CH 334      Fall 2002

Practice Questions for Exam 1

1.  Sildenafil is sold under the trade name Viagra and is approved for the treatment of impotence.  Complete the following tasks on the structure of Viagra.

1. Add all the lone pairs implied in this structure. shown above
2. What is the molecular formula of Viagra? C₂₂H₃₀N₆O₄S
 
3. Assign hybridization to the two oxygens attached to carbon atoms. Both are sp²
4. Is something wrong with sulfur in this structure? Explain.  Sulfur seems to be "breaking the octet rule" but it’s OK because S is a 3^rd period atom and has d orbitals in addition to the s and p orbitals, so it can have more than 8 electrons

2. Methyl vinyl ether has the Lewis structure shown below.  In the provided space, show the 3-D hybrid orbital bonding picture of methyl vinyl ether. (10 pts)

a) Indicate hybridization of the atoms

b)       Show overlap of orbitals to form bonds.

c)       Indicate the location of lone pairs.

** note that one of the lone pairs on oxygen is conjugated to the pi bond for resonance**

4) Rank the following in order of increasing pKa:

lowest pka        I     <         III     <       II       <       IV       <              highest pKa

5) Draw the structural isomers of the formula C₅H₁₀ with sp³ hybridized carbons only.

6. Show resonance forms for each of the following structures.  Use the arrow formalism to indicate electron movement from one resonance form to the next. 

7. For the molecule 2,5-dimethylhexane, give the anti and gauche staggered Newman projections for the C(3)-C(4) bond. 

8. Which one of the following IUPAC names is correct?

a)       2-ethyl-5-methylhexane                       c) 2,2,3-trimethylheptane

b)       2-methylcyclohexane                           d) 1,5-dichlorocyclohexane

9. Which of the following alkanes has the highest boiling point?

a)       2-methylpentane              c) 3,3-dimethylpentane                        e) 2-methylhexane

b)       heptane                              d) hexane

10. The following compound contains:

a)       two 1°carbons, seven 2° carbons, and two 3° carbons

b)       three 1° carbons, five 2° carbons, two 3° carbons, and two 4° carbons

c)       two 1° carbons, five 2° carbons, two 3° carbons and two 4° carbons

d)       seven 2° carbons, two 3° carbons, and two 4° carbons

11. a) Draw the two chair conformations of trans-1,4-dimethylcyclohexane.   

      b) Circle the structure which you expect to be the major conformation at equilibrium.