Week 9 Chem 222 KEY - Practice Exam Chatterjee PDF

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Practice Exam Chatterjee...

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Dr. Manashi Chatterjee

Recitation Week-9 Chem-222

Write the expected final major product(s) for each of the reaction in the big box. If more than one stereoisomer is produced, give the structures of each stereoisomer and give the relationship between the stereoisomers formed. Show stereochemistry where ever required. DO NOT WRITE THE INTERMEDIATES.

Dr. Manashi Chatterjee

Practice- Week-9 Chem-222

7.

8.

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Dr. Manashi Chatterjee

Practice- Week-9 Chem-222

Draw a reaction coordinate diagram for the following reaction. Be sure to label starting material(s), transition state(s), product(s), activation energy(ies), and intermediate(s) (if applicable).

Consider the following substitution reactions. For each: a) draw the major product(s) that arise from substitution b) determine if the given substitution takes place by SN2 or SN1 (circle your answer)

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Dr. Manashi Chatterjee

Practice- Week-9 Chem-222

Complete the reaction sequence shown below. Show correct arrows to indicate how you get to the products.

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Dr. Manashi Chatterjee

Practice- Week-9 Chem-222

a) Predict the major product of the following reaction. Answers without stereochemistry will be given no credit! b) In the space below, draw a detailed arrow-pushing mechanism.

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Dr. Manashi Chatterjee

Practice- Week-9 Chem-222

Draw an arrow-pushing mechanism for the following solvolysis experiment

In each of the given pair circle the compound that reacts the fastest with sodium cyanide, NaCN?

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Dr. Manashi Chatterjee

Practice- Week-9 Chem-222

Consider the following reaction: (circle the correct answer)

1. If concentration of [alkyl halide] is doubled rate a. quartered

b. Halved

c. Same d. Doubled

e. Quadrupled

2. If concentration of [CH3SH] is doubled rate a. quartered

b. Halved

c. Same d. Doubled

e. Quadrupled

3. If concentration of both are doubled rate a. quartered

b. Halved

c. Same d. Doubled

e. Quadrupled

Consider the following reaction:

1. If concentration of [(CH3)3CBr] is doubled rate a. quartered

b. Halved

c. Same d. Doubled

e. Quadrupled

2. If concentration of [NaCN] is doubled rate a. quartered

b. Halved

c. Same d. Doubled

e. Quadrupled

3. If concentration of both are doubled rate a. quartered

b. Halved

c. Same d. Doubled

e. Quadrupled

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Dr. Manashi Chatterjee

Practice- Week-9 Chem-222

Circle the compound below that meets the criteria and provide an explanation for your answer. a. reacts fastest with NaSCH2CH3 _by SN2_________

b. reacts fastest with NaCN ___by___ SN2_________

c. reacts fastest with 1-bromobutane: __by_ SN2______ O

CH3CH2OH

CH3CHONa

CH3C

ONa

CH3CH2CH3

Circle the compound below that meets the criteria and provide an explanation for your answer.

Rank the following in terms of SN2 nucleophilicity from most to least (explain in 1ess than 10 words) NH3

H2O

H 2S

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Dr. Manashi Chatterjee

Practice- Week-9 Chem-222

H2S > NH3 > H2O Less electronegative element will donate its electrons readily and act as better nucleophiles

Rank the following substrate in terms of predicted SN2 reaction with NaN3 from most to least (explain in 1ess than 10 words)

More steric (tertiary alkyl halides) can not be attacked by nucleophiles in one step from the back. Rank the following carbocations in order of stability

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Dr. Manashi Chatterjee

Practice- Week-9 Chem-222

Even though they are primary halides, the neopentyl halides are very unreactive towards SN2 substitution. Explain in less than 15 words.

Cl

Backside attack is prevented due to steric crowding of the 3 methyl groups near the carbon containing the leaving group. The nucleophile can not reach the electrophilic carbon (the carbon attached to the leaving group)

For the reaction of 2-bromo-2-methylpropane in water, show the intermediate formed in the rate determining step. For the reaction of 2-bromo-2-methylpropane in water, show the intermediate formed in the rate determining step.

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Dr. Manashi Chatterjee

Practice- Week-9 Chem-222

Would this reaction occur more rapidly or slowly for 2-bromopropane? Answer in terms of the intermediate and rate determining step when compared to part a. Slow for 2-bromopropane; intermediate carbocation is secondary. Tertiary carbocation is more stable than secondary carbocation. Intermediate for 2-bromobutane is less stable high energy reaction will be slower.

Draw the transition state for the SN2 reaction of the anion of NaCN with ethyl bromide.

Which of the following compounds in the given pair reacts the slowest with sodium azide, NaN3?

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Dr. Manashi Chatterjee

Practice- Week-9 Chem-222

Draw the two chair forms of (1S,2S)-1chloro-2-methylcyclohexane and Indicate which one will be more stable. The framework is provided

Δ G0 (kcal mol-1) -CH3 : 1.7 -SCH3: 0.95 -Cl: 0.52

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Dr. Manashi Chatterjee

Practice- Week-9 Chem-222

Circle the alkyl halide among each of the given pairs, that you expect to react more rapidly by an SN2 mechanism? Give a concise explanation of your selection in less than 10 words. 1.

Br

Br

(A)

(B)

primary alkyl halides are sterically less hindered and react faster under one step S N2 mechanism; A is primary alkyl halide B is a secondary alkyl halide 2. Br Br

(A)

(B)

Leaving group is attached to a sp2 Carbon in A; the approach of the nucleophile is prevented due to the pi electron on the benzene ring; Leaving group on compound B is on a sp3 Carbon and away from the pi cloud where the nucleophile can attack readily. 3. (CH3)2CHCH2CH2I (A)

(CH3)2CHCH2I (B)

Compound A has a branch that are far away from the leaving group so sterically less hindered; Branch in B is closer to the leaving group adding steric hindereance that prevents the nucleophile to reach the reaction center.

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Dr. Manashi Chatterjee

Practice- Week-9 Chem-222

Draw a detailed mechanism that accounts for each of the following products

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Dr. Manashi Chatterjee

Practice- Week-9 Chem-222

Answer: C

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Dr. Manashi Chatterjee

Practice- Week-9 Chem-222

Identify the reactants, products, energy of activation and ΔGo on the following energy diagram.

A

B C

Free Energy (G)

D Reaction Coordinate

1. ΔGo 2. Energy of Activation 3. Products 4. Reactants A: B: C: D: Answer is: A: 4 B: 2 C: 1 D: 3

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Dr. Manashi Chatterjee

Practice- Week-9 Chem-222

Answer is: a, e.

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Dr. Manashi Chatterjee

Practice- Week-9 Chem-222

show arrows from Br- to the carbocations.

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