Ochem 1 Review EXAM 2 PDF

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CHEM 2210 Prof. Bugarin

Exam 2 Review

Chapter 6. Chemical Reactivity and Mechanisms Review of Concepts Fill in the blanks below. To verify that your answers are correct, look in your textbook at the end of Chapter 6. Each of the sentences below appears verbatim in the section entitled Review of Concepts and Vocabulary. • ________________ reactions involve a transfer of energy from the system to the surroundings, while ______________ reactions involve a transfer of energy from the surroundings to the system. • Each type of bond has a unique ________________________ energy, which is the amount of energy necessary to accomplish homolytic bond cleavage. • Entropy is loosely defined as the ___________ of a system. • In order for a process to be spontaneous, the change in _____________ must be negative. • The study of relative energy levels and equilibrium concentrations is called ___________________.

characteristic arrow-pushing patterns:  1) ___________________, 2) ___________________, 3) ___________________, and 4) ___________________. • As a result of hyperconjugation, __________ carbocations are more stable than secondary carbocations, which are more stable than ___________ carbocations. 1. Calculate the enthalpy of the following reaction. Ans: -8 kJ/mol 2. What type of cleavage does the following reaction involve? A. homolytic B. heterolytic Ans: A 3. What type of cleavage does the following reaction involve? Ans: heterolytic 4. Predict the sign of S of the following reaction?

• ____________ is the study of reaction rates. • _____________ speed up the rate of a reaction by providing an alternate pathway with a lower energy of activation. • On an energy diagram, each peak represents a ___________________, while each valley represents ________________________. • A _________________ has an electron-rich atom that is capable of donating a pair of electrons. • An __________________ has an electrondeficient atom that is capable of accepting a pair of electrons. • For ionic reactions, there are four

A. positive B. negative C. no change Ans: B 5. Why is entropy negative for ring closures? A. Closing a ring results in fewer molecules. B. Closing a ring results in more molecules. C. Closing a ring releases energy. D. Closing a ring restricts the rotation around individual carbon-carbon bonds. Ans: D 6. Predict the sign of G for an endothermic reaction with an increase in entropy. A. positive B. negative C. no change D. cannot predict

Ans:D 7. What is the energy of activation for the following reaction?

Chapter 7A. Substitution Reactions Review of Concepts

Ans: 10 kJ/mol 8. What is the effect of a catalyst on a reaction? A. It speeds up the rate. B. It decreases the entropy. C. It changes the equilibrium. D. It makes the products more stable. Ans: A 9. Identify the nucleophilic atom(s) in the following molecule.

Ans: 10. Identify the electrophilic atom in the following molecule.

Fill in the blanks below. To verify that your answers are correct, look in your textbook at the end of Chapter 7. Each of the sentences below appears verbatim in the section entitled Review of Concepts and Vocabulary. • Substitution reactions exchange one _____________ for another. • Evidence for the concerted mechanism, called SN2, includes the observation of a __________-order rate equation. The reaction proceeds with ____________ of configuration. • SN2 reactions are said to be _____________ because the configuration of the product is determined by the configuration of the substrate. • Evidence for the stepwise mechanism, called SN1, includes the observation of a __________-order rate equation.

Ans: 11. Which of the following is the most stable cation?

• The __________ step of an SN1 process is the rate-determining step.

Ans: C

• An SN1 reaction is a stepwise process with a first-order rate equation.

12. Identify the sequence of steps in the following reaction.

A. Proton transfer, Proton transfer B. Proton transfer, Loss of leaving group C. Nucleophilic attack, Proton transfer D. Proton transfer, Nucleophilic attack Ans: D 13. Draw the structure of the following cation after rearrangement.

Ans:

• There are four factors that impact the competition between the SN2 mechanism and SN1: 1) the _____________, 2) the ________________, 3) the ___________ _______________, and 4) the _______________. • _________solvents favor SN2. 1. Which of the following is a substitution reaction?

Ans: B

CHEM 2210 Prof. Bugarin

Exam 2 Review

2. For the following reaction, label the nucleophile, electrophile, and leaving group.

Ans:

3. Which of the following is the correct IUPAC name of the following structure?

Ans:

8. Draw a reaction diagram for the following reaction.

Ans: 9. Why is a tertiary alkyl halide more reactive in an SN1 reaction than a secondary alkyl halide? Ans: The tertiary cation is more stable.

A) Chlorocyclopentane B) 2-Chloro-1-methylcyclopentane C) 1-Methyl-2-chlorocyclopentane D) 1-Chloro-2-methylcyclopentane Ans: D 4. Provide examples of the 4 patterns for steps in the mechanisms of substitution reactions. Ans: 1. Nucleophilic attack, 2. Loss of a leaving group, 3. Proton transfer, and 4. Rearrangement

10. Why does a racemate form at the leaving group carbon in an SN1 reaction? Ans: Because the cationic intermediate is planar and there is equal likelihood of attack of the nucleophile from either face, leading to equal formation of both enantiomers. 11. What is the best leaving group in the following compound?

5. Provide an arrow pushing mechanism and product for the following reaction. Ans: Ans:

6. Provide an arrow-pushing mechanism for the following (intramolecular) reaction.

12. How would you accomplish the following transformation?

Ans: MeOH (SN1 mechanism) 13. How would you accomplish the following transformation?

Ans:

7. From the given starting material, how could you stereospecifically form the given product? Ans:

Chapter 7B.Alkenes: Structure and Preparation via Elimination Reactions

2. Which of the following is the correct IUPAC name for the following compound?

Review of Concepts Fill in the blanks below. To verify that your answers are correct, look in your textbook at the end of Chapter 7. Each of the sentences below appears in the section entitled Review of Concepts and Vocabulary. • Alkene stability increases with increasing degree of ________________. • E2 reactions are said to be regioselective, because the more substituted alkene, called the ___________ product, is generally the major product. • When both the substrate and the base are sterically hindered, the less substituted alkene, called the __________ product, is the major product.

A. 2-ethyl-1,1,3-trimethylbutene B. 3-ethyl-2,4-dimethyl-2-pentene C. 2,4-dimethylhexene D. 4-ethyl-1,3-dimethyl-3-pentene Ans: B 3. Given the following alkane, draw the least stable alkene isomer with the same basic skeleton.

Ans: 4. What is the product of the following elimination?

Ans: • E2 reactions are stereospecific because they generally occur via the __________________ conformation. • Substituted cyclohexanes only undergo E2 reactions from the chair conformation in which the leaving group and the proton both occupy _________ positions. • E1 reactions exhibit a regiochemical preference for the ___________ product.

5. Draw the isomer of 2-bromo-1,1,3trimethylcyclohexane that would be more reactive in an E2 elimination.

Ans: 6. Draw the major product of the following reaction.

• E1 reactions are not stereospecific, but they are stereo___________. • Strong nucleophiles are compounds that contain a _____________ and/or are ________________.

Ans: 7. Based upon the following energy diagram, is this reaction an E1 or an E2 elimination?

• Strong bases are compounds whose conjugate acids are _______________. Ans: E1 1. How substituted is the following alkene?

Ans: Trisubstituted

8. Draw the mechanism for the following dehydration.

CHEM 2210 Prof. Bugarin

Exam 2 Review

Ans:

Chapter 8. Addition Reactions of Alkenes Review of Concepts Fill in the blanks below. To verify that your answers are correct, look in your textbook at the end of Chapter 8. Each of the sentences below appears verbatim in the section entitled Review of Concepts and Vocabulary.

9. What are the steps in the following mechanism?

Ans: Proton transfer, loss of leaving group, rearrangement, proton transfer 10. What is the structure of the rearranged carbocation in the following dehydration?

• Addition reactions are thermodynamically favorable at ____ temperature and disfavored at _____ temperature. • Hydrohalogenation reactions are regioselective, because the halogen is generally placed at the ______ substituted position, called _______________ addition. • In the presence of _____________, addition of HBr proceeds via an anti- Markovnikov addition.

Ans: 11. Is the following more likely a nucleophile or a base?

Ans: Base 12. Which of the following is the strongest nucleophile?

• The regioselectivity of an ionic addition reaction is determined by the preference for the reaction to proceed through ____________________________________. • Acid-catalyzed hydration is inefficient when ____________________________ are possible. Dilute acid favors formation of the ___________ and while concentrated acid favors the ___________. • Oxymercuration-demercuration achieves hydration of an alkene without ___________________________________.

Ans: C 13. Which of the following is most likely to act as a base rather than a nucleophile?

Ans: C

• _____________-_______________ can be used to achieve an anti-Markovnikov addition of water across an alkene. The reaction is stereospecific and proceeds via a _____ addition. • Asymmetric hydrogenation can be achieved with a ________ catalyst.

14. What is the most likely product for the following reaction?

Ans:

• Bromination proceeds through a bridged intermediate, called a ________________ ______, which is opened by an SN2 process that produces an _____ addition.

• A two-step procedure for anti dihydroxylation involves conversion of an alkene to an _________, followed by acidcatalyzed ring opening. A) • Ozonolysis can be used to cleave a double bond and produce two ______ groups. • The position of a leaving group can be changed via ______________ followed by ________________. • The position of a π bond can be changed via ______________ followed by ________________. 1. Addition reactions of alkenes are characterized by: A) formation of a π bond B) addition of two groups across a double bond C) breaking of a π bond D) A and B E) B and C Ans: E 2. In a reaction where addition and elimination reactions are in competition, which of the following statements is most correct? A) Addition and elimination reactions are favored at low temperatures. B) Addition and elimination reactions are favored at high temperatures. C) Only addition reactions are favored at low temperatures. D) Only elimination reactions are favored at low temperatures. E) Addition and elimination reactions are disfavored at low temperatures. Ans: C 3. In the addition reaction of HI to 2-methyl-2butene, the Markovnikov addition mechanism involves: A) attack of 2-methyl-2-butene initiated by an iodide ion. B) attack of 2-methyl-2-butene initiated by an iodine atom. C) isomerization of 2-iodo-2-methylbutene. D) formation of a carbocation at carbon two. E) formation of carbocation at carbon three. Ans: D 4. The expected major product of the following reaction is:

C) Ans:

B) D) C

5. The expected major product of the following reaction is:

A)

C) Ans:

B)

D) A

6. The expected major product of the following reaction is:

A) B) C) D) E) Ans:

I II III IV V D

7. What is the expected major product for the following reaction?

A) C) Ans:

B) D) B

8. What is the expected major product for the following reactions?

A)

B)

CHEM 2210 Prof. Bugarin

C) Ans:

Exam 2 Review

D) A

9. Provide the major organic product(s) for the reaction shown below.

A) C) Ans:

B) D) B

10. What is the expected major product for the following reaction?

A) B) C) D) E) Ans:

I II III IV V A

13. What is the expected major product for the following reaction?

A) B) C) D) E) Ans:

I II III IV V D

A)

B) 11. For the reaction sequence below, identify the expected major product(s). C)

D) A) B) C) D) E) Ans:

I II III I and III II and III D

12. What are the expected major products from the reaction sequence shown below?

E) Ans:

A...