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Lesson: NMR Splitting Patterns

In this lesson, we will learn how to determine molecular structure from NMR splitting patterns and assign multiplicities based on peak intensities.

Worksheet • 4 Questions

Q1:

The splitting of energy levels in the presence of a magnetic field is caused by which of the following?

  • AThe Zeeman effect
  • BBose-Einstein effect
  • CPauli exclusion principle
  • DFermi contact interaction
  • ESymmetry degeneracy

Q2:

A 1 9 F NMR spectrum at room temperature reveals one well-defined peak. When cooled slightly, the peak becomes broadened. At N 2 ( 𝑙 ) temperatures, two well defined peaks are apparent. What is responsible for these observations?

  • ADynamic fluxionality
  • BLow natural abundances of the 1 9 F nucleus
  • CSpin-spin coupling interactions
  • DFractional quantum spin numbers ( 𝐼 = 1 / 2 , 3 / 2 , 5 / 2 )
  • EInteger quantum spin numbers ( 𝐼 = 1 , 2 , 3 , … )

Q3:

What is the most likely cause of fluxional behavior in the NMR spectrum of F e ( C O ) 5 , iron pentacarbonyl?

  • AIsomerism between trigonal bipyramidal and square pyramidal configurations
  • BMonomer-dimer formation with a bridging carbonyl
  • CDissociation and recoordination of the carbonyl ligands
  • DOpening and closing of bridging carbonyls
  • ERotation of a hindered carbonyl bond

Q4:

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

  • ASextet— 1 ∶ 5 ∶ 1 0 ∶ 1 0 ∶ 5 ∶ 1
  • BTriplet— 1 ∶ 3 ∶ 1
  • CPentet— 1 ∶ 3 ∶ 5 ∶ 3 ∶ 1
  • DQuartet— 1 ∶ 4 ∶ 4 ∶ 1
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