Pima County Community College

OCHEM 1

Chapter 6—An Overview of Organic Reactions

SHORT ANSWER

Exhibit 6-1

Classify each reaction below as a(n):

addition elimination substitution rearrangement

Place the letter corresponding to the correct answer in the blank to the left of the reaction.

1)              

2.              

3.              

Exhibit 6-2

Identify the functional groups present in each compound below and predict the direction of polarity in each.

4.      mustard gas Cl-CH₂CH₂-S-CH₂CH₂-Cl

5.

Exhibit 6-3

Classify each structure below as a nucleophile or electrophile and briefly explain your choice.

6.

7.

8.

Exhibit 6-4

Identify the nucleophile and electrophile in each reaction below and label them.

9.     

10.

11.

Exhibit 6-5

Add curved arrows to the following reactions to indicate the flow of electrons in each.

12.   

13.   

14.   

15. Acidic ether cleavages are typical substitution reactions. Use the information in Table 6.3 of the textbook to calculate D H° for the reaction of ethyl methyl ether with hydrogen chloride and hydrogen iodide.

Which acid would you predict to be most effective at ether cleavage?

Exhibit 6-6

MATCH each definition to one of the terms below. Place the letter of the term in the blank to the left of the definition.

polarization                                                      substitution

addition reaction                                               nucleophile

homolytic bond breakage                                 radical reaction

electrophile                                                       elimination reaction

polar reaction                                                   heterolytic bond breakage

16.           A process involving symmetrical bond breaking and bond making.

17.           This occurs when both bonding electrons remain with one product fragment.

18.           A reaction where two reactants exchange parts to give two new products.

19.           A general term for species which have electron rich sites that can form a bond by donating a pair of electrons to an electron poor site.

Exhibit 6-7

Consider this reaction when answering the following question(s):

20.    Refer to Exhibit 6-7. This reaction is an example of: a substitution reaction.

a rearrangement reaction. an addition reaction.

an elimination reaction.

21. Refer to Exhibit 6-7.

The structures below show the step-wise bond making and bond breaking in this reaction.

Draw curved arrows to show the electron flow that has occurred in each step.

Calculate K_eq for the reaction in part a. Calculate D G° for the reaction in part a.

22. The original question has been combined with #21 as part b. This placeholder question is here to maintain the integrity of the numbering system between the printed copy and ExamView. Therefore, it has been marked "do not use on test" in ExamView's question information dialog. As a result, this placeholder question is automatically prevented from being chosen as a test question.

23. Refer to Exhibit 6-7. Draw a qualitative energy diagram for the reaction (assume that the first step is slower than the second step). Label fully.

Exhibit 6-8

MATCH each definition to one of the terms below. Place the letter corresponding to the term in the blank to the left of the definition.

transition state                                                  standard Gibbs free energy change

endergonic reaction                                          exergonic reaction

activation energy                                              reaction intermediate

24.           A species that lies at an energy minimum between steps on a reaction.

25.           The energy needed by reactants to reach the transition state.

26.           A reaction where D G° is negative.

27.           D G° = -RT ln K_eq

Exhibit 6-9

Use the reaction energy diagram below to answer the following question(s).

28.    Refer to Exhibit 6-9. The reaction depicted in this reaction energy diagram can best be described as: a slow exothermic reaction

a fast exothermic reaction

a slow endothermic reaction a fast endothermic reaction

29. Refer to Exhibit 6-9. The transition state is found at point      on the diagram.

30. Refer to Exhibit 6-9. The products are found at point      on the diagram.

31. Refer to Exhibit 6-9. The free-energy change for the reaction is indicated at point   on the diagram.

32. Refer to Exhibit 6-9. The reactants are found at point      on the diagram.

Exhibit 6-10

Consider the reaction of 2-bromo-2-methylpropane with water, shown below, to answer the following question(s).

Diagram 1: The first step of this reaction is shown below.

Diagram 2: The second and third steps of the reaction are shown below.

33.    Refer to Exhibit 6-10. This reaction is an example of: a substitution reaction.

a rearrangement reaction. an elimination reaction. an addition reaction.

34.    Refer to Exhibit 6-10. In Diagram 1, Species B is: a carbene

a carbanion

a carbocation a radical

35. Refer to Exhibit 6-10. In Diagram 1, add curved arrows to indicate electron flow.

36. Refer to Exhibit 6-10. In Diagram 2, label the nucleophile, Nu, and the electrophile, E⁺, in the blanks provided under the structures.

37. Refer to Exhibit 6-10. In Diagram 2, draw arrows on the structures showing electron flow.

38.    Refer to Exhibit 6-10. The reaction in Diagram 2 is an example of: a pericyclic reaction.

a radical reaction.

a concerted reaction. a stepwise reaction.

39. Refer to Exhibit 6-10. Using the bond dissociations values in the table below, calculate the D H° for the reaction in Diagram 2. Show your calculations for full credit.

H-Br                                                               366

40. Refer to Exhibit 6-10. Based on all of the data presented in Exhibit 6-10, draw a qualitative reaction energy diagram for the reaction of 2-bromo-2-methylpropane with water. The first step is the slowest step of the reaction. Fully label the diagram, including the coordinates.

Exhibit 6-11

In each reaction below:

Label the nucleophile (Nu) and the electrophile (E).

Draw arrows on the structures showing electron flow in the reaction.

43. The following represents the carbocation intermediate in the reaction of an alkene with HBr.

Draw the skeletal structure of the possible products and reactants.

44. What are the major differences between a reaction occurring in flask in the laboratory compared to a reaction occurring in a biological system?

45. The alkane formed by hydrogenation of (S)-4-methyl-1-hexene is optically active while the one formed by hydrogenation of (S)-3-methyl-1-pentene is not. Explain.

46. Compound A, C₉H₁₆, was found to be optically active. On catalytic reduction over a palladium catalyst, 2 equivalents of hydrogen were absorbed to yield compound B. Ozonolysis of A gave two compounds. One was identified as acetaldehyde, CH₃CHO. The other compound, C, was an optically active dialdehyde, C₅H₈O₂. Formulate the reactions and draw structures for compounds A, B and C.

47. The enzyme aconitase catalyzes the hydration of the alkene functional group of aconitic acid to give two products, citric acid and isocitric acid. Isocitric acid is optically active; citric acid is not optically active. Based on your knowledge of alkene hydration and optical activity, the structure of citric acid is:

cannot be determined

MULTIPLE CHOICE

1.    Which of the following could act as an electrophile? CN^–   NH₃

2.    Which of the following could act as a nucleophile? HCl   BF₃

CH₃NH₂                                                         CH₃Br

3. Consider the following grayscale electrostatic potential map. The regions are labeled as to color.

Which atom is the most electron poor?

1                                                                     3

2                                                                     4

H

4. Consider the following grayscale electrostatic potential map. The regions are labeled as to color.

Which atom is the most likely to be attacked by a nucleophile?

1                                                                     3

2                                                                     4

5. In a polar reaction mechanism, the atom that gives away electrons in a neutral nucleophile will end up as a(n):

cation                                                             radical

anion                                                              neutral molecule

6. Consider the following.

This process would result in the formation of: a positive ion and negative ion.

two neutral species. two radicals.

two negative ions.

a positive ion and a neutral species. a negative ion and a neutral species.

7. Consider the following process.

Which of the following correctly applies?

termination step                                              polar reaction

unsymmetrical bond formation                      produces a radical ANS: A

8.    A reaction that establishes equilibrium with almost no reactants present:

is exergonic.

has a negative DG°.

 has a large Keq.

all of the above.

9. A reaction has D H° = –14.7 kJ and D S° of 35.7 J/(K • mol), will

be exergonic.                                                  have a very small K_eq.

have a positive D G°.                                      will proceed rapidly.

10. Which of the following compounds would produce a single product when treated with Cl₂ in the presence of ultraviolet radiation?

butane

2-methylpropane

2,2,-dimethylpropane

All would produce multiple products.

11. Consider a reaction with the following thermodynamic properties.

D H° = 77.7 kJ

D S° = –35.7 J/(K • mol)

D G°= 88.4 kJ

This reaction:

will be spontaneous at low temperatures.

has bonds in the products that are weaker than the reactants. may have fewer and more complicated molecules in the product. will proceed very slowly.

12. Consider the following energy diagram for an enzyme-catalyzed reaction.

How many transition states are involved?

2                                                                     4

3                                                                     5

13. Consider the following energy diagram.

Which step has the least endergonic D G^±?

A - C                                                              E - G

C - E                                                               G - I