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Page 1: NMR Spectroscopy - NDSUcook.chem.ndsu.nodak.edu/chem342/chem342_09/files/NMRslides.pdfNMR Phenomenon ‣ Nuclear Magnetic Resonance µ A spinning charged particle generates a magnetic

NMR Spectroscopy

Tuesday, January 13, 2009

Page 2: NMR Spectroscopy - NDSUcook.chem.ndsu.nodak.edu/chem342/chem342_09/files/NMRslides.pdfNMR Phenomenon ‣ Nuclear Magnetic Resonance µ A spinning charged particle generates a magnetic

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NMR Phenomenon

‣ Nuclear Magnetic Resonance

µ A spinning charged particle generates a magnetic field.

A nucleus with a spin angular momentum will generate a magnetic moment (μ).

B0

If these tiny magnets are placed in an applied magnetic field (Bo), they will adopt two different states - one aligned with the field and one aligned against the field. The energy difference between these two states is what we are observing with NMR.

Tuesday, January 13, 2009

Page 3: NMR Spectroscopy - NDSUcook.chem.ndsu.nodak.edu/chem342/chem342_09/files/NMRslides.pdfNMR Phenomenon ‣ Nuclear Magnetic Resonance µ A spinning charged particle generates a magnetic

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Nuclear Spin States

B0

E

aligned against B0

aligned with B0

Energy difference between the states at a particular magnet strength. In the Rf range of the EM Spectrum.

When EM waves at this energy are directed at the nuclei - it will absorb. Spins will flip from lower energy to higher energy. At that energy, nuclei are “In Resonance”.

Tuesday, January 13, 2009

Page 4: NMR Spectroscopy - NDSUcook.chem.ndsu.nodak.edu/chem342/chem342_09/files/NMRslides.pdfNMR Phenomenon ‣ Nuclear Magnetic Resonance µ A spinning charged particle generates a magnetic

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NMR Active Nuclei

‣ Many nuclei are “NMR Active”

‣ Spin Quantum Number I ≠ 0

‣ 1H -- I = ½; 13C -- I = ½

‣ 12C, 16O -- I = 0 -- Can’t be observed

‣ Other nuclei that are NMR active

‣ 2H (D), 14N, 19F, 31P

Tuesday, January 13, 2009

Page 5: NMR Spectroscopy - NDSUcook.chem.ndsu.nodak.edu/chem342/chem342_09/files/NMRslides.pdfNMR Phenomenon ‣ Nuclear Magnetic Resonance µ A spinning charged particle generates a magnetic

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NMR Instrumentation

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Page 6: NMR Spectroscopy - NDSUcook.chem.ndsu.nodak.edu/chem342/chem342_09/files/NMRslides.pdfNMR Phenomenon ‣ Nuclear Magnetic Resonance µ A spinning charged particle generates a magnetic

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Magnetic Resonance Imaging

‣ NMR is the basis for MRI

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Page 7: NMR Spectroscopy - NDSUcook.chem.ndsu.nodak.edu/chem342/chem342_09/files/NMRslides.pdfNMR Phenomenon ‣ Nuclear Magnetic Resonance µ A spinning charged particle generates a magnetic

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To summarize

µ

B0

A spinning charged particle generates a magnetic field.A nucleus with a spin angular momentum will generate a magnetic moment (m).

When placed in a magnetic field (Bo), they will adopt two different states - one aligned with the field and one aligned against the field.

B0

E

aligned against B0

aligned with B0

Energy difference between the states at a particular magnet strength. In the Rf range of the EM Spectrum.

Tuesday, January 13, 2009

Page 8: NMR Spectroscopy - NDSUcook.chem.ndsu.nodak.edu/chem342/chem342_09/files/NMRslides.pdfNMR Phenomenon ‣ Nuclear Magnetic Resonance µ A spinning charged particle generates a magnetic

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Methyl Acetate - Proton NMR

H3CC

OCH3

O

Tuesday, January 13, 2009

Page 9: NMR Spectroscopy - NDSUcook.chem.ndsu.nodak.edu/chem342/chem342_09/files/NMRslides.pdfNMR Phenomenon ‣ Nuclear Magnetic Resonance µ A spinning charged particle generates a magnetic

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Methyl Acetate - Carbon NMR

H3CC

OCH3

O

solvent

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Page 10: NMR Spectroscopy - NDSUcook.chem.ndsu.nodak.edu/chem342/chem342_09/files/NMRslides.pdfNMR Phenomenon ‣ Nuclear Magnetic Resonance µ A spinning charged particle generates a magnetic

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Electronic Shielding - Local Environments

µ

B0 Beffective

Blocal

Beffective = B0 - Blocal

Actual magnetic field felt by the nucleus

Tuesday, January 13, 2009

Page 11: NMR Spectroscopy - NDSUcook.chem.ndsu.nodak.edu/chem342/chem342_09/files/NMRslides.pdfNMR Phenomenon ‣ Nuclear Magnetic Resonance µ A spinning charged particle generates a magnetic

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Methyl Acetate - Proton NMR

H3CC

OCH3

O

Tuesday, January 13, 2009

Page 12: NMR Spectroscopy - NDSUcook.chem.ndsu.nodak.edu/chem342/chem342_09/files/NMRslides.pdfNMR Phenomenon ‣ Nuclear Magnetic Resonance µ A spinning charged particle generates a magnetic

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Methyl Acetate - Carbon NMR

H3CC

OCH3

O

solvent

CO

Tuesday, January 13, 2009

Page 13: NMR Spectroscopy - NDSUcook.chem.ndsu.nodak.edu/chem342/chem342_09/files/NMRslides.pdfNMR Phenomenon ‣ Nuclear Magnetic Resonance µ A spinning charged particle generates a magnetic

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Chemical Shift

‣ The difference in resonance frequency of a nuclei relative to a standard

‣ Most Shielded

‣ Relatively Inert

‣ Volatile

‣ Resonance of standard is set to 0

Si CH3

CH3H3C

CH3TMS

TetraMethylSilane

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Page 14: NMR Spectroscopy - NDSUcook.chem.ndsu.nodak.edu/chem342/chem342_09/files/NMRslides.pdfNMR Phenomenon ‣ Nuclear Magnetic Resonance µ A spinning charged particle generates a magnetic

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NMR Scale

0

Low FieldLittle electron shielding(more electron withdrawing groups)

High FieldMore electron shielding

(less electron withdrawing groups)

NMR Spectrum

ReferenceTMS

peaks measured as a shift (in Hz) away from TMS

10 Hz

‣ X-Axis - frequency axis

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Page 15: NMR Spectroscopy - NDSUcook.chem.ndsu.nodak.edu/chem342/chem342_09/files/NMRslides.pdfNMR Phenomenon ‣ Nuclear Magnetic Resonance µ A spinning charged particle generates a magnetic

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Different Spectrometer Frequencies

‣ Each specific instrument has it’s own magnetic field strength - resonace occurs at different frequencies.

0100 Hz300 Hz

100 MHz NMR300 MHz NMR

ReferenceTMS

B0

E

aligned against B0

aligned with B0

Energy difference between the states at a particular magnet strength. In the Rf range of the EM Spectrum.

Tuesday, January 13, 2009

Page 16: NMR Spectroscopy - NDSUcook.chem.ndsu.nodak.edu/chem342/chem342_09/files/NMRslides.pdfNMR Phenomenon ‣ Nuclear Magnetic Resonance µ A spinning charged particle generates a magnetic

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Standard Scale

‣ δ = ppm = Chemical Shift from TMS (Hz)Spectrometer Frequency (MHz)

0

100 MHz NMR300 MHz NMR

1.0 ppm

ReferenceTMS

100 Hz100 MHz

= 1.0 ppm

300 Hz300 MHz

= 1.0 ppm

Tuesday, January 13, 2009

Page 17: NMR Spectroscopy - NDSUcook.chem.ndsu.nodak.edu/chem342/chem342_09/files/NMRslides.pdfNMR Phenomenon ‣ Nuclear Magnetic Resonance µ A spinning charged particle generates a magnetic

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NMR Scale

Tuesday, January 13, 2009

Page 18: NMR Spectroscopy - NDSUcook.chem.ndsu.nodak.edu/chem342/chem342_09/files/NMRslides.pdfNMR Phenomenon ‣ Nuclear Magnetic Resonance µ A spinning charged particle generates a magnetic

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C13 NMR

‣ Difficult - Carbon 13 only 1.1% of all carbon.

‣ Number of different carbons

‣ Functional Group Regions

200

CC C

CO

RR

13C NMR

150 100 50 0δ ppm

C O C N C X

CO

ORR

CO

NR2R

Tuesday, January 13, 2009

Page 19: NMR Spectroscopy - NDSUcook.chem.ndsu.nodak.edu/chem342/chem342_09/files/NMRslides.pdfNMR Phenomenon ‣ Nuclear Magnetic Resonance µ A spinning charged particle generates a magnetic

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C13 NMR

OH

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Page 20: NMR Spectroscopy - NDSUcook.chem.ndsu.nodak.edu/chem342/chem342_09/files/NMRslides.pdfNMR Phenomenon ‣ Nuclear Magnetic Resonance µ A spinning charged particle generates a magnetic

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Symmetry

‣ Symmetry in molecules can make carbons “Chemically Equivalent”

H3CC

CH3

O

same electronic

environment

Cl

Br

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Page 21: NMR Spectroscopy - NDSUcook.chem.ndsu.nodak.edu/chem342/chem342_09/files/NMRslides.pdfNMR Phenomenon ‣ Nuclear Magnetic Resonance µ A spinning charged particle generates a magnetic

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Symmetry

‣ Some molecules have more than one mirror plane

CH3

CH3

CH3

CH3

Tuesday, January 13, 2009

Page 22: NMR Spectroscopy - NDSUcook.chem.ndsu.nodak.edu/chem342/chem342_09/files/NMRslides.pdfNMR Phenomenon ‣ Nuclear Magnetic Resonance µ A spinning charged particle generates a magnetic

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Symmetry

CH3

CH3

CH3

CH3

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Page 23: NMR Spectroscopy - NDSUcook.chem.ndsu.nodak.edu/chem342/chem342_09/files/NMRslides.pdfNMR Phenomenon ‣ Nuclear Magnetic Resonance µ A spinning charged particle generates a magnetic

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Symmetry

CH3CH3

CH3

CH3

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Page 24: NMR Spectroscopy - NDSUcook.chem.ndsu.nodak.edu/chem342/chem342_09/files/NMRslides.pdfNMR Phenomenon ‣ Nuclear Magnetic Resonance µ A spinning charged particle generates a magnetic

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Substitution of Carbon

‣ The intensity of the peaks roughly correlates with the number of hydrogens on the carbon.

Tuesday, January 13, 2009

Page 25: NMR Spectroscopy - NDSUcook.chem.ndsu.nodak.edu/chem342/chem342_09/files/NMRslides.pdfNMR Phenomenon ‣ Nuclear Magnetic Resonance µ A spinning charged particle generates a magnetic

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C13 NMR Regions

200

CC C

CO

RR

13C NMR

150 100 50 0δ ppm

C O C N C X

CO

ORR

CO

NR2R

Tuesday, January 13, 2009

Page 26: NMR Spectroscopy - NDSUcook.chem.ndsu.nodak.edu/chem342/chem342_09/files/NMRslides.pdfNMR Phenomenon ‣ Nuclear Magnetic Resonance µ A spinning charged particle generates a magnetic

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Bromooctanol

HOBr

Tuesday, January 13, 2009

Page 27: NMR Spectroscopy - NDSUcook.chem.ndsu.nodak.edu/chem342/chem342_09/files/NMRslides.pdfNMR Phenomenon ‣ Nuclear Magnetic Resonance µ A spinning charged particle generates a magnetic

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Bromooctanal

OBr

H

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Page 28: NMR Spectroscopy - NDSUcook.chem.ndsu.nodak.edu/chem342/chem342_09/files/NMRslides.pdfNMR Phenomenon ‣ Nuclear Magnetic Resonance µ A spinning charged particle generates a magnetic

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Alanine Me-Ester HCl

H3C NH3Cl

O OCH3

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Page 29: NMR Spectroscopy - NDSUcook.chem.ndsu.nodak.edu/chem342/chem342_09/files/NMRslides.pdfNMR Phenomenon ‣ Nuclear Magnetic Resonance µ A spinning charged particle generates a magnetic

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Alaninol

H3C NH2

OH

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Alaninol - phthalimide

H3C N

OH

O

O

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Page 31: NMR Spectroscopy - NDSUcook.chem.ndsu.nodak.edu/chem342/chem342_09/files/NMRslides.pdfNMR Phenomenon ‣ Nuclear Magnetic Resonance µ A spinning charged particle generates a magnetic

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DEPT-C13

‣ A - normal C13

‣ B - CH carbons only

‣ C - Odd # up (CH3 and CH) Even # down (CH2)

OH

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Page 32: NMR Spectroscopy - NDSUcook.chem.ndsu.nodak.edu/chem342/chem342_09/files/NMRslides.pdfNMR Phenomenon ‣ Nuclear Magnetic Resonance µ A spinning charged particle generates a magnetic

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Example from 13.7

ClKOHethanol or

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Page 33: NMR Spectroscopy - NDSUcook.chem.ndsu.nodak.edu/chem342/chem342_09/files/NMRslides.pdfNMR Phenomenon ‣ Nuclear Magnetic Resonance µ A spinning charged particle generates a magnetic

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A Real Example

NH

NO O

O

NH

NO O

O

NH

O

N

O

O

OR

H2, Pd/C

NH

NO O

O

H2, Pd/C

NH

NO O

O

NH

O

N

O

O

OR

In the alkane regionthere would only be 4 peaks due to symmetry

In the alkane regionthere would be 6 different peaks

Tuesday, January 13, 2009

Page 34: NMR Spectroscopy - NDSUcook.chem.ndsu.nodak.edu/chem342/chem342_09/files/NMRslides.pdfNMR Phenomenon ‣ Nuclear Magnetic Resonance µ A spinning charged particle generates a magnetic

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The Answer Is . . .

NH

NO O

O

NH

O

N

O

O

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Page 35: NMR Spectroscopy - NDSUcook.chem.ndsu.nodak.edu/chem342/chem342_09/files/NMRslides.pdfNMR Phenomenon ‣ Nuclear Magnetic Resonance µ A spinning charged particle generates a magnetic

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Proton NMR

‣ Number of chemically different hydrogens

‣ Relative Ratios of protons (peak size)

‣ How many neighboring hydrogens

‣ Chemical shifts and functional groups

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Page 36: NMR Spectroscopy - NDSUcook.chem.ndsu.nodak.edu/chem342/chem342_09/files/NMRslides.pdfNMR Phenomenon ‣ Nuclear Magnetic Resonance µ A spinning charged particle generates a magnetic

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Proton Equivalency

Homotopic

Enantiotopic

Diastereotopic

H3CC

CH3

H H

replace H's - same

H3CC

CH3

H X

H3CC

CH3

X HH3C

CCH2

CH3

H H

replace H's - enantiomers

H3CC

CH2

CH3

X H

H3CC

CH2

CH3

H X

H3CC

CCH3

H H

replace H's - diastereomers

H3CC

CCH3

X H

H3CC

CCH3

H X

H Cl

Cl ClH H

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Proton NMR Scale

‣ Range 0-10 ppm

10

CH

H H

HH

4 1 0δ ppm

C X

5 239 678

HH

HH

H

H

H

CCH

C OH

C OOH

1H NMR

Tuesday, January 13, 2009

Page 38: NMR Spectroscopy - NDSUcook.chem.ndsu.nodak.edu/chem342/chem342_09/files/NMRslides.pdfNMR Phenomenon ‣ Nuclear Magnetic Resonance µ A spinning charged particle generates a magnetic

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NMR Correlation Chart

C H

C C

O H

Functional Group

Type 1H Chemical Shift (ppm)

Alkane

Allylic or next to carbonyl 1.6 - 2.4

alcohol varies widelywill exchange with D2O

Typical NMR Chemical Shifts

0.7 -1.8

H

CX Hnext to

halogen or alcohol

2.5 - 4.0

CO Hnext to

oxygen of an ester

4.0 - 5.0CO

C Hvinylic 4.5 - 6.5

CH

aromatic 6.5 - 8.0

C HO

aldehyde 9.7 - 10.0

C XO

carbonyl of ester, amide, or carboxylic acid

(X = O, N)165 - 185

CO carbonyl of

ketone or aldehyde

190 - 220

30 - 60

10 - 60

20 - 85

50 - 85

110 - 150

110 - 140

190 - 220

13C Chemical Shift (ppm)

N/A

N/A

N/A

Tuesday, January 13, 2009

Page 39: NMR Spectroscopy - NDSUcook.chem.ndsu.nodak.edu/chem342/chem342_09/files/NMRslides.pdfNMR Phenomenon ‣ Nuclear Magnetic Resonance µ A spinning charged particle generates a magnetic

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Methyl Acetate

H3CC

OCH3

O

Area under peak corresponds to the number of H’s for that resonance

Tuesday, January 13, 2009

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Triphenyl Methanol

OH

Tuesday, January 13, 2009

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Ethyl Acetate

H3CC

O

H2C

O

CH3

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‣ Protons on adjacent carbons also have an effect

‣ Resonances will split into n+1 number of peaks

Spin Spin Splitting

C CHa Hb

Hb

1H NMR (without coupling)

1H NMR (with coupling)

Ha Hb

J J

Tuesday, January 13, 2009

Page 43: NMR Spectroscopy - NDSUcook.chem.ndsu.nodak.edu/chem342/chem342_09/files/NMRslides.pdfNMR Phenomenon ‣ Nuclear Magnetic Resonance µ A spinning charged particle generates a magnetic

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Spin Spin Splitting

‣ Two hydrogens split neighbors into a triplet

C C Hb

Ha Hb

Hb

1H NMR (without coupling)

1H NMR (with coupling)

Ha Hb

J JJ

1 11 : 2 1:

Tuesday, January 13, 2009

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Spin Spin Splitting

‣ Every splitting can be broken down into a series of doublets 1H NMR

(without coupling)

1H NMR (with coupling)

Ha

J

1 11 : 2 1:

J J

1 1

C C Hb

Ha Hb

Hb

Tuesday, January 13, 2009

Page 45: NMR Spectroscopy - NDSUcook.chem.ndsu.nodak.edu/chem342/chem342_09/files/NMRslides.pdfNMR Phenomenon ‣ Nuclear Magnetic Resonance µ A spinning charged particle generates a magnetic

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Spin Spin Splitting

‣ Three neighbors - Quartet

C CHb

Hb

Ha Hb

Hb

1 11 : 3 3:

1H NMR (without coupling)

1H NMR (with coupling)

Ha Hb

JJ

JJ

11:

Tuesday, January 13, 2009

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Higher Spin Spin Splitting

singlet 11 1doublet

1 2 1triplet1 3 3 1quartet

1 4 6 4 11 5 10 10 5 1

1 6 15 20 15 6 1

quintetsextetseptet

C CHb

Hb

Ha Hb

CHb

Hb

Hb

Ha will split into 7 peaks

Pascal’s Triangle

64 different combinations

of 6 spins

Tuesday, January 13, 2009

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Summary of Spin Spin Splitting

‣ Proton resonance split into n+1 number of peaks

‣ Relative ratio of peaks depends on number of spin states of the neighbors.

‣ Adjacent protons will couple with the same coupling constant.

‣ Protons farther away usually do not couple.

‣ Chemically equivalent protons cannot couple (eg. ClCH2CH2Cl).

Tuesday, January 13, 2009

Page 48: NMR Spectroscopy - NDSUcook.chem.ndsu.nodak.edu/chem342/chem342_09/files/NMRslides.pdfNMR Phenomenon ‣ Nuclear Magnetic Resonance µ A spinning charged particle generates a magnetic

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Doublet Splitting

Methyl sees 1 neighbor, Methine sees 3

CH3C NH3Cl

CO O

CH3

H

Tuesday, January 13, 2009

Page 49: NMR Spectroscopy - NDSUcook.chem.ndsu.nodak.edu/chem342/chem342_09/files/NMRslides.pdfNMR Phenomenon ‣ Nuclear Magnetic Resonance µ A spinning charged particle generates a magnetic

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Ethanol

‣ Note that the OH (and NH) usually don’t couple.

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1,1,2-Trichloroethane

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2-Bromopropane

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Butanone

O

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para-Methoxypropiophenone

Tuesday, January 13, 2009

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Toluene

‣ Sometimes peaks overlap

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Cinnamaldehyde

‣ Multiple Coupling

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Spin Spin Splitting

‣ Every splitting can be broken down into a series of doublets 1H NMR

(without coupling)

1H NMR (with coupling)

Ha

J

1 11 : 2 1:

J J

1 1

C C Hb

Ha Hb

Hb

Tuesday, January 13, 2009

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Coupling with the same J

C CHa Hc

Ja-b = 5 Hz

CHb

Ja-c = 5 Hz

Ha

coupling with Hb5

1 2 1

5 5coupling with Hc

Tuesday, January 13, 2009

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Coupling with different J values

C CHa Hc

Ja-b = 5 Hz

CHb

Ja-c = 10 Hz

Ha

1 1

coupling with Hb5

10coupling with Hc1 1

10

Ha

1 1

coupling with Hb

coupling with Hc

1 1

10

5 5

Tuesday, January 13, 2009

Page 59: NMR Spectroscopy - NDSUcook.chem.ndsu.nodak.edu/chem342/chem342_09/files/NMRslides.pdfNMR Phenomenon ‣ Nuclear Magnetic Resonance µ A spinning charged particle generates a magnetic

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Cinnamaldehyde

‣ Multiple Coupling

‣ J H1-H2 = 6 Hz, H2-H3 = 12 Hz

Tuesday, January 13, 2009

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Cinnemaldehyde

Tuesday, January 13, 2009

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Multiple Coupling - Identical J

Ha

coupling with Hb5

1 2 15 5

coupling with Hc

coupling with Hc1 3 3

5 5

1

5

C C Hc

Ha Hc

C

Hb

Ja-b = 5 Hz Ja-c = 5 Hz

Tuesday, January 13, 2009

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Multiple Coupling - Different J

C C Hc

Ha Hc

C

Hb

Ja-b = 10 Hz Ja-c = 5 Hz Ha

coupling with Hb2 2

10

1 2 1

coupling with Hc5

5 5coupling with Hc

1

10

21

10

Tuesday, January 13, 2009

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Nitropropane

Tuesday, January 13, 2009

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Strategies for Determining Unknows

‣ Given the Molecular Formula - calculate degrees of unsaturation.

‣ Identify functional groups

‣ Identify pieces of the structure

‣ Put the pieces together in a reasonable way

‣ Double check that your structure matches all the data given.

Tuesday, January 13, 2009