Anions SubSat-C-1

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Anions SubSat-C-1

Chemistry 212 Spring 2012

Substitution at Saturated Carbon-1

A. What is the Mechanism of the Following Reactions: See also CGWW CH 17 pp. 407-409

1. Reactions:

Group a

Reaction

Relative

Rate

(1.) CH 3 -Br + OH CH 3 -OH + Br 10 3

(2.) CH 3 CH 2 -Br + OH CH 3 CH 2 -OH + Br 30

H

H

(3.) CH 3 Br + OH CH 3 OH + Br 1

.

CH 3

CH 3

(1.)

(2.)

(3.)

Group c.

2. Developing and Testing Potential Reaction Mechanisms.

a. Formulating a Simple Model for the overall reaction to organize our discussions of potential mechanisms:

Consider groups a. -> c. of the kinetically controlled reactions above and use similarities in the overall reactions to create a simple model applicable

to all of the reactions.

(1.) Classify the reactions as addition, elimination or substitution. Provide your warrant.

(2.) What ar

e the similarities in the overall reactions among all of the groups of reactions

HO

HO

HO

O

+ CH 3 O S

+

+

CH 3

CH 3

O

O

O

O

S

O

CF 3

CH 3

CF 3

Reaction

(1.) CH 3 -I

(2.) CH 3 -I

(3.) CH 3 -I

Group b.

Reaction

Relative

O

Rate

CH 3 O

+

C CH 3

C CH3 + I 10 2

O

O

+ O CH 3

CH 3 O CH 3 + I 10 5

+

HO-CH 3

HO-CH 3

HO-CH 3

O

C

O

+

+

+

O

O

CF 3

O

S

O

O

S

O

CH 3

CF 3

O CF 3

Relative

Rate

10 4

10 6

1

CH 3 O

C

O

CF 3

+ I

1


Substitution at Saturated Carbon-1 2

(3.) Using the reaction aspects listed below, devise a simple general model that can represent all of the overall reactions. Produce a diagram of

your model below using symbols for the various aspects of the reactants and products (No mechanism (NO ARROWS) should be proposed

at this point). Provide a warrant for the construction of your model.

Aspects: The overall classification of the reaction, the site (atom) on the central organic molecule at which the reaction occurs and the

apparent function of the parts of the reactants based on structural changes from reactants to products.

b. Identification and Isolation of Reaction Variables:

(1.) WITHIN each reaction group (a. -> c.), what structural aspects of your simple model are IDENTICAL in all of the reactions Provide a

warrant that relates structures in each group to your simple model.

(2.) WITHIN each group (a. -> c.), what structural aspects of your simple model are CHANGING from reaction to reaction Provide a warrant

that relates structures in each group to your simple model.

(3.) How many structural aspects of your simple model are varied in each group Provide a warrant that relates structures in each group to your

simple model.

(4.) What effects do the structural changes identified in (2.) have on the reaction rate (Change or no change) Provide a warrant to support your

claim.


3 Substitution at Saturated Carbon-1

c. Use the approach from Kinetically Controlled Reaction-2 and the results of your analysis in section b. above to suggest characteristics

of the RATE DETERMINING (highest energy) ’s that could account for changes in reaction rates in each group of reactions (See b. (4.)).

(e.g. what do differences in energies determined from the rates suggest about the bonds that might be partially formed or broken and how the site

of HEE might have changed from the reactant to the ) Provide a warrant showing how the effects in b.(4.) allowed you determined these

structural differences

d. How many ways could the reaction occur Using only your simple model for these reactions developed in section 2. a. (3.) on p. 2 (not the

kinetic data), propose possible mechanisms (sequences of simple reaction steps) that might be possible for accomplishing the overall reaction

illustrated by your model.

e. Now consider what the ’s for each reaction step in your proposed mechanisms would look like and which structure best fits the characteristics

proposed in c. Can one structure account for all of the effects Provide a warrant showing how your claim is supported by your analysis in c.

f. Based upon e - energies and the previous reactions that you have studied, use your analyses and hypotheses from sections 2. a. - e. to formulate the

simplest reaction mechanism(s) (using arrows) that can account for all data in groups a -> c.


Substitution at Saturated Carbon-1 4

g. Review the process that is described in sections 2. a. -> f. above. In one or two sentences, describe how each step contributed to your final

understanding of how these reactions work. Could the steps have been done in a different order Did you have to add steps that were not explicitly

stated in this activity Briefly explain each response.

Step a. Formulating a Simple Model

Step b. Isolation of Reaction Variables

Step c. Suggest characteristics of the RATE DETERMINING (highest energy) ’s

Step d. Propose possible mechanisms

Step e. Fit proposed structure to characteristics from data.

Step f. Formulate the simplest reaction mechanism that fits the data.

B. In Class Application.

1,. Use the mechanism developed in Part A. to predict which reaction, (a.) or (b.), in each of the following pairs of reactions 1. -> 3. should proceed

at a higher rate. Provide a warrant using a reaction coordinate diagram to explain how your prediction was derived.

(a.)

(b.)

CH 3 O

CH O S

CH 3 O

+ O CH 3

O

CH 3 CH 2 O S

O

+ O CH 3

CH 3

CH 3

CH 3

CH O CH 3

CH 3 CH 2 O CH 3

CH 3

+

+

O

O

O

S

O

O

S

O

CH 3

CH 3

G

Rxn Coordinate


5 Substitution at Saturated Carbon-1

2. Analysis of the Application Process:

How was the analytical process used for the In Class Application related to that used in devising the reaction mechanism in Part A.2.a-g Provide

your warrant.

Reflector’s Report Discussion:

Identify the most important concepts you learned from this activity:

What questions remain

Strategy Analyst’s Report Discussion:

How did your group’s discussion of question 2.g on p. 4 help your group understand the process for determining a reaction mechanism from kinetic

data

How did your group’s discussion of, “4. Analysis of the Application Process”, above help your group in understanding the differences between the

process for devising a mechanism (inductive) and that for using the mechanism to predict relative rates (deductive)


Substitution at Saturated Carbon-1 6

Out of Class Applications

A. Reaction Rates:

Use the mechanism developed in Substitution at Saturated Carbon-1 to predict which reaction, (a.) or (b.), in each of the following pairs of reactions

should proceed at a higher rate and provide a warrant explaining how your prediction was derived.

1.

(a.)

O

O

CH 3 CH 2 O S CH 3 +

CH 3 CH 2 O

O

+

O

O

S

O

CH 3

(b.)

CH 3 CH 2

O

O

S

O

CF 3

+

O

CH 3 CH 2

O

+

O

O

S

O

CF 3

2.

(a.)

(b.)

CH 3 CH 2

CH 3 CH 2

Br

Br

+

+

CH 3 CH 2 O

CH 3

O CH 2 CH 3 CH 2 CH 3

O

O

O

C

CH 3 CH 2 O

C

CH3

+

+

Br

Br

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