1. Dismiss Notice
  2. Guest, be sure to check out How To Get Into Dental School, our free downloadable PDF with step-by-step details for dental school applicants!
    Dismiss Notice
  3. Dismiss Notice
  4. Download free Tapatalk for iPhone or Tapatalk for Android for your phone and follow the SDN forums with push notifications.
    Dismiss Notice

Chads vs. Destroyer -- Acetal/Hemi-Acetal

Discussion in 'DAT Discussions' started by Teeths, Aug 7, 2011.

  1. Teeths

    2+ Year Member

    Joined:
    Apr 13, 2011
    Messages:
    559
    Likes Received:
    85
    Status:
    Pre-Dental
    So I'm trying to decide when a ketone forms the acetal/hemi-acetal forms


    From Chads videos I have notes that:

    Ketone + alcohol ----acid catalyzed---> hemi-ketal that converts to the ketal form

    Ketone + alcohol ----base catalyzed--> hemi-ketal


    From the roadmaps of Destroyer:

    Ketone + 2 equiv of alcohol ----acid catalyzed--> acetal

    Ketone + 1 equiv of alcohol ----acid catalyzed---> hemi-acetal



    Huh? lol. So does it depend on acid/base catalyzed or equivalents of reactant?
    Also, is there a difference between acetal and ketal?

    Thanks guys!:)
     
  2. Note: SDN Members do not see this ad.

  3. invictusx

    2+ Year Member

    Joined:
    Jan 5, 2011
    Messages:
    556
    Likes Received:
    1
    Status:
    Dental Student

    It definitely depends on acid/base catalyzation. Also, think about the equivalence. Look at the difference between hemi-acetal and acetal. Look at the number of oxygens in both.
     
  4. Teeths

    2+ Year Member

    Joined:
    Apr 13, 2011
    Messages:
    559
    Likes Received:
    85
    Status:
    Pre-Dental
    So is Destroyer roadmap wrong?

    It has a ketone + 1 eq alcohol (with H+) that yields a hemi-acetal. In Chad's videos he said they could tell you the number of equivalents but don't have to.
    So if it's based on acid/base catalyzation I would have made this the acetal since it has (H+) which doesn't that mean acid?

    I'm still confused. Both are acid catalyzed in Destroyer roadmaps (pg 114 in 2011 version) and yet one yields the hemi and the other yields acetal.

    ??
     
  5. oceanblue5841

    2+ Year Member

    Joined:
    Apr 5, 2010
    Messages:
    60
    Likes Received:
    1
    Status:
    Pre-Dental
    You're making this way to hard. Keep it simple, if you get a problem like that, and your not given "equivalents" go with what Chad says, if you ARE given equivalents, then do what destroyer does. Or if you're like me and need a way to reason this kind of problem then look at it this way.

    Chad's explanation....When ketones or aldehydes undergo nucleophilic addition the general pattern is that, the nucleophile adds and the carbonyl oxygen is protonated forming a hydroxyl group. IF acid is present then the hydroxyl group can be protonated, forming water which is a good leaving group, and therfore another nucleophile can come and displace water, forming the ketal or acetal. IN base this doesn't happen because the OH is not protonated, you just get the hemiketal or hemiacetal form.

    Now lets say we run into a similar problem, and we see its acid catalyzed with only "1 equivalent" of the nucleophile. THERE is only ONE nucleophile, thats the only one that can add to the ketone or aldehyde, forming the hemiketal or hemiacetal. After that adds, there are no nucleophiles left to add, even if the reaction is acid catalyzed.

    This is how I reason it, it makes sense to me. I hope that helps a little.
     
  6. Teeths

    2+ Year Member

    Joined:
    Apr 13, 2011
    Messages:
    559
    Likes Received:
    85
    Status:
    Pre-Dental

    Alright, thanks a lot! I'm thinking the DAT won't be that finicky on this anyhow.
     
  7. fujindesu

    2+ Year Member

    Joined:
    Aug 8, 2010
    Messages:
    195
    Likes Received:
    0
    Status:
    Pre-Dental
    acid = "acid"tal
     

Share This Page