Chemistry Midterm III Practice Exam
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Questions and Answers

Which of the following is (2S,3R)-2,3-dihydroxybutanal?

  • Compound I and II
  • Compound II
  • Compound I
  • Compound III (correct)

What is the percentage composition of enantiomers in the given mixture with an observed specific rotation of +11.2?

  • 60% (R), 40% (S)
  • 40% (R), 60% (S)
  • 64% (R), 36% (S) (correct)
  • 36% (R), 64% (S)

What type of isomers are molecules I and II?

  • Constitutional isomers (correct)
  • Identical
  • Diastereomers
  • Enantiomers

Which of the following pairs are enantiomers?

<p>B and C (B)</p> Signup and view all the answers

Which statements about 1,1-dicyclopentanyl ethane are correct?

<p>It has a chiral center. (B), It does not have a chiral center. (C)</p> Signup and view all the answers

What is the IUPAC name for the compound represented?

<p>(3S, 4R) - 4-ethyl-3-methylheptane (C)</p> Signup and view all the answers

How many stereoisomers can be drawn for 3,3,5-trimethylhept-1-en-6-yne?

<p>4 (C)</p> Signup and view all the answers

What is the IUPAC name of the given compound?

<p>(3R,5 R)-5-fluoro-3,5-dimethylhept-1-yne (B)</p> Signup and view all the answers

Which of the following compounds is a meso compound?

<p>A compound with two or more chiral centers and an internal plane of symmetry (A)</p> Signup and view all the answers

Which statement about the SN1 mechanism is incorrect?

<p>The SN1 mechanism involves a single step. (A)</p> Signup and view all the answers

Which feature distinguishes constitutional isomers from other types of isomers?

<p>They have the same molecular formula but different structural formulas. (A)</p> Signup and view all the answers

What is necessary for a compound to be classified as enantiomers?

<p>They must have different connectivity and be mirror images. (C)</p> Signup and view all the answers

What is the initial rate of the reaction given k = 2.0 x 10^-2 M^-1s^-1, [CH3Br] = 0.2 M, and [OH-] = 0.5 M?

<p>2.0 x 10^-2 M/s (C)</p> Signup and view all the answers

Which of the following molecules is NOT likely to be chiral?

<p>A symmetrical molecule with two chiral centers. (A), A compound with one chiral center and an internal plane of symmetry. (B)</p> Signup and view all the answers

In molecular structure representation, what designates a molecule as diastereomers?

<p>They have multiple stereocenters and differ at one or more but not all. (A)</p> Signup and view all the answers

In which scenario do nucleophilicities not parallel basicities?

<p>When nucleophilic atoms are different (B)</p> Signup and view all the answers

Which statement about the nucleophiles I − and F − is correct in different solvent types?

<p>I − is stronger in protic solvents (A)</p> Signup and view all the answers

What is the correct order of leaving group ability in nucleophilic substitution reactions?

<p>Br− &gt; Cl− &gt; OH− &gt; H− (D)</p> Signup and view all the answers

Which compound arrangement depicts the correct order of increasing SN1 reaction rates?

<p>IV &lt; II &lt; III &lt; I (C)</p> Signup and view all the answers

Which solvent favors an SN1 reaction over SN2?

<p>Polar, protic solvent (B)</p> Signup and view all the answers

What is the order of increasing SN2 reaction rates for the given compounds?

<p>IV &lt; II &lt; III &lt; I (C)</p> Signup and view all the answers

Which solvent would likely yield the fastest reaction rate for nucleophilic substitution?

<p>Acetone (C)</p> Signup and view all the answers

Which statement correctly describes the relationship between solvent type and the SN2 mechanism?

<p>SN2 reactions are favored by polar aprotic solvents (A)</p> Signup and view all the answers

Flashcards

Constitutional Isomers

Molecules with the same molecular formula but different structural arrangements.

Enantiomers

Non-superimposable mirror images of each other.

Diastereomers

Stereoisomers that are not mirror images.

Chiral Center

A carbon atom bonded to four different groups.

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Stereoisomers (3,3,5-trimethylhept-1-en-6-yne)

Isomers that differ in the arrangement of atoms in space.

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Meso Compound

A molecule with chiral centers but an overall achiral structure (superimposable on its mirror image).

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Stereochemical Possibilities (3,3,5-trimethylhept-1-en-6-yne)

The number of possible spatial arrangements. This specific example would have a number of stereochemical possibilities.

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1,1-Dicylcopentanyl Ethane

A compound potentially having a chiral center depending on its specific structure. Further information is needed to conclude whether it has a chiral center or not

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Enantiomers

Molecules that are mirror images of each other but are not superimposable.

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(2S,3R)-2,3-dihydroxybutanal

A specific chiral molecule with designated stereochemistry at two carbon atoms, part of a class of compounds.

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Specific Rotation

A measure of the rotation of plane-polarized light by an optically active substance.

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SN1 Reaction

A unimolecular nucleophilic substitution reaction involving a carbocation intermediate.

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SN2 Reaction

A bimolecular nucleophilic substitution reaction occurring in a single step.

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IUPAC name

The systematic naming of a chemical compound according to a set of rules.

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Rate Constant

A proportionality constant that quantifies how quickly a chemical reaction proceeds.

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Chirality

A property of a molecule that lacks reflection symmetry.

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Nucleophile-basicity relationship

Nucleophilicity (ability to donate electrons) often parallels basicity (ability to accept protons) for nucleophiles with the same atom. However, this generally isn't true when nucleophiles have different atoms.

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Nucleophile strength in protic solvent

Nucleophiles in protic solvents (like water or alcohol) often have more available electrons to share because they don't become heavily associated with the solvent.

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Nucleophile strength in aprotic solvent

Nucleophiles in aprotic solvents (without readily accepting protons, like acetone) can be strongly affected by charge interactions. This can lead to differences in nucleophilicity compared to basicity

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Leaving group ability order

The ability of a group to leave a molecule in nucleophilic substitution reactions, Br⁻ > Cl⁻ > OH⁻ > H⁻

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SN1 reaction rate factors (solvents)

SN1 reactions, which proceed through carbocation intermediates, are favored by polar protic solvents, such as water; polar solvents help stabilize the carbocation intermediate.

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SN2 reaction rate factors (solvents)

SN2 reactions, which proceed through a backside attack, are favored by polar aprotic solvents. These solvents don't interfere with the nucleophilic attack.

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Fastest solvent for a reaction

The solvent which supports the fastest reaction rate depends on the specific reaction type.

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Rate factors in SN2

Consider factors like steric hindrance, nucleophile strength, and the leaving group ability to determine the rate of an SN2 reaction.

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Study Notes

Instructions for Practice Exam

  • Use a pen to write your name on the scantron and the exam.
  • Match the names on both.
  • Answer questions 1-18 on the scantron using a pencil.
  • Answer questions 19-23 on the exam sheet, with the indicated point values.
  • Transfer answers to the scantron in time.
  • No extra time will be given for transferring answers.
  • Plagiarism will result in a 0 grade and expulsion from the exam.
  • No pages may be removed from the exam.

Periodic Table Information

  • A periodic table is provided, with atomic numbers, symbols, and atomic weights.
  • Separate sections for lanthanide and actinide series are included.

Relative Strength of Acids and Conjugate Bases

  • A table of selected acids, their approximate pKa values, and their conjugate bases are listed.

Midterm III Practice Exam Questions (Pages 2-3)

  • Question 1: I and II are constitutional isomers, enantiomers, identical, diastereomers, or not isomeric. 
  • Question 2: 1,1-dicyclopentanyl ethane does, or does not, have a chiral center. 
  • Question 3: Number of stereoisomers for 3,3,5-trimethylhept-1-en-6-yne.
  • Question 4: Determine which molecules are meso compounds.
  • Other specific questions on various organic chemistry topics including structural formulas, isomers, chiral centers, and reactions (SN1 and SN2).

Additional Questions (Pages 4-7)

  • Question 5: Identify a specific compound (2S,3R)-2,3-dihydroxybutanal. 
  • Question 6: Determine percentages of isomers (R and S) in a mixture given specific rotation,
  • Questions 7-18: Various organic chemistry questions on molecules, reactions, and stereochemistry.
  • Questions 19-23: Additional organic chemistry problems that require reactions, formulas or structures.

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Description

Prepare for your Chemistry Midterm III with this practice exam! This quiz covers essential topics such as the periodic table, relative strength of acids and their conjugate bases, and various isomer classifications. Test your knowledge and boost your confidence before the big day.

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