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Chemistry LibreTexts

Quiz 1 Answer Key

1. Multiple Choice and Ranking (14 pts):

Q1a

 Which of the following is not a common reagent that can oxidize an alcohol:

  1. KMnO4
  2. alcohol dehydrogenase
  3. H2CrO4
  4. ZnCl2
  5. IBX
  6. Bleach (NaOCl)

S1a

  • ZnCl2

Q1b

The inversion of stereochemistry for an SN2 reaction is explained based on collision of a nucleophile to fill what acceptor orbital?

  1. a \(\sigma\)bonding orbital
  2.  a \(\sigma*\) antibonding orbital 
  3. a \(\pi\) bonding orbital
  4. a \(\pi*\) antibonding orbital
  5. an empty \(p\) orbital

S1b

  • a s* antibonding orbital

Q1c

Which is not a property evaluated when considering 1-butanol as an advanced biofuel option?

  1. solubility in water
  2. boiling point
  3. energy density
  4. ability to be produced from renewable feedstock
  5. compatibility with current engine technology
  6. reactivity in an SN2 reaction

S1c

  F) reactivity in an SN2 reaction

Q1d

d) Rank the following compounds in order of increasing boiling point (where 1 = lowest BP and 3 = highest BP) and briefly explain your answer.

S1d

BP trend is determined by the strength of intermolecular forces between molecules (stronger intermolecular forces requires more energy). Hydrogen-bonding is a special type of dipole-dipole force that occurs in polar molecules, but it is stronger than normal dipole-dipole interactions because the O-H is more polar. Diethyl ether has normal dipole-dipole interactions due to the polar C-O bond, but does not have hydrogen-bonding forces.  1-pentanol has an alcohol group that can associate with other alcohols through hydrogen-bonding interactions, which is stronger than the dipole-dipole forces for diethyl ether. 1,4-butanediol has two alcohol groups, so that there are more hydrogen-bonding interactions, causing the BP to be the highest of the three molecules.

Q1e

e) Rank the following compounds in order of increasing acidity (where 1 = least acidic and 3 = most) and briefly explain your answer.S

S1e

 

The acidity trend is based on the inductive effect of the halide atoms and the electronegativity of the atoms where a more electronegative atom has a stronger inductive effect.  The inductive effect stabilizes the conjugate base (i.e. stabilizes the anion).  The electronegativity trend is F > Cl > H, so the trifluoroethanol is more acidic than the trichloroethanol, and the ethanol is least acidic.

Q2

2. (6 pts) The compound shown below is the derivative of a pharmaceutical lead compound that exhibits antilipidemic activity.  Identify (circle) which alcohol group has the most acidic proton, then draw the conjugate base and explain your answer.

  

S2

B is more acidic because it has resonance to stabilize the anion, with a total of three resonance contributors and the anion shared over two oxygen atoms.  (C also has some resonance, but only a total of two resonance contributors and not with another oxygen atom.  A is attached to an sp3 carbon so there is NO resonance.)

Q3

3. (8 pts) Propose a structure for the product of the following reaction and a mechanism for its formation.

     

S3

Solution is....

Q4

4. (8 pts) For each of the following mechanistic steps, show the flow of electrons using curved arrows and identify the donor and acceptor orbitals that are involved:


S4

 

Q5

5. (10 pts) Fill in the boxes to give the major product for each of the following reactions: 

 

  

 

S5

Q6a

(10 pts) a) Give the major product for the following reaction:

Q6b

Draw the structure of the anion that is the leaving group for step 1 (above), and explain why this is a good leaving group.

Q6c

Propose a structural modification from your answer in part b that would make an even better leaving group and explain why it would be a better leaving group. (this is NOT asking you to try to remember a structure we talked about in lecture, but instead to propose a new structure based on your working knowledge of organic chemistry.  There are several correct answers)