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Simple Organic Chem Question

Discussion in 'Pre-Medical - MD' started by DiverDoc, Nov 12, 2005.

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  1. DiverDoc

    DiverDoc KCUMB 2012
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    For an Sn1 mechanisim which will react faster?

    1. (CH3)3CCl +H20 > (CH3)3COH + HCl

    2. (CH3)3CBr +H20 > (CH3)3COH + HBr

    Both tertiary alkyl halides, but HBr is a stronger acid... So which forms at the faster rate and why?

    Thanks for any replies!
     
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  2. Dave_D

    Dave_D Senior Member
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    I ain't answering this one because it's just a leaving group question. Here's the page on wikipedia
    http://en.wikipedia.org/wiki/Leaving_group
    Once you understand that page it's pretty straight forward.
     
  3. Kitra101

    Kitra101 Senior Member
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    Havent done in a while, but pretty sure that the better leaving groups are those which are the weaker of bases and therefore the stronger of acids. A strong base leaving group, such as an OH or an NH2 would be harder to displace than a weaker base such as water or an iodide anion. When coming to the halogen group, the closer to fluorine, the weaker the acid, the stronger the base. I believe this is a function of atomic size with the smaller and more electronegative atoms being on the top right of the table with the larger, less electronegative atoms being on the bottom. I could be wrong, but if my memory serves me correctly, this may help.

    If so, the answer would be that HBr a stronger acid than HCl in that the Cl anion is a weaker base and a better leaving group than the Br anion. In case of the SN1, the better leaving group will promote more efficient movement in the reaction direction towards the intermediate tertiary carbocation to be attacked by a nucleophile. If there is not a stronger nucleophile than the displaced halogen, odds are that the halogen will attack the carbocation again and reform the original alkyl halide.
     
  4. masterMood

    masterMood Membership Revoked
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    If you find yourself running into trouble with assignments, please seek help from appropriate sources (professors, peer tutors, friends in class, etc.), not SDN; these forums are not to be used for homework help.

    Threads that are more general (e.g., "Can anyone give me helpful pointers for stereochemistry?") are fine, but threads that are posted with the intent of obtaining answers to specific homework, quizzes, tests, etc. will be closed.

    Good luck




    I predict the previous statements to be said by Psycho in the next 24 hours.
     
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  5. Flopotomist

    Flopotomist I love the Chicago USPS
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    You beat me to it Hermit.. although, i think it would be nice if a new forum were opened up for homework questions so people could come to SDN as a place to help each other out.
     
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  6. QofQuimica

    QofQuimica Seriously, dude, I think you're overreacting....
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    People do post HW questions sometimes in the MCAT Study Questions subforum. We will allow posters to do this as long as it doesn't get abused. If any of you have chemistry questions, I'll help you with them, but only after you try to answer them yourself first. I've already passed sophomore organic, so I'm not going to do your HW for you. ;) But if you've gotten stuck, I'll point you in the right direction.
     
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  7. Phil Anthropist

    Phil Anthropist SDN Moderator
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    Asking for homework help wasn't really an issue until recently. I even remember taking the time to answer a thread in pre-allo that asked about passive/active immunology. But lately a few users really started to abuse the forums by starting multiple threads that attempted to get other people to do their homework--and it was obvious that the people who posted these threads had put in very little effort. Unfortunately, allowing just a few homework help threads sets a precedent that could reduce the value of the forums. There may only be a few now, but with no regulation, there's a possibility that many others would follow. How useful would the pre-medical forums be if the forums were saturated with homework help threads?

    Another unfortunate problem is that cheating has become rampant in college. Graded assignments, online quizzes on services like WebCT, take-home examinations, etc., have all become commonplace in college curricula. There is no way for us at SDN to know for sure whether or not the apparent homework questions asked on these forums are legit. And SDN has no intent to encourage cheating.
    The idea of having a forum for homework questions has been discussed by the moderators on various occasions, but it doesn't look like it's going to happen. More people would go there to ask questions than to answer questions. In addition, there is no way to have a forum leader who could (1) take the role of answerman for an unlimited number of subjects/threads and (2) ensure quality control. It would be a little easier if the scope was limited to pre-medical sciences, but a lot of the same problems would still remain (even if it was an unmoderated, peer free-for-all).

    Q and Shrike's MCAT Sub-forum is something that a lot of people have taken advantage of and it's a great addition to SDN. That forum is different from a general homework help forum because (1) it's a subject/test-focused forum (2) it's run by users qualified to answer the questions and (3) the leaders explicitly state that inappropriate questions (e.g., actual questions from the AAMC or copyrighted practice tests) are not to be used and (4) quality control can be maintained.

    Sorry dIvErDoC, I've gotta close your thread. But hopefully you'll find the previous replies helpful.
     
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