Questions dealing with electrophilic addition reactions

  1. In carbon tetrachloride solution, bromine adds to (E)-3-hexene to yield the meso 3,4-dibromohexane isomer. Write a mechanism which explains this behavior.

    Meso

    Try opening the other way and forming also the other bromonium ion.

  2. Myrcene, A, a fragrant component found in bayberry wax, has the formula C10H16 and is known not to contain any triple bond. On catalytic hydrogenation, myrcene is converted to 2,6-dimethyloctane, B, a compound of formula C10H22. Ozonolysis of A followed by treatment with zinc and water yields 2 mol of formaldehyde, HCHO, 1 mol of acetone (CH3COCH3) and a third compound, C, with formula C5H6O3.
    1. How many units of unsaturation are present in myrcene?

      C10H16 compared to C10H22 indicates three such units 

    2. What is the structure of myrcene, compound A?

  3. At the beginning of the biogenesis of squalene isopentenyl pyrophosphate, CH2=C(CH3)CH2CH2OPP, is enzymatically isomerized to dimethylallyl pyrophosphate, (CH3)2C=CHCH2OPP. These two compounds then react together to yield geranyl pyrophosphate, (CH3)2C=CHCH2CH2(CH3)C=CHCH2OPP. Assuming that the weakly basic pyrophosphate anion is, like the protonated hydroxyl group, a good leaving group, R-OPP ® R+ + OPP- suggest a mechanism by which geranyl pyrophosphate might be formed.

  4. In methanol solution, bromine adds to ethene to yield not only 1,2-dibromoethane but also Br-CH2-CH2-O-CH3 . Write a mechanism which explains this behavior.

  5. An unknown hydrocarbon "A" with formula C6H12, reacts with 1 equivalent of H2 over a Pd catalyst. It also reacts with OsO4 to give diol "B". When oxidized with KMnO4 in acidic solution, "A" gives two fragments. One fragment is propanoic acid, CH3CH2CO2H, and the other is ketone "C".
    1. What is the structure of "A"?

      2-methyl-2-pentene

    2. Write a mechanism for the formation of "C".

    Look up mechanism of oxidation
  6. Compound "A", C10H18O, reacts with dilute H2SO4 at 250C to yield a mixture of two alkenes, C10H16. The major product, "B", gives cyclopentanone,

    as the sole product on ozonolysis.

    1. What is the structure of "A"?

    2. What is the structure of "B"?

  7. Propose a mechanism for the following reaction:

  8. Starting from 1-methylcyclohexene, propose a synthesis for each of the following:
    1. 1-methylcyclohexanol

      2. 1. Hg(OAc)2/THF/H2O 2. NaBH4
    2. 2-methylcyclohexanol

      3. 1. B2H6 2. H2O2/OH-

    3. 1-bromo-1-methylcyclohexane

      4. HBr/absence of peroxides
    4. 1-bromo-2-methylcyclohexane

      5. HBr/presence of peroxides

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This page is maintained by Dr. Ed Blackburn (Ed.Blackburn@UAlberta.CA), course instructor.

Updated July 24, 2001