Reaction mechanism for ketone and vinyl lithium

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Discussion Overview

The discussion revolves around the reaction mechanism of 1-bromo-3-propanone when treated with vinyl lithium. Participants explore the nature of the carbonyl's reactivity and the implications of the molecular structure in the context of organolithium reagents.

Discussion Character

  • Homework-related
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions the validity of 1-bromo-3-propanone as a molecule, suggesting that it cannot be a ketone due to propane's carbon count, which would lead to an aldehyde instead.
  • Another participant proposes that the intended molecule might be 1-bromo-2-propanone and shares their understanding of the reaction, noting that the vinyl lithium would add to the carbonyl.
  • A participant expresses confusion about how the organolithium reagent can attach to the sp2 hybridized carbonyl carbon, seeking clarification on the mechanism.
  • One response suggests treating the organolithium compound as R-Li+ and applying standard arrow-pushing techniques, while also advising consideration of the bromine's role in the reaction.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the correct structure of the starting material, with some asserting that 1-bromo-3-propanone is incorrect and others suggesting an alternative. The discussion reflects uncertainty regarding the mechanism of attachment of the organolithium reagent to the carbonyl.

Contextual Notes

There is ambiguity regarding the correct molecular structure and the implications of the carbonyl's hybridization state on the reaction mechanism. The discussion does not resolve these uncertainties.

brake4country
Messages
216
Reaction score
7

Homework Statement


What is the product of 1-bromo-3-propanone treated with vinyl lithium?

Homework Equations

The Attempt at a Solution


I know that the carbonyl is attcked by the organolithium but I am having a hard time understanding how it attaches to the carbonyl since it is sp2 hybridized. Any suggestions? Thanks!
 
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Something must be wrong. 1-bromo-3-propanone is not a real molecule: propane only has 3 carbons, so a carbonyl on the 3-carbon would make it an aldehyde, not a ketone. Can you draw out the structure of the molecule that you intended to say?
 
I believe my study manual meant 1-bromo-2-propanone. But, here is the reaction that I have determined so far, attached below. The answer only says that the vinyl lithium would add to the carbonyl. Thanks!
 
brake4country said:
But, here is the reaction that I have determined so far, attached below.
I don't see the attachment.

brake4country said:
I am having a hard time understanding how it attaches to the carbonyl since it is sp2 hybridized.
This shouldn't matter. Just treat the organolithium compound as approximately R-Li+, with R = vinyl, and just do the same type of arrow-pushing you'd do with, e.g., butyllithium.

The one caveat is to think about not just the carbonyl, but the bromine as well.
 

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