Chem 227, Fall 1997

Section 508

EXAM #2 - 100 pts

1. (3 pts) Draw the structure corresponding to the IUPAC name below.

(Z)-2-bromo-3,4-dimethyl-3-hexene


2. (4 pts) Rank the substituents below using Cahn-Ingold-Prelog sequence rules by numbering the highest priority substituent as 1 and the lowest priority group as 4.


3. (4 pts) Chloramphenicol is an antibacterial and antirikettsial compound with molecular formula C11H12Cl2N2O5. Calculate the number of rings plus double bonds (degrees of unsaturation) for chloramphenicol. Show your calculations.

C11H12Cl2N2O5 = C11H12Cl2N2 = C11H14N2 = C11H12

11 x 2 = 22 + 2 = 24 24 - 12 = 12 12/2 = 6 degrees of unsaturation

4. (27 pts) Predict the major products for the following reactions. If more than one product is expected in significant amounts, draw all of them. Show stereochemistry where relevant.

a)

b)


c)

d)

e)

f)

g)

h)

5. (9 pts) Give reagents suitable for creating the following transformations. Write your answers over the arrows. If more than one set of reagents is required, be sure you indicate the separate sets of reagents.

a)

b)

c)


6. (6 pts) Provide the structure of the starting material necessary to complete the following transformations.

a)


b)

Consider the reaction below to answer Questions 7 - 10.

7. (4 pts) This reaction is an example of: (Circle as many as appropriate)

8. a) (4 pts) This reaction proceeds by the initial reaction of the alkene with HBr to give an intermediate. Show the mechanism for this reaction step by using arrows to show electron movement and drawing the structure of the initial intermediate.

b) (4 pts) Complete the reaction by drawing the mechanism for the transformation of A into B and then into the final product.

9. (2 pts) Species A above is: (Circle the correct answer)

10. (8 pts) Draw a qualitative reaction coordinate diagram for the reaction outlined in question 8. Fully label the diagram.

The diagram must have two high-energy intermediates. Reaction occurs readily an goes to completion: therefore exothermic.

Consider the reaction shown below.

11. (4 pts) Using Hammond's posulate, explain why the radical shown above is formed in this reaction instead of the radical shown below.

See page 208 of textbook. Hammond's postulate restateed: The transition state for an endothermic reaction step (forming a high energy intermediate) resembles the high energy product in structure and energy. Therefore the transition states (there are two different transition states to consider) leading to I or to II will resemble I and II in energy. Since I is lower in energy than II (tertiary radicals are more stable than secondary radicals), the transition state leading to I will be lower in energy than the transition state leading to II. This means that I will be formed faster than II (lower activiation energy).

12. (9 pts) Draw examples of three different classes of alkenes that would give the same alkane upon hydrogenation and rank the three alkenes in order of magnitude of heat of hydrogenation assigning 1 to the alkene with largest heat of hydrogenation and 3 to alkene with smallest heat of hydrogenation.

This question was taken from lecture notes on Chapter 6. See Section 6.7

13. (4 pts) Draw the reactive intermediate formed upon the reaction of 1-methylcyclohexene with Hg(OAc)2 as the electrophile:

See page 230.

14. (4 pts) Consider a one-step reaction in which the energy of activation is 50kJ/mol and for which the total bond energies of bonds broken is 950 kJ/mole and the total bond energies of bonds formed is 970 kJ/mol.

Draw a quantitative reaction coordinate diagram for this reaction on the graph below. Be sure to label the energy scale.



15. (4 pts) Explain the requirements for a single chemical to decompose by an explosion.

See pp. 171 - 172.



© Kenn Harding, Texas A&M University