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13C-NMR
SPECTROSCOPY
With examples
by
DR ANTHONY MELVIN CRASTO
Principal Scientist
INDIA
FEB 2016
THIS IS A VAST TOPIC AND A SHORT
OVERVIEW IS GIVEN
AND
IN NO WAY COMPLETE JUSTICE CAN BE
DONE FOR THIS
DEFINITION
 NMR is a phenomenon exhibited by when
atomic nuclei in a static magnetic field absorbs
energy from radiofrequ...
NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY
 Proton (1H) and carbon (13C) are the most important nuclear
spins to organic che...
NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY
 Some nuclear spins are aligned parallel to the external field
 Lower energy ori...
INTRODUCTION
 Nuclear magnetic resonance concern the magnetic properties of
certain atomic nuclei. It concerns the atoms ...
PRINCIPLE & THEORY
 The nuclear magnetic resonance occurs when nuclei aligned with
an applied field are induced to absorb...
PRINCIPLE OF NMR
When energy in the form of radiofrequency is applied
When applied frequency is equal to precessional
freq...
NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY
Many nuclei exhibit NMR phenomenon
 All nuclei with odd number
of protons
 All n...
ABUNDANCE
13C is difficult to record because of
1. The most abundant isotope of carbon that is
12C (99.1%) is not detected...
Advantages of 13C- NMR over 1H- NMR
1. 13C- provides information about the backbone of
molecules rather than the periphery...
SPIN –SPIN SPLITTING OF 13C
SIGNALS
 Splitting take place acc. to 2nI+1 rule
Where n= no. of nuclei
I=spin quantum number...
13C chemical shifts
The most significant factors affecting the chemical shifts are:
Electro negativity of the groups attac...
Why Carbon-13 NMR required?
 Carbon NMR can used to determine the number of non-equivalent
carbons and to identify the ty...
WHY 13C NMR REQUIRED ??
 Proton NMR used for study of number of nonequivalent
proton present in unknown compound.
 Carbo...
CHARACTERISTIC FEATURES OF 13C NMR
• The chemical shift of the CMR is wider(δ is 0-220 ppm relative to TMS) in
comparison ...
CHARACTERISTIC FEATURES OF 13C NMR
 The area under the peak in CMR spectrum is not necessary
to be proportional to the nu...
13C CHEMICAL SHIFTS
are measured in ppm (d) from the carbons of TMS
• The correlation chart is here divided into sections
...
13C INTERPRETATION
 Count how many lines- how many types of carbons
 Symmetry duplicates give same line- if there are mo...
13C INTERPRETATION
13C NMR spectroscopy provides information
about:
 The number of nonequivalent carbons atoms in
a molec...
EXAMPLE
PREDICTING CHEMICAL SHIFTS IN 13C NMR SPECTRA
Solution
 Ethyl acrylate has five distinct carbons: two different C...
CHEMICAL SHIFT
Carbon-13 chemical shifts are most affected by,
 Hybridiasation state of carbon & Electronegative group at...
CORRELATION CHART
CHEMICAL SHIFT
020406080100120140160180200220
PPM
0246810
PPM
1H NMR
13C NMR
1H range = 0 to
~ 12 ppm
13C range = 0 to
~ 2...
1H AND 13C NMR COMPARED
13C signals are spread over a much wider range than 1H
signals making it easier to identify and co...
1-CHLOROPENTANE
01.02.03.04.05.06.07.08.09.010.0
Chemical shift (d, ppm)
ClCH2 CH3
ClCH2CH2CH2CH2CH3
1H
1-CHLOROPENTANE
Chemical shift (d, ppm)
ClCH2CH2CH2CH2CH3
020406080100120140160180200
13C
CDCl3
a separate, distinct
peak ...
13C CHEMICAL SHIFTS ARE MOST AFFECTED BY
 hybridization state of carbon-
 electronegativity of groups attached to
carbon...
PREDICTING 13C SPECTRA
CH3 CH3
C C
C
C
C
CH3
plane of symmetry
4 lines
O
CH3
CH3
O
CH3
CH3
C
C
c
CH3
O
CH3 5 lines
CH3
C
C...
PREDICTING 13C SPECTRA
CH3
CH3
H3C CH3
C C
C
CC
C
H3C CH3
4 lines
C C
CH3
CH3
CH3
CH3
C C
CH3
CH3
CH3
CH3
2 lines
Symmetry...
C
O CDCl3 (solvent)
CH3CCH3
O
CH3
C
O
CH3COCH2CH3
O
OCH2
CH3
CDCl3 (solvent)
PROBLEMS OF 13
C
• Natural abundance-
13
C natural abundance is very low (1.1%).
 Gyro magnetic ratio-
13
C nucleus gyro ...
PROBLEMS IN NMR CAN BE OVERCOME BY
 Fourier Transform Technique-
 Decoupling Technique-
1) Broad Band Decoupling
2) Off ...
SIGNAL AVERAGING AND FT-NMR
 Low abundance of 13C is overcome by signal averaging and
Fourier-transform NMR (FT-NMR)
 Si...
SIGNAL AVERAGING AND FT-NMR
FT-NMR: (Pulse FT_NMR)
 Sample is irradiated with entire range of useful frequencies
 13C nu...
Carbon-13 NMR spectra of pentan-1-ol. Spectrum (a) is a single run,
showing background noise. Spectrum (b) is an average o...
13
C-NMR SPIN-SPIN COUPLING

1
H NMR: Splitting reveals number of H neighbours.
13
C NMR: Limited to nuclei separated by ...
DECOUPLING TECHNIQUES
• Irradiation of all 1H nuclei by using
decoupler
• 1H nuclei are saturated & C nuclei see
zero coup...
PROTON OR BROADBAND DECOUPLING
a sample is irradiated with two different radiofrequencies.
,
These rapid transition decoup...
Proton Decoupling
Three types:
1. Broad band decoupling
2. Off-resonance decoupling
3. Pulse decoupling
Proton-coupled 13C splitting patterns
Broad band decoupling
1. It avoid spin-spin splitting of 13C lines by 1H
nuclei.
2. In this, all the protons are simultane...
13C OFF-RESONANCE DECOUPLING
 In this technique the 13C nuclei are split only by the protons
directly bonded to them as a...
13C OFF-RESONANCE DECOUPLED SPECTRUM
3 protons
n+1=4
2 protons
n+1=3
1 proton
n+1=2
0 protons
n+1=1
Methyl ‘C’ Methylene ‘...
OFF-RESONANCE DECOUPLING
 Off-Resonance decoupling simplifies the spectrum by
allowing some of the splitting information ...
EXAMPLE: PROPANOL
13C OFF-RESONANCE DECOUPLED SPECTRUM
1,2,2-trichloropropane
P.S.Kalsi; Spectroscopy Of Organic Compounds, Sixth Edition:20...
Nuclear Overhauser Enhancement (NOE)
A. Under conditions of broad band decoupling it found that the area of the 13C
peaks ...
THEORY OF NOE
Consider a hypothetical
molecule in which 2 protons
are in close proximity . In such
compound, if we double
...
Off-resonance decoupling
1. The coupling between each carbon atom and each hydrogen
attached directly to it, s observed ac...
HYDROGEN DECOUPLED
MODE(BROAD BAND DECOUPLED)
 A sample is irradiated with two different radio frequencies.
 One to exci...
ETHYL PHENYLACETATE
13C coupled
to the hydrogens
13C decoupled
from the hydrogens
-CH3
A
3+1=4
AB C
B
2+1=3
-CH2
C, 2+1=3
...
WHY DECOUPLE 13 C NMR
MESSY SPECTRUM
SIMPLE
25 MHz 13C NMR spectra of diphenyl selenide in CDCl3.
Figure shows the fully coupled and decoupled 13C NMR spectra of diph...
Most 13C NMR spectra are very complex. The methyl carbon of an
ethoxy group will appear as a large quartet, with each line...
DEPT 13C NMR Spectroscopy
Distortionless Enhancement by Polarization Transfer (DEPT-NMR)
experiment
• Run in three stages
...
Attached proton test spectra
Another useful way of determining how many protons a
carbon in a molecule is bonded to is to ...
Spectral Editing
There are a number of multipulse experiments which render the signals
in a 13C NMR spectrum with positive...
DEPT 13C NMR Spectroscopy
DEPT 45 ALL H BEARING PEAKS
DEPT 13C NMR Spectroscopy
(a) Ordinary broadband-decoupled
spectrum showing signals for all
eight of 6-methylhept-5-en-2-o...
EXAMPLE: 6METHYLHEPT-5-EN-2-
OL
DEPT
135
DEPT 90
Ordinary broadband-
decoupled spectrum
DEPT spectra of isopentyl acetate
CH3, CH
CH2
CH
DEPT spectra of isopentyl acetate
DEPT 45 ALL H BEARING PEAKS
POSITIVE
COSY SPECTRUM
 2D NMR spectra have two frequency axes and one intensity
 The common 2D spectra are 1 H -1H shift correla...
COSY SPECTRUM OF M-
DINITROBENZENE
HECTOR SPECTRUM
 2D-NMR spectra that displays 13C – 1H-NMR shift correlations are called HETCOR
spectra. It shows couplin...
THE HETCOR SPECTRUM OF 2-METHYL-3-PENTANONE
HETCOR: Heteronuclear Chemical Shift Correlation
indicates coupling between pr...
APPLICATIONS OF 13C NMR
 CMR is a noninvasive and nondestructive
method,i.e,especially used in repetitive In-vivo analysi...
Application’s
• C-13 enrichment, which the signal intensities and helps in tracing
the cellular metabolism.
• C13 nuclei a...
EXAMPLES
Lead points before going to examples
-COOH
-COCH3
-CH3
The off-resonance proton-decoupled 13C NMR spectrum for ethyl
phenylacetate
102
S
N
N
S
NH
CH3
O
NH2
CH3
3c
Molecular Formula: C14H16N4OS2
C=O
CH3
CH
13C NMR spectrum of 2-(Alanyl)-Amino-5-(4-methyl...
103
S
N
N
S
N
O
Cl
H3C
4d
Molecular Formula = C20H16ClN3OS2
C=O
CH3
CH-Cl
CH
13C NMR spectrum of 3-chloro-1-[5-(4-methylph...
<
>
INEPT =Insensitive nuclei enhanced by
polarization transfer
Example : 13C-NMR spectrum of diethyl phthalate
INTERPRETED
SPECTRUM
JUST A VISUAL EXAMPLE
JUST A VISUAL EXAMPLE
DEPT spectrum of isobutyl acetate
d (ppm) type of signal in DEPT represent
22 (b) positive 2 CH3
24 (c) positive CH3
24 (a) positive CH
37 (d) negative CH2
...
DEPT spectrum of caryophyllene oxide
CH ONLY
C
O
=CH2
C
O
C-C-C
I-CH3
C-C-C
C
O
C
O
C-C-C
CDCl3 (solvent)
C-C-C
C-C-C
CDCl3 (solvent)
C-
Br
C-C-C
CDCl3 (solvent)C-0
N-C-C
OCH2
C-0
C
O
C-C-C
CDCl3 (solvent)
C=C
C=C
The 13C NMR (APT, 50 MHz, DMSO-d6) study of the compound MIC-14
showed thirteen chemical shifts. Of these, seven were assi...
For compound MIC-16 we observed a similar chemical behavior.
The 13C NMR (APT, 50 MHz, DMSO-d6) spectrum showed thirteen s...
13 CNMR (DMSO, 75MHz) :δ 23.5, 82.1, 118.3, 122.2, 126.5, 126.9, 142.1, 167.4,
187.8 ppm.
Teriflunomide,
LIONEL MY SON
He was only in first standard in school when I was hit by a
deadly one in a million spine stroke called acut...
MY BLOGS
ORGANIC SPECTROSCOPY INTERNATIONAL
LINK….. http://orgspectroscopyint.blogspot.in/
ORGANIC SPECTROSCOPY INTERNATIO...
To take full advantage of Chemical Web content, it is essential
to use several Software:Winzip,Chemscape Chime, Shockwave,...
SUCCESS FORMULA
13 C NMR Spectroscopy with examples by Dr Anthony Crasto
13 C NMR Spectroscopy with examples by Dr Anthony Crasto
13 C NMR Spectroscopy with examples by Dr Anthony Crasto
13 C NMR Spectroscopy with examples by Dr Anthony Crasto
13 C NMR Spectroscopy with examples by Dr Anthony Crasto
13 C NMR Spectroscopy with examples by Dr Anthony Crasto
13 C NMR Spectroscopy with examples by Dr Anthony Crasto
13 C NMR Spectroscopy with examples by Dr Anthony Crasto
13 C NMR Spectroscopy with examples by Dr Anthony Crasto
13 C NMR Spectroscopy with examples by Dr Anthony Crasto
13 C NMR Spectroscopy with examples by Dr Anthony Crasto
13 C NMR Spectroscopy with examples by Dr Anthony Crasto
13 C NMR Spectroscopy with examples by Dr Anthony Crasto
13 C NMR Spectroscopy with examples by Dr Anthony Crasto
13 C NMR Spectroscopy with examples by Dr Anthony Crasto
13 C NMR Spectroscopy with examples by Dr Anthony Crasto
13 C NMR Spectroscopy with examples by Dr Anthony Crasto
13 C NMR Spectroscopy with examples by Dr Anthony Crasto
13 C NMR Spectroscopy with examples by Dr Anthony Crasto
13 C NMR Spectroscopy with examples by Dr Anthony Crasto
13 C NMR Spectroscopy with examples by Dr Anthony Crasto
13 C NMR Spectroscopy with examples by Dr Anthony Crasto
13 C NMR Spectroscopy with examples by Dr Anthony Crasto
13 C NMR Spectroscopy with examples by Dr Anthony Crasto
13 C NMR Spectroscopy with examples by Dr Anthony Crasto
13 C NMR Spectroscopy with examples by Dr Anthony Crasto
13 C NMR Spectroscopy with examples by Dr Anthony Crasto
13 C NMR Spectroscopy with examples by Dr Anthony Crasto
13 C NMR Spectroscopy with examples by Dr Anthony Crasto
13 C NMR Spectroscopy with examples by Dr Anthony Crasto
13 C NMR Spectroscopy with examples by Dr Anthony Crasto
13 C NMR Spectroscopy with examples by Dr Anthony Crasto
13 C NMR Spectroscopy with examples by Dr Anthony Crasto
13 C NMR Spectroscopy with examples by Dr Anthony Crasto
13 C NMR Spectroscopy with examples by Dr Anthony Crasto
13 C NMR Spectroscopy with examples by Dr Anthony Crasto
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13 C NMR Spectroscopy with examples by Dr Anthony Crasto

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13 C NMR Spectroscopy with examples by Dr Anthony Crasto

  1. 1. 13C-NMR SPECTROSCOPY With examples by DR ANTHONY MELVIN CRASTO Principal Scientist INDIA FEB 2016
  2. 2. THIS IS A VAST TOPIC AND A SHORT OVERVIEW IS GIVEN AND IN NO WAY COMPLETE JUSTICE CAN BE DONE FOR THIS
  3. 3. DEFINITION  NMR is a phenomenon exhibited by when atomic nuclei in a static magnetic field absorbs energy from radiofrequency field of certain characteristic frequency.  It results to give a spectrum with frequency on x- axis and intensity of absorption on y-axis.
  4. 4. NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY  Proton (1H) and carbon (13C) are the most important nuclear spins to organic chemists  Nuclear spins are oriented randomly= absence (a) of an external magnetic field.  specific orientation= presence (b) of an external field, B0 Pavia, Lampman, Kriz, Vyvyan; Spectroscopy, Cengage Learning, India edition, 2007, Pg. no. 108
  5. 5. NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY  Some nuclear spins are aligned parallel to the external field  Lower energy orientation  Some nuclear spins are aligned antiparallel to the external field  Higher energy orientation P.S.Kalsi; Spectroscopy Of Organic Compounds, Sixth Edition:2004, Page no.-195
  6. 6. INTRODUCTION  Nuclear magnetic resonance concern the magnetic properties of certain atomic nuclei. It concerns the atoms having spin quantum number.  12C nucleus is not magnetically active the spin number I being zero. But 13C Have I = ½  13C account for only 1.1% of naturally occurring carbon 13C- 13C coupling is negligible and not observed.  The gyromagnetic ratio of 13C is one-fourth of that of 1H.  Each nonequivalent 13C gives a different signal.  A 13C signal is split by the 1H bonded to it according to the (n + 1) rule.  The most common mode of operation of a 13C-NMR spectrometer is a hydrogen-decoupled mode.
  7. 7. PRINCIPLE & THEORY  The nuclear magnetic resonance occurs when nuclei aligned with an applied field are induced to absorb energy and change their spin orientation with respect to the applied field.  The energy absorption is a quantized process, and energy absorbed must equal the energy difference between the two states involved. E absorbed = (E-1/2state- E+1/2state) =hv  The stronger the applied magnetic field, greater the energy difference between the possible spin states. ΔE = ∫(B0)
  8. 8. PRINCIPLE OF NMR When energy in the form of radiofrequency is applied When applied frequency is equal to precessional frequency. Absorption of energy occures Nucleus is in resonance NMR signal is recorded. Pavia, Lampman, Kriz, Vyvyan; Spectroscopy, Cengage Learning, India edition, 2007, Pg. no. 108
  9. 9. NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY Many nuclei exhibit NMR phenomenon  All nuclei with odd number of protons  All nuclei with odd number of neutrons  Nuclei with even numbers of both protons and neutrons do not exhibit NMR phenomenon Table-1
  10. 10. ABUNDANCE 13C is difficult to record because of 1. The most abundant isotope of carbon that is 12C (99.1%) is not detected by nmr because it has an even no of protons and neutrons 12C is nmr inactive. 2. Magnetic resonance of 13C is much weaker. Moreover, gyromagnectic ratio of 13C being only one fourth that of proton, so the resonance frequency of 13C is one fourth that of proton nmr.
  11. 11. Advantages of 13C- NMR over 1H- NMR 1. 13C- provides information about the backbone of molecules rather than the periphery. 2. The chemical shifts range for 13C- NMR for most organic compounds is 200 ppm compared to 10 –15 ppm for H, hence there is less overlap of peaks for 13C- NMR. 3. Homonuclear spin-spin coupling between carbon atoms is not observed because the natural abundance of 13C is too low for two 13C to be next to one another. Heteronuclear spin coupling between 13C and 12C does not occur because the spin quantum number of 12C is zero. 4. There are a number of excellent methods for decoupling the interaction between 13 C and 1H.
  12. 12. SPIN –SPIN SPLITTING OF 13C SIGNALS  Splitting take place acc. to 2nI+1 rule Where n= no. of nuclei I=spin quantum number CH3 = 3+1=4 quartet CH2 = 2+1=3 triplet CH = 1+1=2 doublet C = 0+1=1 singlet CDCl3 gives three peaks because its I=1 so acc. to 2nI+1 2×1×1+1=3 so it gives 1:1:1 peaks Solvents used are CDCl3, DMSO, d6acetone, d6 benzene
  13. 13. 13C chemical shifts The most significant factors affecting the chemical shifts are: Electro negativity of the groups attached to the C Hybridization of C The intensity (size) of each peak is NOT directly related to the number of that type of carbon. Other factors contribute to the size of a peak: Peaks from carbon atoms that have attached hydrogen atoms are bigger than those that don’t have hydrogens attached. Carbon chemical shifts are usually reported as downfield from the carbon signal of tetramethylsilane (TMS).
  14. 14. Why Carbon-13 NMR required?  Carbon NMR can used to determine the number of non-equivalent carbons and to identify the types of carbon atoms(methyl, methylene, aromatic, carbonyl….) which may present in compound.  13C signals are spread over a much wider range than 1H signals making it easier to identify & count individual nuclei.
  15. 15. WHY 13C NMR REQUIRED ??  Proton NMR used for study of number of nonequivalent proton present in unknown compound.  Carbon NMR can used to determine the number of non- equivalent carbons and to identify the types of carbon atoms(methyl, methylene, aromatic, carbonyl….) which may present in compound.  13C signals are spread over a much wider range than 1H signals making it easier to identify & count individual nuclei.
  16. 16. CHARACTERISTIC FEATURES OF 13C NMR • The chemical shift of the CMR is wider(δ is 0-220 ppm relative to TMS) in comparison to PMR(δ is 0-12ppm relative to TMS). • 13C-13C coupling is negligible because of low natural abundance of 13C in the compound. • Thus in one type of CMR spectrum(proton de coupled) each magnetically non equivalent carbon gives a single sharp peak that does undergo further splitting.
  17. 17. CHARACTERISTIC FEATURES OF 13C NMR  The area under the peak in CMR spectrum is not necessary to be proportional to the number of carbon responsible for the signal. Therefore not necessary to consider the area under ratio.  Proton coupled spectra the signal for each carbon or a group of magnetically equivalent carbon is split by proton bonded directly to that carbon & the n+1 rule is follwed.  13C nucleus is about one-fourth the frequency required to observe proton resonance.  The chemical shift is greater for 13C atom than for proton due to direct attachment of the electronegative atom to 13C Gurdeep R. Chatwal, Sham K.Anand; Instrumental Methods Of Chemical Analysis, Enlarge edition 2002,Pg. no. 2.31-2.32
  18. 18. 13C CHEMICAL SHIFTS are measured in ppm (d) from the carbons of TMS • The correlation chart is here divided into sections 1) the saturated carbon atom which appear at Upfield,nearest to TMS(8- 60ppm). 2) effect of electronegative atom(40-80ppm) 3) Alkenes and aromatic carbon atom(100-170) 4) It contain carbonyl carbon bond. which appear at Downfield value(155- 200ppm). Pavia, Lampman, Kriz, Vyvyan; Spectroscopy, Cengage Learning, India edition, 2007, Pg. no. 177
  19. 19. 13C INTERPRETATION  Count how many lines- how many types of carbons  Symmetry duplicates give same line- if there are more carbons in your spectrum – symmetry  Check chemical shift window-  Check splitting pattern-  Signal height size-?
  20. 20. 13C INTERPRETATION 13C NMR spectroscopy provides information about:  The number of nonequivalent carbons atoms in a molecule  The electronic environment of each carbon  How many protons are bonded to each carbon
  21. 21. EXAMPLE PREDICTING CHEMICAL SHIFTS IN 13C NMR SPECTRA Solution  Ethyl acrylate has five distinct carbons: two different C=C, one C=O, one C(O)-C, and one alkyl C. From Correlation chart the likely absorptions are
  22. 22. CHEMICAL SHIFT Carbon-13 chemical shifts are most affected by,  Hybridiasation state of carbon & Electronegative group attached to carbon.
  23. 23. CORRELATION CHART
  24. 24. CHEMICAL SHIFT 020406080100120140160180200220 PPM 0246810 PPM 1H NMR 13C NMR 1H range = 0 to ~ 12 ppm 13C range = 0 to ~ 220 ppm
  25. 25. 1H AND 13C NMR COMPARED 13C signals are spread over a much wider range than 1H signals making it easier to identify and count individual nuclei Figure #1 shows the 1H NMR spectrum of 1-chloropentane; Figure #2 shows the 13C spectrum. It is much easier to identify the compound as 1-chloropentane by its 13C spectrum than by its 1H spectrum.
  26. 26. 1-CHLOROPENTANE 01.02.03.04.05.06.07.08.09.010.0 Chemical shift (d, ppm) ClCH2 CH3 ClCH2CH2CH2CH2CH3 1H
  27. 27. 1-CHLOROPENTANE Chemical shift (d, ppm) ClCH2CH2CH2CH2CH3 020406080100120140160180200 13C CDCl3 a separate, distinct peak appears for each of the 5 carbons
  28. 28. 13C CHEMICAL SHIFTS ARE MOST AFFECTED BY  hybridization state of carbon-  electronegativity of groups attached to carbon- Pavia, Lampman, Kriz, Vyvyan; Spectroscopy, Cengage Learning, India edition, 2007, Pg. no. 176-178 Easy use chart
  29. 29. PREDICTING 13C SPECTRA CH3 CH3 C C C C C CH3 plane of symmetry 4 lines O CH3 CH3 O CH3 CH3 C C c CH3 O CH3 5 lines CH3 C CH3 C CH3 H 5 lines
  30. 30. PREDICTING 13C SPECTRA CH3 CH3 H3C CH3 C C C CC C H3C CH3 4 lines C C CH3 CH3 CH3 CH3 C C CH3 CH3 CH3 CH3 2 lines Symmetry Simplifies Spectra!!!
  31. 31. C O CDCl3 (solvent) CH3CCH3 O CH3 C O CH3COCH2CH3 O OCH2 CH3 CDCl3 (solvent)
  32. 32. PROBLEMS OF 13 C • Natural abundance- 13 C natural abundance is very low (1.1%).  Gyro magnetic ratio- 13 C nucleus gyro magnetic ratio is much lesser than proton nucleus. 13 C-1.404; 1 H-5.585.  Coupling phenomenon- 13 C & 1 H have I=1/2 so that coupling between them probably occur. Y.R.Sharma,S.Chand; Elementary Organic Spectroscopy, India edition, 2009,Pg. no. 71
  33. 33. PROBLEMS IN NMR CAN BE OVERCOME BY  Fourier Transform Technique-  Decoupling Technique- 1) Broad Band Decoupling 2) Off Resonance Decoupling 3) DEPT (Pulse) Decoupling  Nuclear Overhauser Phenomenon-
  34. 34. SIGNAL AVERAGING AND FT-NMR  Low abundance of 13C is overcome by signal averaging and Fourier-transform NMR (FT-NMR)  Signal averaging  Numerous individual runs are added together and averaged such that random background noise cancels to zero and NMR signals are enhanced, substantially increasing sensitivity.
  35. 35. SIGNAL AVERAGING AND FT-NMR FT-NMR: (Pulse FT_NMR)  Sample is irradiated with entire range of useful frequencies  13C nuclei in the sample resonate at once giving complex, composite signal that is mathematically manipulated by Fourier transforms to segregate individual signals & convert them to frequencies. Advantages-  More sensitive-  Very fast- Pavia, Lampman, Kriz, Vyvyan; Spectroscopy, Cengage Learning, India edition, 2007, Pg. no. 121
  36. 36. Carbon-13 NMR spectra of pentan-1-ol. Spectrum (a) is a single run, showing background noise. Spectrum (b) is an average of 200 runs Signal Averaging and FT-NMR, Pentan-1-ol
  37. 37. 13 C-NMR SPIN-SPIN COUPLING  1 H NMR: Splitting reveals number of H neighbours. 13 C NMR: Limited to nuclei separated by just one sigma bond; no Pi bond. 1 H 13 C 13 C 12 C Coupling observed Coupling occurs but signal very weak, low probability For two adjacent 13 C 1.1% X 1.1% = 0.012% No Coupling No Coupling.
  38. 38. DECOUPLING TECHNIQUES • Irradiation of all 1H nuclei by using decoupler • 1H nuclei are saturated & C nuclei see zero coupling Proton or Noise Decoupling • Provides multiplet information keeping the spectrum simple. • Coupling between C & H attached directly to it off Resonance Decoupling • Involves complex program of pulse & delay times in C & H channel • C atoms attached to varying no. of H exhibit different phases DEPT
  39. 39. PROTON OR BROADBAND DECOUPLING a sample is irradiated with two different radiofrequencies. , These rapid transition decoupled any spin-spin interaction between 1H & 13C nuclei. Due to rapid change, all spin interactions are averaged to zero. Appear only 13C spectrum Disadvantage.-information on attached H is lost. Pavia, Lampman, Kriz, Vyvyan; Spectroscopy, Cengage Learning, India edition, 2007, Pg. no. 181 1-to excite all C nuclei 2-to cause all protons -rapid transition
  40. 40. Proton Decoupling Three types: 1. Broad band decoupling 2. Off-resonance decoupling 3. Pulse decoupling
  41. 41. Proton-coupled 13C splitting patterns
  42. 42. Broad band decoupling 1. It avoid spin-spin splitting of 13C lines by 1H nuclei. 2. In this, all the protons are simultaneously irradiated with a broad band radiofrequency signal. Irradiation causes the protons to become saturated and they undergo rapid upward downward transition among all their possible spin state. This is produced by a second coil located in the sample probe. 3. Without decoupling 13C spectra would show complex overlapping multiplets that would be hard to interpret. 4. The spin-spin information get lost, but we can use off-resonance decoupling to get spin-spin shifts back
  43. 43. 13C OFF-RESONANCE DECOUPLING  In this technique the 13C nuclei are split only by the protons directly bonded to them as a result the multiplets become narrow & not removed altogether as in fully decoupled spectra.  It simplifies the spectrum by allowing some of the splitting information to be retained.  The N + 1 rule applies: a carbon with N number of protons gives a signal with N + 1 peaks. P.S.Kalsi; Spectroscopy Of Organic Compounds, Sixth Edition:2004, Page no.-377
  44. 44. 13C OFF-RESONANCE DECOUPLED SPECTRUM 3 protons n+1=4 2 protons n+1=3 1 proton n+1=2 0 protons n+1=1 Methyl ‘C’ Methylene ‘C’ Methine ‘C’ Quaternary‘C’ P.S.Kalsi; Spectroscopy Of Organic Compounds, Sixth Edition:2004, Page no.-379 13C Off-resonance decoupled spectrum
  45. 45. OFF-RESONANCE DECOUPLING  Off-Resonance decoupling simplifies the spectrum by allowing some of the splitting information to be retained.  In this technique only the 13C nuclei are split by the protons directly bounded to them and not by any other protons i.e., one observes only one bond coupling 13C -1H  The coupling between each carbon atom and each hydrogen attached directly to it, n+1 rule. Use of off-resonance decoupled spectra has been replaced by use of DEPT 13C NMR
  46. 46. EXAMPLE: PROPANOL
  47. 47. 13C OFF-RESONANCE DECOUPLED SPECTRUM 1,2,2-trichloropropane P.S.Kalsi; Spectroscopy Of Organic Compounds, Sixth Edition:2004, Page no.-379
  48. 48. Nuclear Overhauser Enhancement (NOE) A. Under conditions of broad band decoupling it found that the area of the 13C peaks are enhanced by a factor that is significantly greater than that which is expected from the collapse of multiplets into single lines. B. This is a manifestation of nuclear overhauser enhancement. C. Arises from direct magnetic coupling between a decoupled proton and a neighboring 13C nucleus that results in an increase in the population of the lower energy state of the 13C nucleus than that predicted by the Boltzmann relation. D. 13C signal may be enhanced by as much as a factor of 3 x E. Disadvantage – 1. Lose the proportionality between peak areas and the number of nuclei of that type of 13C.
  49. 49. THEORY OF NOE Consider a hypothetical molecule in which 2 protons are in close proximity . In such compound, if we double irradiate Hb,then this proton gets stimulated and the stimulation is transferred through space to the relaxation mechanism of Ha. C C Ha Hb 59 Thus, due to increase in spin lattice relaxation of Ha, its signal will appear more intense by 15 to 50%. So, if the intensity of absorption of Ha signal is increased by double irradiating Hb, then protons Ha and Hb must be in close proximity in a molecule
  50. 50. Off-resonance decoupling 1. The coupling between each carbon atom and each hydrogen attached directly to it, s observed acc to n+1 rule. 2. Apparent magnitude of the coupling constant is reduced and overlap of the resulting multiplets is less frequent 3. Set decoupling frequency at 1000 to 2000 Hz above the proton spectral region which leads to a partial decoupled spectrum in which all but the largest spin spin shifts are absent.
  51. 51. HYDROGEN DECOUPLED MODE(BROAD BAND DECOUPLED)  A sample is irradiated with two different radio frequencies.  One to excite all 13C nuclei.  A second broad spectrum of frequencies to cause all hydrogen's in the molecule to undergo rapid transitions between their nuclear spin states.  On the time scale of a 13C-NMR spectrum, each hydrogen is in an average or effectively constant nuclear spin state, with the result that 1H-13C spin-spin interactions are not observed; they are decoupled.  Thus, each different kind of carbon gives a single, unsplit peak.
  52. 52. ETHYL PHENYLACETATE 13C coupled to the hydrogens 13C decoupled from the hydrogens -CH3 A 3+1=4 AB C B 2+1=3 -CH2 C, 2+1=3 -CH2
  53. 53. WHY DECOUPLE 13 C NMR
  54. 54. MESSY SPECTRUM SIMPLE
  55. 55. 25 MHz 13C NMR spectra of diphenyl selenide in CDCl3. Figure shows the fully coupled and decoupled 13C NMR spectra of diphenyl selenide. Although the large 1JC-H splittings are easy to identify, the fine structure of the individual multiplets is not first order (e.g., only the para carbon has an approximately centrosymmetric pattern, the others do not). This is because we are looking at the X part of an AA'BB'CX pattern (ABC are protons, X is carbon). Since the AA' and BB' parts are strongly coupled, we see the usual complex effects of "virtual coupling" on the X resonance . When noise {1H} decoupling is applied, the spectrum becomes much more intense, and only 4 lines remain, one for each carbon. In this compound we have a second magnetically active nucleus (77Se, natural abundance 7.5%, I = 1/2), so each of the 13C peaks has 77Se satellites, although coupling between C-4 and the selenium is too small to detect (the satellites are under the main peak).
  56. 56. Most 13C NMR spectra are very complex. The methyl carbon of an ethoxy group will appear as a large quartet, with each line further split into triplets. Even in fairly simple molecules each carbon may be coupled to a number of different protons. In complicated molecules, these multiplets overlap badly, and may be impossible to analyze. 1JCH = 100-250 Hz 2,3JCH = 2-10 Hz To simplify 13C spectra, we usually use some form of broadband decoupling (noise decoupling) to remove the effect of proton couplings. This also dramatically increases signal intensity, since now all carbons appear as singlets (assuming absence of other spin 1/2 nuclei like 31P or 19F). The increase is actually greater by a factor of 2-3 than would be predicted on the basis of simply combining the 13C multiplet intensities because the Nuclear Overhauser Effect causes additional increases in
  57. 57. DEPT 13C NMR Spectroscopy Distortionless Enhancement by Polarization Transfer (DEPT-NMR) experiment • Run in three stages 1. Ordinary broadband-decoupled spectrum • Locates chemical shifts of all carbons 2. DEPT-90 • Only signals due to CH carbons appear 3. DEPT-135 • CH3 and CH resonances appear positive • CH2 signals appear as negative signals (below the baseline) • Used to determine number of hydrogens attached to each carbon
  58. 58. Attached proton test spectra Another useful way of determining how many protons a carbon in a molecule is bonded to is to use an attached proton test (APT), which distinguishes between carbon atoms with even or odd number of attached hydrogens. A proper spin-echo sequence is able to distinguish between S, I2S and I1S, I3S spin systems: the first will appear as positive peaks in the spectrum, while the latter as negative peaks (pointing downwards), while retaining relative simplicity in the spectrum since it is still broadband proton decoupled. Even though this technique does not distinguish fully between CHn groups, it is so easy and reliable that it is frequently employed as a first attempt to assign peaks in the spectrum and elucidate the structure
  59. 59. Spectral Editing There are a number of multipulse experiments which render the signals in a 13C NMR spectrum with positive and negative intensities (sometimes zero) according to the number of attached protons. J-Modulated Spectra. This is the most primitive form of spectral editing. By placing a suitable delay time between the pulse and the beginning of the acquisition, spectra are obtained in which C and CH2 groups are positive, and CH and CH3 are negative. In this experiment, after the pulse there is a short delay, during which the decoupler is turned off, and the 13C NMR spectrum becomes modulated by the CH coupling frequency. After the delay the decoupler is turned on, and the FID is recorded. If the delay is 1/J then the quaternary and CH2 carbons are positive, and the CH and CH3 signals are negative. If the delay is 1/2J all peaks except quaternary are nulled
  60. 60. DEPT 13C NMR Spectroscopy DEPT 45 ALL H BEARING PEAKS
  61. 61. DEPT 13C NMR Spectroscopy (a) Ordinary broadband-decoupled spectrum showing signals for all eight of 6-methylhept-5-en-2-ol (b) DEPT-90 spectrum showing signals only for the two C-H carbons (c) DEPT-135 spectrum showing positive signals for the two CH carbons and the three CH3 carbons and negative signals for the two CH2 carbons SEE NEXT SLIDE
  62. 62. EXAMPLE: 6METHYLHEPT-5-EN-2- OL DEPT 135 DEPT 90 Ordinary broadband- decoupled spectrum
  63. 63. DEPT spectra of isopentyl acetate CH3, CH CH2 CH DEPT spectra of isopentyl acetate DEPT 45 ALL H BEARING PEAKS POSITIVE
  64. 64. COSY SPECTRUM  2D NMR spectra have two frequency axes and one intensity  The common 2D spectra are 1 H -1H shift correlations known as COSY Spectrum.  COSY identifies pair of protons which are coupled to each other.  The compound is identified using a contour plot  One dimensional counterpart of a given peak on the diagonal lies directly below that peak on each axis  The presence of cross peak normally indicates protons giving the connected resonance on the diagonal are geminaly or vicinally coupled. JUST FOR A VIEW
  65. 65. COSY SPECTRUM OF M- DINITROBENZENE
  66. 66. HECTOR SPECTRUM  2D-NMR spectra that displays 13C – 1H-NMR shift correlations are called HETCOR spectra. It shows coupling between protons and the carbon to which they are attached. The HETCOR spectrum of 1-chloro-2propanol is shown in the fig.  The 2-D spectrum is composed only of cross-peaks, each one relating carbon to its directly bonded proton(s).  The methyl doublet of 1H-NMR spectrum appears at δ 1.2 when drawn cross-peak and then dropped down to the 13C spectrum axis indicates that the 13C peak at δ 20 is produced by the methyl carbon of 1-chloro-2-propanol(C-3)  The 1H -NMR signal at δ 3.9 is due to CH-OH (C-2 proton) tracing out to the correlation peak and down to the 13C spectrum shows the 13C NMR signal at 67 arises from the C-2 carbon of the compound i.e., the carbon carrying the hydroxyl group.  The 1H-NMR peaks at δ 3.4-3.5 for the two protons on the carbon bearing the chlorine, the interpretation leads us to the cross-peak and down to the 13C peak at δ 51
  67. 67. THE HETCOR SPECTRUM OF 2-METHYL-3-PENTANONE HETCOR: Heteronuclear Chemical Shift Correlation indicates coupling between protons and the carbon to which they are attached
  68. 68. APPLICATIONS OF 13C NMR  CMR is a noninvasive and nondestructive method,i.e,especially used in repetitive In-vivo analysis of the sample without harming the tissues .  CMR, chemical shift range(0-240 ppm) is wider compared to H-NMR(0-14 ppm), which permits easy separation and identification of chemically closely related metabolites.  C-13 enrichment, which the signal intensities and helps in tracing the cellular metabolism.  CMR technique is used for quantification of drugs purity to determination of the composition of high molecular weight synthetic polymers.
  69. 69. Application’s • C-13 enrichment, which the signal intensities and helps in tracing the cellular metabolism. • C13 nuclei are a stable isotope and hence it is not subjected to dangers related to radiotracers. • .CMR technique is used for quantification of drug purity to determination of the composition of high molecular weight synthetic polymers.
  70. 70. EXAMPLES
  71. 71. Lead points before going to examples
  72. 72. -COOH -COCH3 -CH3
  73. 73. The off-resonance proton-decoupled 13C NMR spectrum for ethyl phenylacetate
  74. 74. 102 S N N S NH CH3 O NH2 CH3 3c Molecular Formula: C14H16N4OS2 C=O CH3 CH 13C NMR spectrum of 2-(Alanyl)-Amino-5-(4-methylphenyl)-5H-thiazolo[4,3-b]-1,3,4- thiadiazole (3c)
  75. 75. 103 S N N S N O Cl H3C 4d Molecular Formula = C20H16ClN3OS2 C=O CH3 CH-Cl CH 13C NMR spectrum of 3-chloro-1-[5-(4-methylphenyl)[1,3]thiazolo[4,3-b][1,3,4]thiadiazol-2-yl]-4- phenylazetidin-2-one (4d)
  76. 76. < > INEPT =Insensitive nuclei enhanced by polarization transfer
  77. 77. Example : 13C-NMR spectrum of diethyl phthalate
  78. 78. INTERPRETED SPECTRUM
  79. 79. JUST A VISUAL EXAMPLE JUST A VISUAL EXAMPLE
  80. 80. DEPT spectrum of isobutyl acetate
  81. 81. d (ppm) type of signal in DEPT represent 22 (b) positive 2 CH3 24 (c) positive CH3 24 (a) positive CH 37 (d) negative CH2 62 (e) negative CH2 170 (f) not present C of >C=O Interpretation :
  82. 82. DEPT spectrum of caryophyllene oxide
  83. 83. CH ONLY
  84. 84. C O =CH2
  85. 85. C O C-C-C
  86. 86. I-CH3 C-C-C
  87. 87. C O C O C-C-C CDCl3 (solvent)
  88. 88. C-C-C C-C-C CDCl3 (solvent)
  89. 89. C- Br
  90. 90. C-C-C CDCl3 (solvent)C-0
  91. 91. N-C-C OCH2 C-0
  92. 92. C O C-C-C CDCl3 (solvent) C=C C=C
  93. 93. The 13C NMR (APT, 50 MHz, DMSO-d6) study of the compound MIC-14 showed thirteen chemical shifts. Of these, seven were assigned to the quaternary carbons, two to the primary aliphatic carbons and four to the aromatic tertiary carbons. The carbons of the mesoionic ring of MIC-14 have chemical shifts in 152.1; 141.4 and 161.9 ppm assigned, respectively, to C2, C4 e C5 .The carbons C10 and C15 have chemical shifts of 40.6 and 21.4 ppm, while the aromatic carbons have chemical shifts of 132.7 (C6); 129.4 (C7, 7'); 123.8 (C8, 8'); 148.5(C9); 129.6 (C11); 129.8 (C12, 12'); 128.2 (C13, 13') and 139.1 (C14). http://dx.doi.org/10.1590/S0103-50532010000500024
  94. 94. For compound MIC-16 we observed a similar chemical behavior. The 13C NMR (APT, 50 MHz, DMSO-d6) spectrum showed thirteen signals. The carbons of the mesoionic ring showed chemical shifts of 148.7; 142.5 and 162.5 for C2, C4 and C5, respectively (see Carbons C10 and C15 show values of chemical shifts that are compatible with the N-methyl group in 40.8 and the methoxy group in 55.2. The aromatic carbons have chemical shifts of 132.6 (C6); 130.4 (C7, 7'); 124.6 (C8, 8'); 148.5 (C9); 121.3 (C11); 132.6 (C12, 12'); 114.3 (C13, 13') and 160.4 (C14).
  95. 95. 13 CNMR (DMSO, 75MHz) :δ 23.5, 82.1, 118.3, 122.2, 126.5, 126.9, 142.1, 167.4, 187.8 ppm. Teriflunomide,
  96. 96. LIONEL MY SON He was only in first standard in school when I was hit by a deadly one in a million spine stroke called acute transverse mylitis, it made me 90% paralysed and bound to a wheel chair, He cried bitterly and we had never seen him so depressed Now I keep Lionel as my source of inspiration and helping millions, thanks to millions of my readers who keep me going and help me to keep my son and family happy.
  97. 97. MY BLOGS ORGANIC SPECTROSCOPY INTERNATIONAL LINK….. http://orgspectroscopyint.blogspot.in/ ORGANIC SPECTROSCOPY INTERNATIONAL Organic Chemists from Industry and academics to Interact on Spectroscopy Techniques for Organic Compounds ie NMR, MASS, IR, UV Etc. Starters, Learners, advanced, all alike, contains content which is basic or advanced, by Dr Anthony Melvin Crasto, Worlddrugtracker, email me ........... amcrasto@gmail.com, call +91 9323115463
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