as suggested.
  • One participant emphasizes the importance of considering conjugation in allyl bromide and suggests that resonance may play a role in the reaction mechanism.
  • Another participant defends their method of showing the electron cloud shift as a means to facilitate the formation of the major product.

Areas of Agreement / Disagreement

Participants exhibit disagreement regarding the proposed mechanisms and the validity of certain intermediates. There is no consensus on the exact pathway of the reaction or the nature of the products formed.

Contextual Notes

Participants reference various mechanisms and textbooks, indicating that there may be differing interpretations of the reaction process. The discussion highlights the complexity of electrophilic addition and the potential for multiple products, but does not resolve the uncertainties surrounding the mechanisms involved.

AGNuke
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Allyl Bromide, during the addition of HBr gives

CH_3-CHBr-CH_2Br
CH_2Br-CH_2-CH_2Br
CH_3-CH_2-CHBr_2
CH_3-CBr_2-CH_3

My take
During the addition of HBr, electrophile will attack first, considering the shift of pi bond in allyl bromide as follows:

BrCH_2-CH=CH_2 \longrightarrow BrCH_2-\overset{+}{C}H-\overset{-}{C}H_2

H+ will attack on negative C. Now, to add Br- on positive one, I get the first option.

But the question is asking all possible products, it seems (possible intermediates/minor products). So, the possibilities of forming the other products is not theoretical impossible, I suppose.

All I need is the mechanism, which can lead to the formation of other products. I am currently working on some mechanisms.
 
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This question is based on the electrophilic addition to alkenes.

AGNuke said:
BrCH_2-CH=CH_2 \longrightarrow BrCH_2-\overset{+}{C}H-\overset{-}{C}H_2

The reaction doesn't really proceed like this. Check the following link for the mechanism: http://www.chemguide.co.uk/mechanisms/eladd/symhbr.html#top
It's obvious that the chief product is formed through Markovnikov addition but there is still a low yield of the Anti-Markovnikov product.
 
The mechanism mentioned there omitted the intermediate step I mentioned.

BrCH_2-CH=CH_2 \longrightarrow BrCH_2-\overset{+}{C}H-\overset{-}{C}H_2\xrightarrow[]{+H^+}BrCH_2-\overset{+}CH-CH_3

And I know there can be other potential minor products, that's why I asked the question.
 
AGNuke said:
The mechanism mentioned there omitted the intermediate step I mentioned.

BrCH_2-CH=CH_2 \longrightarrow BrCH_2-\overset{+}{C}H-\overset{-}{C}H_2\xrightarrow[]{+H^+}BrCH_2-\overset{+}CH-CH_3

And I know there can be other potential minor products, that's why I asked the question.

There's nothing omitted, the intermediate you mention doesn't form (at least in electrophilic addition). You can't break the pi-bond and then add H+. Refer a good book.
 
Who's breaking pi bond? I am only shifting it. Check the arrows in the link.

Moreover, here's an excerpt from Morrison and Boyd

book said:
To form the bond with hydrogen, carbon uses the \pi electrons formerly shared by other C atom. This leaves the other C atom with only sextet of electrons...

There's only one way to show the intermediate process, to shift the pi electrons.
 
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Note that you can't go about shifting pi electron clouds the way you did, and leave separated charges uncompensated for, and you definitely can't have something like that as the first step of a reaction mechanism.

I suggest you consider conjugation in allyl bromide.
Bromide has a lone pair of electrons it can donate, and the pi electron cloud can shift. Try using both of these facts to get a structure that would be in resonance with the structure of allyl bromide given.
 
I only showed the cloud shift under the influence of the electrophile, I just show them, it makes it easier to make major product.
 

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