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13C-NMR
SPECTROSCOPY
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 radiofrequency field of certain
characteristic frequency.
 It results to give a spectrum with frequency on x-
axis and intensity of absorption on y-axis.
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
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
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.
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)
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
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
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.
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.
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
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).
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.
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.
CHARACTERISTIC FEATURES OF 13C NMR
• The chemical shift of the CMR is wider(δ is 0-220ppm relative
to TMS) in comparison to PMR(δ is 0-12ppm relative toTMS).
• 13C-13C coupling is negligible because of low natural
abundance of 13C in the compound. Thus in one type ofCMR
• spectrum(proton de coupled) each magnetically non equivalent
carbon gives a single sharp peak that does undergo further
splitting.
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
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
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-
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
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
CHEMICAL SHIFT
Carbon-13 chemical shifts are most affected by,
 Hybridiasation state of carbon & Electronegative group attached to carbon.
CORRELATION CHART
CHEMICAL SHIFT
020406080100120140160180200220
PPM
0246810
PPM
1H NMR
13C NMR
1H range = 0 to
~ 12 ppm
13C range = 0 to
~ 220 ppm
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.
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 appears for
each of the 5
carbons
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
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
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!!!
C
O CDCl3 (solvent)
CH3CCH3
O
CH3
C
O
CH3COCH2CH3
O
OCH2
CH3
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
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-
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.
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
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
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.
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
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
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 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
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
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
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, s observed acc to n+1 rule.
Use of off-resonance decoupled spectra has been replaced
by use of DEPT 13C NMR
EXAMPLE: PROPANOL
13C OFF-RESONANCE DECOUPLED SPECTRUM
1,2,2-trichloropropane
P.S.Kalsi; Spectroscopy Of Organic Compounds, Sixth Edition:2004, Page no.-379
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.
NUCLEAR OVERHAUSER ENHANCEMENT
 NOE effect for heteronuclear nuclei: when one of two different
types of atoms irradiated & NMR spectrum of other type is
determined they show change in absorption intensities of the
observed atom, enhancement occurred, is called nuclear
overhauser effect & the degree of increase in the signal is called
nuclear overhauser enhancement.
 Effect can be either positive or negative.
 in 13C interacting with 1H effect is positive.
 NOE is enhancement of signals,it add in to original signal
strength.Pavia, Lampman, Kriz, Vyvyan; Spectroscopy, Cengage Learning, India edition,
2007, Pg. no. 180
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
61
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
The carbon-13 spectrum from CH3I.
The NMR spectrum from the carbon-13 nucleus will
yield one absorption peak in the spectrum.
If the hydrogen spin system is saturated, the four lines collapse into a
single line having an intensity which is eight times greater than the outer
peak in the 1:3:3:1 quartet since 1+3+3+1=8 .
Adding the nuclear spin from one hydrogen
will split the carbon-13 peak into two peaks.
Adding one more hydrogen will split each of
the two carbon-13 peaks into two, giving a
1:2:1 ratio.
The final hydrogen will split each of the previous
peaks, giving a 1:3:3:1 ratio.
In reality, we see a single line with a relative intensity of 24.
The Nuclear Overhauser Effect (NOE)
62
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.
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.
ETHYL PHENYLACETATE
13C coupled
to the hydrogens
13C decoupled
from the hydrogens
in some cases
the peaks of the
multiplets will
overlap
this is an
easier
spectrum
to interpret
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
DEPT 13C NMR Spectroscopy
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
EXAMPLE: 6METHYLHEPT-5-EN-2-
OL
(a) Ordinary broadband-decoupled
spectrum showing signals for all
eight of 6-methylhept-5-en-2-ol
(a) DEPT-90 spectrum showing
signals only for the two C-H
carbons.
(b) DEPT-135 spectrum showing
positive signals for the two CH
carbons and the three CH3
carbons and negative signals for
the two CH2 carbons.
DEPT 13C NMR
SPECTROSCOPY
 Distortionless Enhancement by Polarization
Transfer (DEPT-NMR) experiment
 Run in three stages
DEPT spectra of isopentyl acetate
CH3, CH
CH2
CH
DEPT spectra of isopentyl acetate
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.
COSY SPECTRUM OF M-
DINITROBENZENE
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
HETCOR TECHNIQUE
Heteronuclear Chemical Shift Correlation :
 Carbon - Hydrogen
1H and 13C spectra plotted separately on two
frequency axes.
Coordinates of cross peak connect signal of carbon
to protons that are bonded to it.
 Other HETCOR technique-
 Carbon to Deuterium
 13C to 19F
 13C to 31P
Pavia, Lampman, Kriz, Vyvyan; Spectroscopy, Cengage Learning, India edition,
2007, Pg. no. 198
HECTOR SPECTRUM OF 1-CHLORO-2-PROPANOL
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
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.
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.
EXAMPLES
The off-resonance proton-decoupled 13C NMR spectrum for ethyl
phenylacetate
96
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)
97
S
N
N S
NH2
CH3
Molecular Formula: C11H11N3S2
CH3
13C NMR spectrum of 2-Amino-5-(4-methylphenyl)-5H-thiazolo[4,3-b]-1,3,4-
thiadiazole (1b)
98
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)
<
>
Example : 13C-NMR spectrum of diethyl phthalate
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
62 (e) negative CH2
170 (f) not present C of >C=O
Interpretation :
DEPT spectrum of caryophyllene oxide
2-HEPTANONE, CPD AND DEPT-35
O
CH3
DEPT-135
DEPT-90
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13 C NMR Spectroscopy by Dr Anthony Melvin Crasto

  • 1. 13C-NMR SPECTROSCOPY by DR ANTHONY MELVIN CRASTO Principal Scientist INDIA FEB 2016
  • 2. THIS IS A VAST TOPIC AND A SHORT OVERVIEW IS GIVEN AND IN NO WAY COMPLETE JUSTICE CAN BE DONE FOR THIS
  • 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. 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. 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. 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. 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. 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. 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.
  • 11. 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.
  • 12.
  • 13. 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.
  • 14. 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
  • 15. 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).
  • 16. 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.
  • 17. 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.
  • 18. CHARACTERISTIC FEATURES OF 13C NMR • The chemical shift of the CMR is wider(δ is 0-220ppm relative to TMS) in comparison to PMR(δ is 0-12ppm relative toTMS). • 13C-13C coupling is negligible because of low natural abundance of 13C in the compound. Thus in one type ofCMR • spectrum(proton de coupled) each magnetically non equivalent carbon gives a single sharp peak that does undergo further splitting.
  • 19. 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
  • 20. 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
  • 21.
  • 22. 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-
  • 23. 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
  • 24.
  • 25.
  • 26.
  • 27. 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
  • 28.
  • 29. CHEMICAL SHIFT Carbon-13 chemical shifts are most affected by,  Hybridiasation state of carbon & Electronegative group attached to carbon.
  • 31.
  • 32.
  • 33.
  • 34.
  • 35. CHEMICAL SHIFT 020406080100120140160180200220 PPM 0246810 PPM 1H NMR 13C NMR 1H range = 0 to ~ 12 ppm 13C range = 0 to ~ 220 ppm
  • 36. 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.
  • 38. 1-CHLOROPENTANE Chemical shift (d, ppm) ClCH2CH2CH2CH2CH3 020406080100120140160180200 13C CDCl3 a separate, distinct peak appears for each of the 5 carbons
  • 39. 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
  • 40. 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
  • 41. 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!!!
  • 43. 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
  • 44. 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-
  • 45. 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.
  • 46. 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
  • 47. 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
  • 48. 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.
  • 49. 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
  • 50. 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
  • 51. Proton Decoupling Three types: 1. Broad band decoupling 2. Off-resonance decoupling 3. Pulse decoupling
  • 53. 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
  • 54. 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
  • 55. 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
  • 56. 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, s observed acc to n+1 rule. Use of off-resonance decoupled spectra has been replaced by use of DEPT 13C NMR
  • 58. 13C OFF-RESONANCE DECOUPLED SPECTRUM 1,2,2-trichloropropane P.S.Kalsi; Spectroscopy Of Organic Compounds, Sixth Edition:2004, Page no.-379
  • 59. 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.
  • 60. NUCLEAR OVERHAUSER ENHANCEMENT  NOE effect for heteronuclear nuclei: when one of two different types of atoms irradiated & NMR spectrum of other type is determined they show change in absorption intensities of the observed atom, enhancement occurred, is called nuclear overhauser effect & the degree of increase in the signal is called nuclear overhauser enhancement.  Effect can be either positive or negative.  in 13C interacting with 1H effect is positive.  NOE is enhancement of signals,it add in to original signal strength.Pavia, Lampman, Kriz, Vyvyan; Spectroscopy, Cengage Learning, India edition, 2007, Pg. no. 180
  • 61. 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 61 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
  • 62. The carbon-13 spectrum from CH3I. The NMR spectrum from the carbon-13 nucleus will yield one absorption peak in the spectrum. If the hydrogen spin system is saturated, the four lines collapse into a single line having an intensity which is eight times greater than the outer peak in the 1:3:3:1 quartet since 1+3+3+1=8 . Adding the nuclear spin from one hydrogen will split the carbon-13 peak into two peaks. Adding one more hydrogen will split each of the two carbon-13 peaks into two, giving a 1:2:1 ratio. The final hydrogen will split each of the previous peaks, giving a 1:3:3:1 ratio. In reality, we see a single line with a relative intensity of 24. The Nuclear Overhauser Effect (NOE) 62
  • 63. 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.
  • 64. 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.
  • 65. ETHYL PHENYLACETATE 13C coupled to the hydrogens 13C decoupled from the hydrogens in some cases the peaks of the multiplets will overlap this is an easier spectrum to interpret
  • 66. 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
  • 67. DEPT 13C NMR Spectroscopy
  • 68. 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
  • 69. EXAMPLE: 6METHYLHEPT-5-EN-2- OL (a) Ordinary broadband-decoupled spectrum showing signals for all eight of 6-methylhept-5-en-2-ol (a) DEPT-90 spectrum showing signals only for the two C-H carbons. (b) DEPT-135 spectrum showing positive signals for the two CH carbons and the three CH3 carbons and negative signals for the two CH2 carbons.
  • 70. DEPT 13C NMR SPECTROSCOPY  Distortionless Enhancement by Polarization Transfer (DEPT-NMR) experiment  Run in three stages
  • 71. DEPT spectra of isopentyl acetate CH3, CH CH2 CH DEPT spectra of isopentyl acetate
  • 72. 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.
  • 73. COSY SPECTRUM OF M- DINITROBENZENE
  • 74. 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
  • 75. HETCOR TECHNIQUE Heteronuclear Chemical Shift Correlation :  Carbon - Hydrogen 1H and 13C spectra plotted separately on two frequency axes. Coordinates of cross peak connect signal of carbon to protons that are bonded to it.  Other HETCOR technique-  Carbon to Deuterium  13C to 19F  13C to 31P Pavia, Lampman, Kriz, Vyvyan; Spectroscopy, Cengage Learning, India edition, 2007, Pg. no. 198
  • 76. HECTOR SPECTRUM OF 1-CHLORO-2-PROPANOL
  • 77. 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
  • 78. 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.
  • 79. 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.
  • 81.
  • 82.
  • 83.
  • 84.
  • 85.
  • 86.
  • 87.
  • 88.
  • 89.
  • 90.
  • 91. The off-resonance proton-decoupled 13C NMR spectrum for ethyl phenylacetate
  • 92.
  • 93.
  • 94.
  • 95.
  • 96. 96 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)
  • 97. 97 S N N S NH2 CH3 Molecular Formula: C11H11N3S2 CH3 13C NMR spectrum of 2-Amino-5-(4-methylphenyl)-5H-thiazolo[4,3-b]-1,3,4- thiadiazole (1b)
  • 98. 98 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)
  • 99.
  • 100.
  • 101.
  • 102.
  • 103.
  • 104. < >
  • 105. Example : 13C-NMR spectrum of diethyl phthalate
  • 106.
  • 107.
  • 108.
  • 109. DEPT spectrum of isobutyl acetate
  • 110. 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 :
  • 111. DEPT spectrum of caryophyllene oxide
  • 112.
  • 115.
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Editor's Notes

  1. Y