Chapter 4 Multiple Choice Questions

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1. What is the hyperfine value for the nitrogen atom trapped inside a C₆₀ molecule? The EPR spectrum recorded at 9.5 GHz is shown in Fig. 4.2.

0.6 G correct incorrect

6 mT correct incorrect

15.7 MHz correct incorrect

9.5 GHz correct incorrect

60 mT correct incorrect

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2. Predict the number of lines in the EPR spectrum of a solution of ¹³C-labelled methyl radical (¹³CH₃•), assuming the lines do not overlap.

4 correct incorrect

3 correct incorrect

6 correct incorrect

24 correct incorrect

8 correct incorrect

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3. Predict the number of lines in the EPR spectrum of a solution of dimethylnitroxide (CH₃)₂NO• assuming the lines do not overlap.

21 correct incorrect

3 correct incorrect

7 correct incorrect

24 correct incorrect

12 correct incorrect

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4. What is the ratio of line intensities in the EPR spectrum of the t-Bu radical (CH₃)₃C•?

1:19:36:84:126:126:84:36:19:1 correct incorrect

1:9:36:84:126:126:84:36:9:1 correct incorrect

1:9:35:82:120:120:82:35:9:1 correct incorrect

1:8:28:56:70:56:28:8:1 correct incorrect

1:10:45:120:210:252:210:120:45:10:1 correct incorrect

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5. Predict the hyperfine value for the EPR spectrum of fully deuteriated benzene radical anion C₆D₆^•-.

0.375 mT correct incorrect

3.75 G correct incorrect

2.35 mT correct incorrect

0.58 G correct incorrect

3.75 mT correct incorrect

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6. Estimate the β-hyperfine value for the cyclobutyl radical (C₄H₇•) assuming the radical is flat and the HCH angle is 115°.

4.6 mT correct incorrect

27 G correct incorrect

5.4 mT correct incorrect

3.8 mT correct incorrect

23 G correct incorrect

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7. Calculate spin density on the central carbon atom of malonic acid radical (•CH(COOH)₂) if the hyperfine value for the α-hydrogen atom is 21.9 G.

0.95 correct incorrect

0.85 correct incorrect

0.15 correct incorrect

0.65 correct incorrect

0.23 correct incorrect

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8. Which one sentence explains most accurately why spin trapping is often used to detect free radical intermediates?

spin trapping provides more structural information than direct detection by EPR correct incorrect

spin trapping makes it easy to quantify free radical intermediates correct incorrect

steady state concentration of free radical intermediates is often too low to enable direct detection by EPR correct incorrect

detection of spin adducts requires lower power than direct detection of radical intermediates correct incorrect

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9. The spectrum shown in Fig. 4.25 is composed of two ethanol radicals. Radical A shows a smaller α-hyperfine value than radical B. What is the best explanation?

radical A is less sterically shielded than radical B correct incorrect

radical B shows larger α-hyperfine value due to additional splitting from six γ-protons correct incorrect

the difference in hyperfine values is due to different dihedral angles in the two radicals correct incorrect

the unpaired electron in radical A is partially delocalised on the oxygen atom correct incorrect

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10. Calculate the hyperfine values for TEMPO at X- and W-bands (in MHz). The spectra are shown in Fig. 4.21.

X-band: 96 MHz, W-band: 960 MHz correct incorrect

X-band: 48 MHz, W-band: 4.8 MHz correct incorrect

X-band: 48 MHz, W-band: 48 MHz correct incorrect

X-band: 96 MHz, W-band: 96 MHz correct incorrect