1. Hey Guest! Check out the 3 MCAT Study Plan Options listed in the 'stickies' area at the top of the forums (BoomBoom, SN2ed, and MCATJelly). Let us know which you like best.

    Also, we now offer a MCAT Test-Prep Exhibitions Forum where you can ask questions directly from the test-prep services.
    Dismiss Notice
  2. Dismiss Notice
  3. Download free Tapatalk for iPhone or Tapatalk for Android for your phone and follow the SDN forums with push notifications.
    Dismiss Notice
  4. Hey Texans—join us for a DFW meetup! Click here to learn more.
    Dismiss Notice
Dismiss Notice

Interview Feedback: Visit Interview Feedback to view and submit interview information.

Interviewing Masterclass: Free masterclass on interviewing from SDN and Medical College of Georgia

organic chem problem---

Discussion in 'MCAT Discussions' started by Steve19, Dec 5, 2005.

  1. Steve19

    Steve19 Member
    5+ Year Member

    Joined:
    Sep 9, 2005
    Messages:
    51
    Likes Received:
    0
    Status:
    Pre-Dental
    I need help in some questions in org chem....any 1 have time to help me?
    :p :rolleyes:

    Reaction of R-2-butanol with chromic acid (H2CrO4) and then with NaBH4
    produces what product(s). What stereochemistry does(do) the product(s)
    have(has)? Is it optically active? Fully explain your answer.

    I still got more questions --can I post them in this forum ? !
    thanx
     
  2. Note: SDN Members do not see this ad.

  3. Nikki2002

    Moderator Emeritus 7+ Year Member

    Joined:
    Jun 16, 2005
    Messages:
    13,152
    Likes Received:
    2
    Status:
    Medical Student
    the chromic acid will turn the alcohol into a carboxylic acid, thereby removing the stereochemistry. Now, you have to determine if sodium borohydride is strong enough to reduce the carboxylic acid back to an alcohol.
     
  4. PittMedicine

    PittMedicine Membership Revoked
    Removed

    Joined:
    Nov 4, 2005
    Messages:
    201
    Likes Received:
    0
    Status:
    Pre-Medical
    its not, only LiAlH4 is...read a book
     
  5. Steve19

    Steve19 Member
    5+ Year Member

    Joined:
    Sep 9, 2005
    Messages:
    51
    Likes Received:
    0
    Status:
    Pre-Dental
    any 1.......plz help!
    1) How can you account for the fact that glucose reacts with the Tollens reagent
    to give a silver mirror, but glucose "-methyl glucoside does not?

    2) Reaction of R-2-butanol with chromic acid (H2CrO4) and then with NaBH4
    produces what product(s). What stereochemistry does(do) the product(s)
    have(has)? Is it optically active? Fully explain your answer.

    3) Two compounds with the same molecular formula have entirely different
    boiling points. One of these compounds, ethanol (CH3CH2OH) has a boiling
    point of 78.5 °C. The other compound, dimethyl ether (CH3OCH3) has a
    much lower boiling point (i.e., !25 °C). Fully explain this.

    4) Treatment of bromoacetone with ammonia yields a compound having the
    formula C6H10N2 rather than the expected 1-amino-2-propanone. What is a
    likely structure for the product and how do you explain the reaction?

    5) Glycogen, the storage form of glucose in animals; whereas, starch is the storage
    form of glucose in various plants. With genetic information being so similar in
    all life forms on this planet, why would there be these two different storage
    forms of glucose in plants and animals?

    6) Cellulose is a polymer of $-linked D-glucose units. Do you think there would
    be an effect on the structure of cellulose if there were alternating L- and Dglucose
    units instead of just D-glucose units? Fully explain your answer.

    7) Histidine is an aromatic amino acid even though it has a total of 8 B electrons.
    Is this reasonable? Fully explain your answer.

    8) The amino acid arginine is the most basic amino acid found in proteins. It has
    a guanidino group (shown in red below), which contributes to its basicity, and
    the over all structure is shown below:
    2
    H2N!C!NH!CH2CH2CH2CH!C!O!H
    2 * 2
    NH NH2 O
    Lysine is another basic amino acid and its ,-amino group, shown in red below)
    contributes to its basicity.
    H2N!(CH2)4!CH!C!O!H
    * 2
    H2N O
    Arginine is much more basic than is lysine. How do you explain this?

    9) The polynucleic acids, DNA and RNA, are very similar to each other. The two
    differences are the reduction of the 2'-OH of the ribose moiety to produce the
    deoxyribose moiety and the use of thymine in DNA in place of uracil in the
    RNA. Explain why these two changes are important in the stability of DNA as
    compared to RNA.

    10) Cellular membranes are composed of various phosphatidic acids (i.e.,
    diacylglycerol phosphates with the acyl groups being long-chained, saturated,
    and unsaturated fatty acids). Explain why there must be unsaturated fatty
    acids in the phosphatidic acids? Naturally occurring unsaturated fatty acids all
    have the cis conformation.

    11) Gentiobiose, a rare disaccharide found in saffron and gentian, is a reducing sugar and
    forms only D-glucose on hydrolysis with aqueous acid. Reaction of gentiobiose with
    iodomethane and Ag2O yields an octamethyl derivative, which can be hydrolyzed
    with aqueous acid to give 1 equivalent of 2,3,4,6-tetra-O-methyl-D-glucopyranose and
    1 equivalent of 2,3,4,-tri-O-methyl-D-glucopyranose. If gentiobiose contains a $-
    glycoside link, what is its structure?
     
  6. Chromic acid oxidizes secondary alcohols like 2-butanol to the corresponding ketones. In this case, you would form 2-butanone. NaBH4 reduces the ketone back to the alcohol but you will lose stereochemical control of the reaction. Your final products include R-2-butanol and S-2-butanol in a 50:50 ratio. This racemic mixture is optically inactive.
     

Share This Page