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1 H NMR Interpretation: A New Tool for Students. John V. McClusky Texas Lutheran University. Why Teach NMR Interpretation?. Necessary for molecular identification Important for teaching problem solving skills Complex and abstract Must concentrate on details and big picture - PowerPoint PPT Presentation
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Texas Lutheran University
1H NMR Interpretation: A New Tool for Students
John V. McClusky
Texas Lutheran University
Texas Lutheran University
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
Doesn’t look like
11 10 9 8 7 6 5 4 3 2 1
300 MHz ¹H NMR C13H16O3
ALL RIGHTS RESERVED © Sigma-Aldrich Co.
OH
O
O
CH3
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Typical Student Errors
• Ignore integration, multiplicity, or chemical shift
• Interpret peak incorrectly– n+1 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 student’s interpretation errors
• Eases interpretation of complex multiplets
• Illustrates relationship between connectivity and multiplicity
Helps students understand andvisualize NMR interpretation
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Mosaic Pieces
H | ─C─ | H
CH
3 Fun
ct. G
rp.
CH3
Fun
ct. G
rp
+ + = H | ─C─ | H
Peak is from Splitting indicates Chemical shift Final mosaic piece a CH2 adjacent CH3 indicates adjacent functional group
Students add static clings to generic pieces to produce a custom piece encoding connectivity and
functionality
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300 MHz ¹H NMRIn CDCl3
ALL RIGHTS RESERVED© Sigma-Aldrich Co.
Example: C3H7Cl
Texas Lutheran University
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300 MHz ¹H NMRIn CDCl3
ALL RIGHTS RESERVED© Sigma-Aldrich Co.
Example: C3H7Cl
H | ─C─ | H
Texas Lutheran University
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300 MHz ¹H NMRIn CDCl3
ALL RIGHTS RESERVED© Sigma-Aldrich Co.
Example: C3H7Cl
H | ─C─ | H
CH2
Texas Lutheran University
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300 MHz ¹H NMRIn CDCl3
ALL RIGHTS RESERVED© Sigma-Aldrich Co.
Example: C3H7Cl
H | ─C─ | H
CH2 Fun
ct. G
rp.
Texas Lutheran University
Example: C3H7Cl
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300 MHz ¹H NMRIn CDCl3
ALL RIGHTS RESERVED© Sigma-Aldrich Co.
X-
H | ─C─ | H
CH2 Fun
ct. G
rp.
Texas Lutheran University
Example: C3H7Cl
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300 MHz ¹H NMRIn CDCl3
ALL RIGHTS RESERVED© Sigma-Aldrich Co.
H | ─C─ | H
CH2 Fun
ct.
Grp
.
X-
H | ─C─ | H
CH2
CH3
Texas Lutheran University
Example: C3H7Cl
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300 MHz ¹H NMRIn CDCl3
ALL RIGHTS RESERVED© Sigma-Aldrich Co.
H | ─C─ | H
CH2 Fun
ct.
Grp
.
X-
H | ─C─ | H
CH2
CH3
H |H─C─ | H
CH2
Texas Lutheran University
Example: C3H7Cl
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300 MHz ¹H NMRIn CDCl3
ALL RIGHTS RESERVED© Sigma-Aldrich Co.
H | ─C─ | H
CH2 Fun
ct.
Grp
.
X-
H | ─C─ | H
CH2
CH3
H |H─C─ | H
CH2
1-chloropropane
Texas Lutheran University
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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5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5
300 MHz ¹H NMRIn CDCl3
ALL RIGHTS RESERVED© Sigma-Aldrich Co.
Texas Lutheran University
Example: C4H9Cl
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1.00
5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5
300 MHz ¹H NMRIn CDCl3
ALL RIGHTS RESERVED© Sigma-Aldrich Co.
X- H | ─C─ |
Fun
ct. G
rp.
CH
3CH2
Texas Lutheran University
Example: C4H9Cl
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1.00
5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5
300 MHz ¹H NMRIn CDCl3
ALL RIGHTS RESERVED© Sigma-Aldrich Co.
X- H | ─C─ |
Fun
ct. G
rp.
CH
3CH2
H | ─C─ | H
Undetermined
Splitting
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Example: C4H9Cl
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1.00
5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5
300 MHz ¹H NMRIn CDCl3
ALL RIGHTS RESERVED© Sigma-Aldrich Co.
X- H | ─C─ |
Fun
ct. G
rp.
CH
3CH2
H | ─C─ | H
Undetermined
Splitting
H |H─C─ | H
CH
Texas Lutheran University
Example: C4H9Cl
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1.00
5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5
300 MHz ¹H NMRIn CDCl3
ALL RIGHTS RESERVED© Sigma-Aldrich Co.
X- H | ─C─ |
Fun
ct. G
rp.
CH
3CH2
H | ─C─ | H
Undetermined
Splitting
H |H─C─ | H
CH
H |H─C─ | H
CH2
Texas Lutheran University
Example: C4H9Cl
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1.00
5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5
300 MHz ¹H NMRIn CDCl3
ALL RIGHTS RESERVED© Sigma-Aldrich Co.
X-
H | ─C─ |
Fun
ct. G
rp.
CH
3CH2
H | ─C─ | H
Undetermined
Splitting
H
|
H─
C─
|
H
CH
H |H─C─ | H
CH2
Texas Lutheran University
Example: C4H9Cl
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0.75
1.00
5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5
300 MHz ¹H NMRIn CDCl3
ALL RIGHTS RESERVED© Sigma-Aldrich Co.
X-
H | ─C─ |
Fun
ct. G
rp.
CH
3CH2
H
|
H─
C─
|
H
CH
H |H─C─ | H
CH2 H | ─C─ | H
CH
CH3
2-chlorobutane
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NMR Mosaic Helps Students Catch Mistakes
• Mosaic pieces no longer match
• Focus students on incorrectly interpreted peaks
Texas Lutheran University
Example: C3H7Cl
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300 MHz ¹H NMRIn CD Cl3
A LL RIG H TS RESERV ED© S igm a-A ldrich Co.
H|
H─C─|H
CH2
H|
H─C─|H
H|
H─C─|H
CH2H|
─C─|H
CH3
CH3
H|
─C─|H
CH3
CH3
H|
─C─|H
CH2 Func
t. G
rp.H
|─C─
|H
CH2 Func
t. G
rp.H
|─C─
|H
CH2 Func
t. G
rp.H
|─C─
|H
CH2 Func
t. G
rp.
Incorrect piece as an example
C3H7Cl
X-
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Example: C3H7Cl
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300 MHz ¹H NMRIn CDCl3
ALL RIGHTS RESERVED© Sigma-Aldrich Co.
H |H─C─ | H
CH2
H | ─C─ | H
CH3
CH3
H | ─C─ | H
CH2 Fun
ct.
Grp
.
X-Incorrect Match ↑
Texas Lutheran University
Example: C3H7Cl
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300 MHz ¹H NMRIn CDCl3
ALL RIGHTS RESERVED© Sigma-Aldrich Co.
H |H─C─ | H
CH2 H | ─C─ | H
CH2 Fun
ct.
Grp
.
X-Corrected Piece
Matches
H | ─C─ | H
CH2
CH3
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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
