1H NMR Interpretation: A New Tool for Students

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1H NMR Interpretation A New Tool for Students

• John V. McClusky
• Texas Lutheran University

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Why Teach NMR Interpretation?

• Necessary for molecular identification
• Important for teaching problem solving skills
• Complex and abstract
• Must concentrate on details and big picture
• You guess, you loose

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The Process

• Students must use
• Integration
• Number of hydrogens making the peak
• Multiplicity
• Number of adjacent hydrogens
• Chemical shift
• Functional groups
• Determine the molecular structure

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The Problem

• Doesnt look like

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Typical Student Errors

• Ignore integration, multiplicity, or chemical
  shift
• Interpret peak incorrectly
• n1 or n-1?
• Switch integration and multiplicity
• Force spectrum to match preconceived molecule

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NMR Mosaic Goals

• Make NMR Interpretation more concrete
• Reinforce need to use all data
• Chemical shift
• Multiplicity
• Integration
• Visualize relationship between multiplicity and
  connectivity
• Retain all problem-solving aspects

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NMR Mosaic

• Spectral peaks
• Molecular fragments
• Molecule
• fit mismatch
• Finished Revise --

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Advantages of the NMR Mosaic

• Requires use of integration, chemical shift, and
  multiplicity
• Accentuates students interpretation errors
• Eases interpretation of complex multiplets
• Illustrates relationship between connectivity and
  multiplicity

Helps students understand and visualize NMR
interpretation
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Mosaic Pieces
Peak is from Splitting indicates
Chemical shift Final mosaic piece
a CH2 adjacent CH3 indicates
adjacent
functional group




Funct. Grp
CH3
Students add static clings to generic pieces to
produce a custom piece encoding connectivity and
functionality
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Example C3H7Cl
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Example C3H7Cl
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Example C3H7Cl
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Example C3H7Cl
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Example C3H7Cl
X-
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Example C3H7Cl
X-
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Example C3H7Cl
X-
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Example C3H7Cl
X-
1-chloropropane
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NMR Mosaic Simplifies Interpretation of Complex
Multiplets

• Adjoining pieces specify connectivity
• Interpretation is no longer impossible

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Example C4H9Cl
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Example C4H9Cl
X-
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Example C4H9Cl
X-
Undetermined Splitting
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Example C4H9Cl
X-
Undetermined Splitting
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Example C4H9Cl
X-
Undetermined Splitting
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Example C4H9Cl
X-
Undetermined Splitting
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Example C4H9Cl
2-chlorobutane
X-
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NMR Mosaic Helps Students Catch Mistakes

• Mosaic pieces no longer match
• Focus students on incorrectly interpreted peaks

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Example C3H7Cl
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Example C3H7Cl
X-
Incorrect Match ?
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Example C3H7Cl
X-
Corrected Piece Matches
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Functional Groups

• Easily used for spectra with over 10 carbons plus
  aromatic rings
• All major functional groups including
• Aromatic rings (mono and di-substituted)
• Alcohols, ethers, esters, aldehydes, ketones,
  carboxylic acids, amines
• Alkenes

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Student Experiences

• Students found the NMR Mosaic a great aid in NMR
  Interpretation
• Much higher percentage of students successfully
  solved problems
• Allows much more realistic problems on exams
• Better students weaned themselves off NMR Mosaic
  and only used it when had problems
• Students had a much stronger understanding of NMR
  interpretation

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NMR Mosaic Key Features

• Requires use of Integration, Multiplicity, and
  Chemical Shift
• Accentuates students interpretation errors
• Eases interpretation of complex multiplets
• Reinforces relationship between multiplicity and
  connectivity
• Can be used with thousands of spectra

EMPHASIZES UNDERSTANDING AND PROBLEM SOLVING
SKILLS