Worksheet: NMR Splitting Patterns

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In this worksheet, we will practice determining molecular structure from NMR splitting patterns and assigning multiplicities based on peak intensities.

Q1:

Which of the following correctly describes the relative intensities of splitting an NMR peak?

  • AQuartet—1∶4∶4∶1
  • BTriplet—1∶3∶1
  • CPentet—1∶3∶5∶3∶1
  • DSextet—1∶5∶10∶10∶5∶1

Q2:

Which of the following causes the splitting of energy levels in the presence of a magnetic field?

  • APauli exclusion principle
  • BSymmetry degeneracy
  • CThe Zeeman effect
  • DFermi contact interaction
  • EBose–Einstein effect

Q3:

A 19F NMR spectrum at room temperature reveals one well-defined peak. When cooled slightly, the peak becomes broadened. At N2(𝑙) temperature, two well-defined peaks are apparent. What is responsible for these observations?

  • AInteger quantum spin numbers (𝐼=1,2,3,…)
  • BSpin–spin coupling interactions
  • CLow natural abundances of the 19F nucleus
  • DFractional quantum spin numbers (𝐼=1/2,3/2,5/2)
  • EDynamic fluxionality

Q4:

What is the most likely cause of fluxional behavior in the NMR spectrum of Fe(CO)5, iron pentacarbonyl?

  • ADissociation and recoordination of the carbonyl ligands
  • BOpening and closing of bridging carbonyls
  • CMonomer-dimer formation with a bridging carbonyl
  • DRotation of a hindered carbonyl bond
  • EIsomerism between trigonal bipyramidal and square pyramidal configurations

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