CHE 230-001 – Organic Chemistry

Exam 1, September 27, 2006

Name ________________________________ Student ID Number ________________

Before you begin this exam: First: Note the blank page at the end provided for scrap paper. It must be returned at the end of the exam. Second: Place your student identification on your desk. A proctor will come around to check everyone’s ID. Third: Read through the entire exam. Do not waste time on problems that you can’t do if there are others that look easy. Fourth: It is critically important that your answers be written in a clear, unambiguous manner. Answers in which your intentions are unclear will not receive credit. Fifth: Read the instructions for each problem. You will have until 8:50 a.m. to complete this exam. There will be no extensions, so budget your time carefully.

Problem Points Score

1. 6 _____

2a. 8 _____

2b. 5 _____

2c. 8 _____

3. 12 _____

4. 5 _____

5. 6 _____

6. 8 _____

7. 10 _____

8. 9 _____

9 6 _____

10. 6 _____

11. 6 _____

12. 5 _____

Total 100 _______

1. (6) Using Newman projections, draw a non-eclipsed (staggered) conformation of 2,3-dimethylbutane that is not the most stable (i.e. the next most stable conformation).

2. (8+6+8=22) Consider the linear molecule, acetonitrile N-oxide, CH₃CNO.

(a) Draw a Lewis structure for the most stable resonance form for this molecule. Show lone pairs and formal charges.

The three lone pairs on the O may not show up here.

Partial credit: +2 for correct no. of electrons

+2 for octets on all atoms except H

+2 for correct charges

+2 for most stable resonance form

(b) Draw the next most stable alternate resonance form.

The two lone pairs on the O and the one lone pair on the C may not show up here.

Partial credit: +2 for correct number of electrons

+2 for correct charges

+2 for octets on all atoms except H

(c) Assign hybridization to the four hybridized atoms in this neutral molecule by writing the appropriate abbreviation, sp³, etc., below each atom below.

C ──── C ───── N ───── O

_sp³_ _sp__ _sp_ __sp²_

Partial credit: +2 for each assignment that is in accord with the rules for the two structures shown in parts a and b.

3. (a) (3) How many degrees of unsaturation does C₄H₄O have? __three_____

(b) (9) Draw three structural isomers of C₄H₄O . None may have formal charges. All must obey the octet rule.

There are many more correct answers. As long as there are no formal charges, octets around all atoms, and three degrees of unsaturation.

4. (5) Assume that the heats of formation of A-D below are all negative. Circle the alkene below with the most negative heat of formation.

C is most highly substituted alkene and therefore the most stable and the one with the most negative heat of formation.

|_____________|

5. (6) How many ¹³C NMR signals are expected for each of the molecules below. Write that number on the line below each structure.

_Two____ __Two___

6. (8) Circle all the chiral molecules among those shown below. First, second and third structures below. All the others have a plane of symmetry and are achiral.

|____________________________|

7. (10) Using asterisks identify all the stereogenic sp³ hybridized atoms in the molecule below.

8. (9) Four terms of stereochemical relationship are listed below. They are followed by three pairs of molecules. For each pair of molecules choose the term that describes the relationship shown in that pair. Write the appropriate capital letter on the line under the pair of molecules.

A. enantiomers (configurational)

B. diastereomers (configurational)

C. structural (or skeletal) isomers

D. identical

E. not isomers

(a) (b)

____D. identical__ ___B. diastereomers

(c)

__C. structural isomers___

9. (6) In the underlined spaces provided in the name, add the correct stereochemical labels (R, S, E, or Z) to the name of the molecule shown below.

(2_S_,4_S_)-2,4-dichlorohexane

10. (6) Write the major organic product formed in the reaction below.

11. (6) Draw the structure of an alkene that could be used to form the molecule below.

12. (5) Draw an orbital picture for ketene, CH₂CO . The connectivity order is C-C-O. Show the correct geometry with solid lines for hybrid orbitals in the plane, wedges for hybrid orbitals coming out from the plane, and dashed lines for hybrid orbitals extending behind the plane of the paper. Show p orbitals by drawing the top and bottom lobes for each.

The left carbon has one vertical p orbital. The middle carbon has two mutually perpendicular p orbitals, one parallel to the left p orbital and the other parallel to the right p orbital on oxygen. The oxygen has a p orbital parallel to one of the middle p orbitals and perpendicular to the p orbital on the end carbon. The two ends of the molecule are in planes that are perpendicular. The end carbon is sp² hybridized, the middle carbon is sp hybridized and the oxygen is sp² hybridized.