REVIEW QUESTIONS for Unit Test #2
 10. (8 pts) Draw Newman projections showing the three possible staggered conformations for 2,3-dimethylbutane using the bond highlighted in the structure below for analysis. Draw the conformations sequentially with the indicated bond rotations. Rotate only the front carbon. Circle the lowest energy conformation.  
 
 
 

11.(6 pts)
a) Draw both chair conformations for cis-1-methyl-4-ethylcyclohexane on the chair templates shown below.
 
 
 
 


 
 

a) Which structure would be predicted to have less strain energy?
12. (2 pts) Draw all axial bonds on the cyclohexane template shown below.
 
 


 

13. (4 pts) Convert the Newman projection below to a wedge-dash representation (stereochemistry must be shown) and to a skeletal structure representation (no stereochemistry indicated).

 

14. (6 pts) For each pair of molecules below, circle the more stable structure.
a)

b)


 
 
 
 

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.


 
 

 10. (8 pts) Draw a Newman projections showing the six possible conformations for the structure below using the C1-C2 bond for analysis. Draw the conformations sequentially with the indicated bond rotations. Rotate only the front carbon. Circle the highest energy staggeredconformation.  

11. (6 pts) Draw in all equatorial C-H bonds on the cyclohexane chair shown below.
 
 


 
 

12. (8 pts)
a) Complete the drawings below to show the two chair conformations for trans-1,3-dimethylcyclohexane.
 


 
 

    a) Which structure is more stable?
13. (4 pts) Convert the Newman projection below to a wedge-dash representation.


 

13. (8 pts) Consider the reaction coordinate diagram below.

        a) Is the reaction endothermic or exothermic?

        b) Is the Keq > or < 1?

        c) Are starting materials or products expected to predominate at equilibrium?

        d) If the activation for the reaction was not known, what minimum value could we place on the activation energy?


 
 

10. (6 pts) Consider the conformations of 2-methylbutane shown below to answer the following questions. a) Which of the structures has two gauche interactions?

b) Which of the structures represents the most stable conformation of 2-methylbutane?

c) Which of the structures represents the least stable conformation of 2-methylbutane?
 
 

 15. (4 pts) Consider the structures below.

a) Which hydrocarbon(s) above has/have only primary and secondary hydrogens?
    b) Which hydrocarbon(s) above has/have primary, secondary, and tertiary hydrogens?


1. Consider the reaction below to answer the following questions:

a) (2 pts) This reaction is an example of: (Circle the letter of your response.)

A. a substitution reaction.
B. a rearrangement reaction.
C. an addition reaction.
D. an elimination reaction.

b) (2 pts) The first step of this reaction is shown below. Draw curvey arrows showing the electron flow in this step.

c) (2 pts) Species Q, above, is: (Circle the letter of your response.)
A. a transition state.
B. an intermediate.
C. a radical cation.
D. a carbene.

d) (4 pts)The second and third steps of this reaction are shown below. Identify the nucleophile and the electrophile in the third step. Write the terms in the blanks below the molecules.   e) (3 pts) Describe the hybridization and geometry of the oxygen bearing the positive charge in species R above.  
 
 
 
  f) (5 pts) Using the following bond dissociation energies, calculate the estimated deltaHo for this reaction. Show your calculations for full credit. Bond D kJ/mol

3o C-OH 380

3o C-Br 263

2o C-Br 274

1o C-OH 380

H-OH 498

H-Br 366

deltaHo =

Is this reaction endothermic or exothermic?
 

 g) (6 pts) Draw a qualitative reaction energy diagram for this three-step reaction. The first step of this reaction is the slow step. Fully label the diagram, including the coordinates.