Question 1

Circle the sp2-hybridized carbons in the structure.

Accepted Answer

The central carbon of the cumulated double bond is sp-hybridized.

Question 2

Draw the thermodynamic and kinetic product for the reaction. Clearly identify which is the thermodynamic and kinetic product.

Accepted Answer

The diene contains two alkenes that can each be protonated by the HBr. Four possible carbocations can be formed.
   The bromine will add to the tertiary allylic carbocation to generate the kinetic product.
   The tertiary allylic carbocation is in resonance with the secondary allylic carbocation. Bromine addition to this carbocation will give the thermodynamic product. This is the thermodynamic product since the alkene is more substituted and more stable.

Question 3

Give the structure of the diene and dienophile that would give this product after a Diels-Alder reaction.

Accepted Answer

In a Diels-Alder reaction, the two carbons of the double bond and the two adjacent carbons came from the diene. None of these carbons are substituted, so the diene must have been 1,3-butadiene. The remaining carbons of the ring came from the dienophile. The dienophile must have been a trans alkene, since the stereochemistry of the alkene is retained in the product.

Question 4

Deduce the starting materials that would give this compound via the Diels-Alder reaction.

Accepted Answer

In a Diels-Alder reaction, the two carbo

Question 5

Which compound has UV absorption at the greatest wavelength?

Accepted Answer

A)  compound A 
B)  compound B 
C)  compound C 
D)  compound D 
A)  compound A 
B)  compound B 
C)  compound C 
D)  compound D

Question 6

Which of these dienes cannot undergo the Diels-Alder reaction.

Accepted Answer

A)  compound A 
B)  compound B 
C)  compound C 
D)  compound D 
A)  compound A 
B)  compound B 
C)  compound C 
D)  compound D

Question 7

Draw the endo product formed in the Diels-Alder reaction. Clearly show stereochemistry, where applicable.

Accepted Answer

When a cis alkene reacts with a diene in

Question 8

An arginine residue and a phenylalanine residue are located close to each other in a protein structure.
  Select the most favorable interaction(s) of arginine and phenylalanine.

Accepted Answer

A)  offset stacking 
B)  edge-to-face interaction 
C)  pi-cation interaction 
A)  offset stacking 
B)  edge-to-face interaction 
C)  pi-cation interaction

Question 9

All but one of these molecules are active ingredients in commercial sunscreens. Which compound does not act as a sunscreen?

Accepted Answer

A)  compound A 
B)  compound B 
C)  compound C 
D)  compound D 
A)  compound A 
B)  compound B 
C)  compound C 
D)  compound D

Question 10

The diene reacts with HBr to give two isomers A and B (C6H11Br).
   ​a. Give the structures of A and B.
b. Give the structure of the carbocation intermediate involved in this reaction. Be sure to show any relevant resonance structures.
c. When compounds A and B are each treated under solvolysis conditions with acetone/water, each compound forms a mixture of the same two alcohols C and D. Give the structures of these two alcohols and explain why both are formed from each alkyl halide.

Accepted Answer

a. The products are the 1,2- and 1,4-add

Question 11

The reaction of an allylic alcohol with HBr generates the two products shown. Draw a curved arrow mechanism to explain how both products are formed.

Accepted Answer

The first step is protonation of the alc

Question 12

Draw the major organic product of this reaction.

Accepted Answer

The starting material is a diene and the

Question 13

Which compound or ion has a UV/visible absorption at the greatest wavelength?

Accepted Answer

A)  compound A 
B)  compound B 
C)  compound C 
D)  compound D 
E)  compound E 
A)  compound A 
B)  compound B 
C)  compound C 
D)  compound D 
E)  compound E

Question 14

Which of these compounds is aromatic?

Accepted Answer

A)  compound A 
B)  compound B 
C)  compound C 
D)  compound D 
A)  compound A 
B)  compound B 
C)  compound C 
D)  compound D

Question 15

Determine whether each compound is aromatic, antiaromatic, or neither. Label each compound with the pi-electron count.

Accepted Answer

Compound A has ten pi electrons in a con

Question 16

Draw a Frost circle and determine the molecular orbitals and electron occupancies for furan.

Accepted Answer

Furan is a cyclic conjugated ring with f

Question 17

1,3-Cyclopentadiene is unusually acidic, with a pKa of ~16. On the other hand, 1,3,5-cyclohepatriene is much less acidic, with a pKa of ~36. Explain why the compounds have such differing acidities.

Accepted Answer

Deprotonation of one of the sp³ hydrogens

Question 18

Select all structures that contain conjugated pi bonds.

Accepted Answer

A)  compound A 
B)  compound B 
C)  compound C 
D)  compound D 
E)  compound E 
A)  compound A 
B)  compound B 
C)  compound C 
D)  compound D 
E)  compound E

Question 19

Pyridine and pyrrole are both aromatic nitrogen-containing rings. Explain how the lone pair on each nitrogen contributes or does not contribute to the pi electron count.

Accepted Answer

Pyridine is like a benzene ring, except

Question 20

The Diels-Alder reaction can give two constitutional isomeric products, A and

Accepted Answer

The two different products can be formed

Exam 15: Dienes and Aromaticity

Circle the sp2-hybridized carbons in the structure.

Draw the thermodynamic and kinetic product for the reaction. Clearly identify which is the thermodynamic and kinetic product.

Give the structure of the diene and dienophile that would give this product after a Diels-Alder reaction.

Deduce the starting materials that would give this compound via the Diels-Alder reaction.

Which compound has UV absorption at the greatest wavelength?

Which of these dienes cannot undergo the Diels-Alder reaction.

Draw the endo product formed in the Diels-Alder reaction. Clearly show stereochemistry, where applicable.

An arginine residue and a phenylalanine residue are located close to each other in a protein structure. Select the most favorable interaction(s) of arginine and phenylalanine.

All but one of these molecules are active ingredients in commercial sunscreens. Which compound does not act as a sunscreen?

The reaction of an allylic alcohol with HBr generates the two products shown. Draw a curved arrow mechanism to explain how both products are formed.

Draw the major organic product of this reaction.

Which compound or ion has a UV/visible absorption at the greatest wavelength?

Which of these compounds is aromatic?

Determine whether each compound is aromatic, antiaromatic, or neither. Label each compound with the pi-electron count.

Draw a Frost circle and determine the molecular orbitals and electron occupancies for furan.

1,3-Cyclopentadiene is unusually acidic, with a pKa of ~16. On the other hand, 1,3,5-cyclohepatriene is much less acidic, with a pKa of ~36. Explain why the compounds have such differing acidities.

Select all structures that contain conjugated pi bonds.

Pyridine and pyrrole are both aromatic nitrogen-containing rings. Explain how the lone pair on each nitrogen contributes or does not contribute to the pi electron count.

The Diels-Alder reaction can give two constitutional isomeric products, A and

Chemical Bonding and Chemical Structure

Alkanes and Organic Nomenclature

The Curved-Arrow Notation, Resonance, Acids and Bases, and Chemical Equilibrium

Introduction to Alkenes and Alkynes

Addition Reactions of Alkenes and Alkynes

Principles of Stereochemistry

Cyclic Compounds and Reaction Stereochemistry

Nomenclature and Noncovalent Intermolecular Interactions

The Chemistry of Alkyl Halides

Free-Radical Reactions, Main-Group Organometallic Compounds, and Carbenes

The Chemistry of Alcohols and Thiols

The Chemistry of Ethers, Epoxides, Glycols, and Sulfides

Introduction to Spectroscopy

Nuclear Magnetic Resonance Spectroscopy

The Chemistry of Benzene and Its Derivatives

Allylic and Benzylic Reactivity

The Chemistry of Aryl Halides, Vinylic Halides, and Phenols

The Chemistry of Aldehydes and Ketones

The Chemistry of Carboxylic Acids

The Chemistry of Carboxylic Acid Derivatives

The Chemistry of Enolate Ions, Enols, and Α,β-Unsaturated Carbonyl Compounds

The Chemistry of Amines

Carbohydrates

The Chemistry of Thioesters, Phosphate Esters, and Phosphate Anhydrides

The Chemistry of the Aromatic Heterocycles and Nucleic Acids

Amino Acids, Peptides, and Proteins

Pericyclic Reactions

Filters

Circle the sp²-hybridized carbons in the structure.

1,3-Cyclopentadiene is unusually acidic, with a pK_a of ~16. On the other hand, 1,3,5-cyclohepatriene is much less acidic, with a pKa of ~36. Explain why the compounds have such differing acidities.