Question 1

A compound with molecular formula $\mathrm{C}_5\mathrm{H}_8$ is analyzed. What is its degree of unsaturation (HDI)?

Accepted Answer

HDI = $2$

Question 2

Which of the following statements about the $^1\mathrm{H}$ NMR spectrum of ethyl acetate ($\mathrm{CH}_3\mathrm{COOCH}_2\mathrm{CH}_3$) is correct?

Accepted Answer

The methylene protons ($\mathrm{CH}_2$) next to oxygen will appear as a quartet.

Question 3

How many unique $^1\mathrm{H}$ NMR signals would you expect for 2,2-dimethylpropane ($\mathrm{C}_5\mathrm{H}_{12}$)?

Accepted Answer

1

Question 4

A compound with molecular formula $\mathrm{C}_4\mathrm{H}_8\mathrm{O}$ shows three $^1\mathrm{H}$ NMR signals: a singlet at $\delta 2.1$ (3H), a quartet at $\delta 2.7$ (2H), and a triplet at $\delta 1.1$ (3H). What is the most likely structure?

Accepted Answer

Butanone ($\mathrm{CH}_3\mathrm{COCH}_2\mathrm{CH}_3$)

Question 5

In a DEPT-135 $^{13}\mathrm{C}$ NMR experiment, which type of carbon atom will appear as a negative (downward) signal?

Accepted Answer

$\mathrm{CH}_2$ carbons

Question 6

Which of the following is the correct IUPAC name for a conjugated diene with an alkyl group at position 2 and a hydroxyl group at position 4: $\mathrm{CH}_2=CH-CH=CH-CH_2OH$?

Accepted Answer

4-hydroxy-1,3-pentadiene

Question 7

Which method is commonly used to prepare conjugated dienes from alkenes?

Accepted Answer

Dehydrohalogenation of dihalides

Question 8

When 1,3-butadiene reacts with HBr at low temperature, which product is favored?

Accepted Answer

1,2-adduct: $\mathrm{CH}_2Br-CH=CH-CH_3$

Question 9

In the Diels-Alder reaction between 1,3-butadiene and maleic anhydride, which statement is correct regarding the stereochemistry of the product?

Accepted Answer

The product is a cis-fused bicyclic compound

Question 10

Which of the following best describes the outcome of a thermal electrocyclic reaction of a 4 $\pi$ electron system (such as 1,3-butadiene)?

Accepted Answer

Conrotatory ring closure

Question 11

According to the Woodward-Hoffmann rules, what is the stereochemical outcome for a photochemical electrocyclic ring closure of a 6 $\pi$ electron system (such as hexatriene)?

Accepted Answer

Disrotatory ring closure

Question 12

Which of the following is a (3,3) sigmatropic rearrangement?

Accepted Answer

Claisen rearrangement

Question 13

Which statement best describes the Cope rearrangement?

Accepted Answer

A (1,5) sigmatropic rearrangement involving only carbon atoms

Question 14

A Claisen rearrangement involves which type of reactant?

Accepted Answer

An allyl vinyl ether

Question 15

Which of the following best explains why the Diels-Alder reaction is stereospecific?

Accepted Answer

The stereochemistry of the diene and dienophile is preserved in the product

Question 16

Which of the following is true about the $^1\mathrm{H}$ NMR splitting pattern for a methyl group ($\mathrm{CH}_3$) adjacent to a methylene group ($\mathrm{CH}_2$)?

Accepted Answer

It appears as a triplet due to the $n+1$ rule

Question 17

A molecule with formula $\mathrm{C}_3\mathrm{H}_6\mathrm{Br}_2$ shows two $^1\mathrm{H}$ NMR signals. Which structure is most consistent with this data?

Accepted Answer

1,3-dibromopropane

Question 18

Which of the following statements about cycloaddition reactions is correct?

Accepted Answer

[4+2] cycloaddition requires a diene and a dienophile

Question 19

A compound with formula $\mathrm{C}_4\mathrm{H}_6$ shows two $^1\mathrm{H}$ NMR signals, both singlets. Which structure is most likely?

Accepted Answer

Dimethylacetylene ($\mathrm{CH}_3\mathrm{C}\equiv\mathrm{C}\mathrm{CH}_3$)

Exam 2 Study Guide: NMR, Conjugated Systems, and Pericyclic Reactions

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