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Biology/Chemistry: pH Level and Ionizable Groups

  1. Aug 28, 2007 #1
    1. The problem statement, all variables and given/known data

    Select any molecule [from the assigned chapter] that has more than 2 ionizable groups. Write its structures, showing every atom, at pH levels 1 and 7.

    2. Relevant equations

    See below.

    3. The attempt at a solution

    http://en.wikipedia.org/wiki/Geranyl_pyrophosphate

    The molecule that I chose is geranyl pyrophosphate:


    ____________________________________O_____O
    ____________________________________||____||
    CH3C(CH3)=CHCH2CH2C(CH3)=CHCH2--O—P--O--P--O-
    ____________________________________|_____|
    ____________________________________O-____O-

    This one does have 3 ionizable groups, right?

    At pH 1, the molecule is under acidic conditions, so will all the ionizable groups be protonated?

    ____________________________________O_____O
    ____________________________________||____||
    CH3C(CH3)=CHCH2CH2C(CH3)=CHCH2--O--P--O--P--OH
    ____________________________________|_____|
    ____________________________________OH____OH


    At pH = 7, the presence of water can be presumed(?), so does this arise?


    ____________________________________O
    ____________________________________||
    CH3C(CH3)=CHCH2CH2C(CH3)=CHCH2--O—P--OH
    ____________________________________|
    ____________________________________O-

    + __O
    ____||
    HO--P--O-
    ____|
    ____O-


    Thanks.
     
    Last edited: Aug 28, 2007
  2. jcsd
  3. Sep 1, 2007 #2
    Revision here.

    At pH 1, will all the groups be protonated like so?

    ____________________________________O_____O
    ____________________________________||____||
    CH3C(CH3)=CHCH2CH2C(CH3)=CHCH2--O--P--O--P--OH
    ____________________________________|_____|
    ____________________________________OH____OH


    At pH 7, will all the groups be unprotonated like so?

    ____________________________________O_____O
    ____________________________________||____||
    CH3C(CH3)=CHCH2CH2C(CH3)=CHCH2--O—P--O--P--O-
    ____________________________________|_____|
    ____________________________________O-____O-

    Or must I treat this like a triprotic acid in which each group is protonated at various instances? (If so, how do I go about doing this?)

    Thank you.
     
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