1 H NMR Interpretation: A New Tool for Students
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Transcript of 1 H NMR Interpretation: A New Tool for Students
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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3.5 3.0 2.5 2.0 1.5 1.0
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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3.5 3.0 2.5 2.0 1.5 1.0
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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3.5 3.0 2.5 2.0 1.5 1.0
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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3.5 3.0 2.5 2.0 1.5 1.0
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
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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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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.
Texas Lutheran University
Example: C4H9Cl
0.00
0.25
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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
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Example: C4H9Cl
0.00
0.25
0.50
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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
0.00
0.25
0.50
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 | ─C─ | H
Undetermined
Splitting
H |H─C─ | H
CH
Texas Lutheran University
Example: C4H9Cl
0.00
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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 | ─C─ | H
Undetermined
Splitting
H
|
H─
C─
|
H
CH
H |H─C─ | H
CH2
Texas Lutheran University
Example: C4H9Cl
0.00
0.25
0.50
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
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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 ↑
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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
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