Why is an alcohol more reactive than a ketone?

Discussion in 'MCAT Study Question Q&A' started by Deepa100, Jun 15, 2008.

  1. Deepa100

    Deepa100 Junior Member

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    Is it because alcohol has a proton it can lose? Also, why is alcohol more polar than a ketone?
     
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  3. 161927

    161927 Guest

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    An alcohol is more polar than a ketone because it can engage in hydrogen bonding with more molecules of itself or with polar solvents. A ketone can hydrogen bond with other polar molecules with acidic hydrogens, but it cannot hydrogen bond with itself.

    Alcohols have a different type of reactivity than ketones, and I'm not certain what you mean when you say that alcohols are more reactive. Ketones tend to react by nucleophilic addition/elimination reactions, while alcohols exhibit other kinds of chemistry, such as eliminations and substitutions.
     
  4. unsung

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    Also, I believe the carbonyl bond is shorter (pi bond) than the C-O bond in alcohol, so the dipole moment would be smaller too, since it's a function of length.
     
  5. Deepa100

    Deepa100 Junior Member

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    I have seen a line in a AAMC test solution somewhere that stated that alcohols are more reactive. I forgot the context though, I will have to go back and look.
     
  6. niranjan162

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    #5 niranjan162, Jun 16, 2008
    Last edited: Jun 17, 2008
  7. JA Prufrock

    JA Prufrock Serenity Now!

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    I don't think that's right; oxygen has 2 lone pairs on both the hydroxyl group and the carbonyl group
     
  8. seraph524

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    Alcohols are more reactive because the -OH can be made into a great leaving group via protonation. Turning a R-OH into R-OH2+ makes the R more susceptible to nucleophilic attack.

    Example:

    R-OH + HBr --> R-OH2+ + Br- --> R-Br + H2O

    This can be done with HI and HCl (to a lesser degree) as well.

    Ketones however, even when protonated, is not a leaving group. A protonated ketone will only allow the carbonyl carbon to be susceptible to nucleophilic attack, turning it into an alcohol.
     
  9. seraph524

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    Note however, these are just general rules. A complex tertiary alcohol will be LESS reactive than a simple acetone.
     
  10. Deepa100

    Deepa100 Junior Member

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    Thanks, man!
     

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