EXAM 1 - Chem 227 - Spring 1998

1. (4 pts)

• How many primary (1^o) carbons are in the above structure?
• How many secondary (2^o) carbons are in the above structure?
• How many tertiary (3^o) carbons are in the above structure?
• How many quaternary carbons are in the above structure?

2. (4 pts) The unusual compound below was reported in the chemical literature recently. Predict the hybridization of each of the atoms marked with an arrow in the structure.

3. (4 pts) Predict the bond angles for the atoms attached to the indicated atoms in the structure above.

4. (6 pts) There are three other significant resonance forms for the structure shown below. Draw them in the boxes provided. (Hint: one structure does not have octets around all atoms) BE SURE TO SHOW ALL FORMAL CHARGE and all non-bonded electron pairs.

5. (6 pts) Each of the followng Bronsted acid/base reactions is an equilibrium that lies to the right-hand side of the equation as indicated by the arrows.

a) Which three molecules are behaving as Bronsted bases in these equations? Write their formulas below.

b) List the formulas of the three molecules behaving as Bronsted acids in the order of decreasing acid strength.

6. (6 pts) Below is the structure of codeine, a derivative of morphine used in prescription cough medicines. Circle and name three different functional groups in codeine.

7. (6 pts) The molecule shown below is the product that results from the combination of three uncharged molecules that undergo two separate Lewis acid/Lewis base reactions. Draw the structures of the three reactants in the boxes provided.

8. (4 pts) Draw correct structures corresponding to the following names.

a) 3-ethyl-2,2,5,5-tetramethylhexane

b) cis-1-chloro-3-methylcyclopentane

9. (21 pts) The reactions shown below (J. Org. Chem. 1992 57, 2517-2518) gives the isomeric products shown. (Don't worry about the chemistry of this reaction.)

Conformational analysis can be used to predict the major product of this reaction!

a) (6 pts) Draw clear representations for the two chair conformations for compound A that are in equilibrium.

b) (3 pts) Of the above two conformations, circle the one expected to be more stable (lower strain energy).

c) (6 pts) Draw clear representations for the two chair conformations for compound B that are in equilibrium.

d) (3 pts) For the above two conformations, circle the one expected to more stable.

e) (3 pts) Which of the four boxes above contains the isomeric structure expected to be the most stable of the four? Write the box # here

10. (10 pts) Draw Newman projections showing the three possible staggered conformations for 2-chlorobutane using the C2-C3 bond for the Newman projection.

a) Draw the conformations sequentially with the indicated bond rotations. Rotate only the front carbon..

b) Circle the lowest energy conformation.

c) Draw a Newman projection representing the highest energy conformation for this molecule.

11. (2 pts) Convert the Newman projection below to a skeletal structure representation (no stereochemistry indicated).

12. (4 pts)

a) Draw a circle around the compouund(s) in which ionic bonds are expected.

NH₄Br

NH₂Br

NaOCH₃

BBr₃

b) Draw a circle around the compound(s) in which there are polar bonds but no permanent dipole.

CHCl₃

CCl₄

CBr₂Cl₂

NF₃

13. (8 pts) Acetonitrile, a common solvent, is observed to react with Lewis acids such as boron trifluoride as shown below.

14. (8 pts) Use the pK_a table at the end of this exam to answer this question. Nicotine exists as its conjugate acid at physiological pH, the pH of body fluids, which is about 7.

a) Give the approximate pK_a of the conjugate acid of nicotine.

b) Complete the equation below by drawing the products of the reaction and putting in the equilibrium arrows to show whether starting materials or products are favored.

15. (5 pts) Draw all structural isomers with formula C₃H₆BrCl.

16. (2 pts) Carbodiimide is one of the CH₂N₂ isomers with HNCNH connectivity and no formal charge. Draw a Lewis or line-bond structure for carbodiimide. Show all non-bonding electrons.