Spectroscopy

1.  Why NMR
 Why is it needed? What is it used for?
 To find out the required and side products in the reactions.
 To analysis and confirm the structures of the natural products.
 We use a variety of spectroscopic techniques-
 UV spectroscopy :-
 Gives the information about Chromospheres & conjugated systems
 IR spectroscopy : -
 Gives the information about the Functional groups
 Mass spectroscopy : -
 Gives the information about exact mass of the compounds.
A + B Product
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2.  1H NMR spectroscopy :
 Gives the information about no. of hydrogen's & the types of
hydrogen atoms.
 Gives the more detailed structural information & the most powerful
spectroscopic method used by organic chemists
 13C NMR spectroscopy :-
 Gives the information about no. of carbon & the types of carbon
atoms.
 It gives direct information about carbon skeleton in the
molecule.
 One Dimensional NMR
 The NMR spectra which have one frequency axis and one
intensity axis is known as One Dimensional NMR spectrum .
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3.  History of 13C NMR
 First CMR by Lanterbur and Holm, 1957
 PND (Proton Noise Decoupled) by Ernst, 1965
 F T CMR (Fourier Transform) by Ernst, Anderson,
1966
 ORD (Off Resonance Decoupled)
 APT (Attached Proton Test)
 DEPT (Distortionless Enhancement by
Polarization Transfer)
 INEPT (Insensitive Nuclei Enhanced
Polarization Transfer)
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4.  Physical Properties of 13C & 1H nucleus and its Spectrum
S. N. Nuclei 13C 1H
1 Relative abundance 1.11 99.98
2 Spin Q. N. (I) 1/2 1/2
3 Magnetic moment (μ) 0.7 2.8
4 Gyro magnetic ratio (γ) 1/4 1
5 Chemical shift (δ) Range 0-220 ppm 0-15 ppm
6 Relative sensitivity at natural
abundance
1.11/99.98
= 1/90
99.98/99.98
=1
Spectrum 13C 1H
7 Integration Signals can not
integrated
Signals can be
integrated
8 Spectrum Multi Scan
spectrum
Single Scan spectrum
9 Spectrum Simple spectrum Complex spectrum
10 Spectrum Well separated Less separated
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5.  Difference Between Physical Properties of 13C & 12C nucleus
S. N. 13C 12C
1 The relative natural abundance
is 1.11%
The relative natural abundance is
98.99 %.
2 It has magnetic moment
(I)=1/2
It has magnetic moment (I)= 0
3 It is magnetic in nature. It is non-magnetic in nature.
4 It is used for recording CMR. It is not used for recording CMR.
Number of CMR signals -
 The number of signals in CMR spectrum is equal to number of Sets/
kinds/types of carbon. (which depends on chemical environment)
 Similar to 1H NMR, Chemically equivalent carbon gives one sharp
signals
 While Chemically non-equivalent carbons gives different signals.
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6.  Indicate the Number of Signals expected in the CMR spectrum of the
following isomeric compounds (C8H18)
8
4
7
3
6
2
5
1
1
2
3
4
5
6
7 2
3
4
5
6
7
8
1
8
2
5
1
4
3
3
6
2
8
3
7
2
6
5
1
4
3
8
5
1
6
7
4
2
4
6
5
3
7
8
1
2
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7 8
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
6
7
8
1
2
3
4
5
(i) (ii) (iii) (iv)
(v) (vi) (vii) (viii)
(ix) (x) (xi) (xii)
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7. S N No. of sets
of Carbon
No. of CMR
signals
S N No. of sets
of Carbon
No. of CMR
signals
i 4 4 vii 7 7
ii 7 7 viii 3 3
iii 8 8 ix 4 4
iv 5 5 x 7 7
v 6 6 xi 6 6
vi 7 7 xii 2 2
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8.  Indicate the Number of Signals expected in the CMR spectrum of
the following Compounds
O O
O
CH3
Cl
Cl
a b
c
d
e f
g h i
j k
N
N
l
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9. S N No. of sets
of Carbon
No. of CMR
signals
S N No. of sets
of Carbon
No. of CMR
signals
a 1 1 g 8 8
b 1 1 h 4 4
c 5 5 i 3 3
d 7 7 j 4 4
e 3 3 k 5 5
f 4 4 l 1 1
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10.  Indicate the number of signals expected in the CMR spectrum of the
following isomeric compounds
X X
X
X
X
X
X
X
Y
X
Y
X
Y
X
X X
X
X
X
X
X
X
X
X
Y
X
X
Y
X
X
Y
X
Y
X
X
X
X
X
X
X
X
X
1 2 3 4 5 6 7
8 9 10 11 12 13
14 15 16
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11. S N No. of sets
of Carbon
No. of CMR
signals
S N No. of sets
of Carbon
No. of CMR
signals
1 4 4 9 4 4
2 3 3 10 6 6
3 4 4 11 4 4
4 2 2 12 6 6
5 4 4 13 6 6
6 6 6 14 6 6
7 6 6 15 2 2
8 2 2 16 4 4
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12.  Position of CMR signals :-Chemical shifts
 Chemical shifts values to different carbons
S. N. Hybridization Nature of Carbon Chemical shift
in δ or ppm
1 SP3 C-C 0-30 δ
C-X (O, N, S, Halogen)
C-C=,
30-60 δ
2 SP 60-100 δ
100-120 δ
3 SP2 C=C, C=N, C=S 100-150 δ
C=O 160-220 δ
Amide, Acid, Ester & Acid
Chloride, Acid anhydride
(C=O)
160-190 δ
Aldehyde & Ketone (C=O) 190-220 δ
Benzene C=C 128.5 δ
C C
C N
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13.  Comparison of 1H and 13C- Chemical Shifts
Group 1H 13C
 Cyclopropyl- 0.5-1.5 3-10
 CH3C 0.8-1.2 10-30
 CH3C=C 1.6-2.0 18-35
 H-C-C=O 2.5-2.7 35-52
 CH3 –O 3.3-4.2 53-75
 H-C ≡ C 2.5-3.0 65-95
 H-C ≡ N 3-3.2 115
 =CH2 4.5-5.0 100-120
 Aromatic 7-8 110-150
 R-CHO 9.7 182-205
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14.  Factors affecting the chemical shifts
1. Hybridization (Anisotropy)
2. Electronegativity
3. Resonance
4. Hyper conjugation
5. Steric effect
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15.  Chemical shifts of Alcohols & Ethers
OH
61.4
35
21.1
13.6
OH
23.6
32
9.9 68.7 OH
31.8
68.4
O
10.7
67.9
57.6
O
17.1
67.4
O
24
73.2
11.1
O O
O
O
O
24.9
27.7
69.5
66.5
92.8
64.9
28.6
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16.  Examples of alkene chemical shifts
136.2
115.9
113.3
140.2 124.6
126
117.5
137.2 137.2
107.1
149.7
127.2
130.8
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17.  Chemical shifts of carbon functional group
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H3C
O
OH
178.1
H3C
O
Cl
169.5
H3C
O
O
CH3
173.3
167.7
H3C
O
NH2
172.7
H3C
O
H H3C
O
CH3
199.8 206.4
H3C
O
O CH3
O

18.  Types of Coupling in 13CMR
1) 13C-13C coupling-
Not observed due low natural
abundance of 13C nuclei.
2) 13C-Ha coupling-
It is most commonly observed type of coupling.
It is also known as Residual Coupling
( J r =100-250 Hz)
3) 13C-Hb coupling- Long Range Coupling
Also commonly observed. ( J =1-20 Hz)
4) 13C-Hc coupling-Long Range Coupling
Also commonly observed. ( J =1-5 Hz)
C
OH
H
H
H
H
H
13
a
b
c
X
H
H
C
OH
H
H
H
H
H
13
a
b
c
H
H
C
OH
H
H
H
H
H
13
a
b
c
H
H
C
OH
H
H
H
H
H
13
a
b
c
H
H
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19. • In PND technique, all singlet are observed because all interactions between
protons and 13C nuclei are completely disappeared.
• This technique simplifies the spectrum & avoids overlapping multiplets.
• It has disadvantage that the information on attached hydrogen's is lost.
• In decoupling experiment, all the protons in the molecule are irradiating
simultaneously using second radiofrequency in the proper range.
• Due to double irradiation, each proton undergo rapid upward and downward
transition.
• Because of the rapid transition, spin interactions between protons and 13C
nuclei are completely disappeared
• Hence all singlets are appeared for all sets of carbon.
 Proton Noise Decoupled Spectra (PND)
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20.  Proton Noise Decoupled Spectra of 2-bromo butane
H3C
1
C
2
C
3
CH3
4
Br
H
H
H C1=12.6
C4=26.5
C2=35.3
C3=53.2
TMS
3/9/2022 20

21.  Off- Resonance Decoupled Spectra
 In many cases of the proton coupled spectrum, the information about
attached hydrogen is obtained, but the spectrum becomes highly
complex due to residual and long range couplings. Hence it is very
difficult to resolve and assign correctly.
 While in proton noise decoupling (PND) technique, all singlet are
observed. Hence unfortunately much useful information about the
attached hydrogen is lost.
 A second compromise method called off-resonance decoupling can often
provide multiplet information while keeping the spectrum relatively
simple.
 Similar to PND, in off-resonance technique also second radio-frequency
source is used for double irradiation. But in ORD, the decoupler is
set(held) to avoid complete decoupling.
 The off-resonance decoupled spectrum retains the coupling between
each carbon and directly attached proton but effectively removes long
range couplings.
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22.  Multiplicity/Spin-spin splitting:-
 In the off resonance decoupling technique
Multiplicity (N)= (2nI + 1)
where n = No. of protons directly bonded to carbon
I = Spin Q. N. of coupling Partner
For Hydrogen (I =1/2)
N = [(2n x 1/2) +1]
N = [n+1]
S
N
Nature of carbon No. of
coupling
partners (n)
Multiplicity
N = [n+1]
Known as
1 -C- (Quaternary Carbon ) 0 (0+1)=1 singlet
2 -CH- (Methine Carbon) 1 (1+1)=2 doublet
3 -CH2- (Methylene Carbon) 2 (2+1)=3 triplet
4 -CH3 (Methyl Carbon) 3 (3+1)=4 quartet
 Off- Resonance Decoupled Spectra
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23. HO
CH3
a
b
c
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24.  Examples on Multiplicity/ Splitting of CMR signals :-
 According to the off resonance decoupling technique
Multiplicity (N)= (2nI + 1)
where n = No. of protons directly bonded to carbon
I = Spin Q. N. of coupling Partner
For Hydrogen I =1/2
N = [(2n x 1/2) +1]
= [n+1]
S N Example Set a Set b Set c Set d
1 d d s --
2 s s quartet Triplet
3 s -- -- --
a
b
c
a
a
a
b
b
b
c
O
O
d
c
a
a
b
b
c
d
d
d
a
N
N
a
a
a a
a
3/9/2022 24

25. S N Example Set a Set b Set c Set d
4 q d s --
5 q t d --
6 q t d q
7 t t t --
3/9/2022 25
H3C
1
C
2
C
3
CH3
4
Br
H
H
H
1
2
O
3
2
O

26. Chemical Shifts of Common Solvents
Position of the signal in ppm
(No. of lines in carbon signal, multiplicity N= ( 2nI + 1)
where n = No. of coupling Partners
I= Spin Q. N. of Deuterium=1
1. CD3COOD (Deuterated Acetic acid) 20(7), 178.4(1)
2. CD3CN (Deuterated Acetonitrile ) 1.3(7), 111.7(1)
3. CD3COCD3 (Deuterated Acetone) 29.8(7), 206(1)
4. (CD3)2SO (Deuterated dimethyl methoxide) 39.5(7)
5. CD3OD (Deuterated Methanol) 49(7)
6. CD3NO2 (Deuterated Nitromethane) 57.7(7)
7. CCl4 (Carbon Tetrachloride) 96(1)
8. CDCl3 (Deuterated Chloroform) 77(3)
9. CD2Cl2 (Deuterated Dichloromethane) 53.8(5)
10. Dioxane-d8 67.4(5)
11. CS2 (Carbon disulfide) 192.8(1)
12. C6D6 (Deuterated Benzene) 128.5(3)
13. Pyridine-d5 149.9(3), 129.3(3), 135.3(3)
C C C
3/9/2022 26

27. 3/9/2022 27
 The attached proton test is a 1D 13C NMR experiment that is
used to assignment for separating quaternary carbons & CH2 signals
from CH & CH3 signals.
 The APT experiment gives positive signals for methine (CH)
and methyl (CH3) carbons and negative signals quaternary (C) and
methylene (CH2) carbons.
 It is slightly less sensitive than DEPT but a single experiment
shows all carbon signals at one time.
 In DEPT experiment signals of quaternary carbons suppresses
and requires up to three different acquisitions to get clear and full
information of all the carbons.
 APT (Attached Proton Test)

28. 3/9/2022 28
 APT spectrum of Ethylbenzene showing signals of CH &
CH3 positive while CH2 & quaternary C are negative
H2
C
CH3
a
b
c
d
d
e
e
f
a
b
c
Solvent Peaks
d, e, f

29.  DEPT (Distortionless Enhancement by Polarization Transfer)
• DEPT technique is used for determining the presence of primary, secondary
& tertiary carbon atoms signals from quaternary carbons & other carbons
with no attached protons in three steps.
• It is now much more widely used than proton coupling to determine the
number of hydrogens attached to a carbon.
• DEPT 13C spectrum does not show a signal for a quaternary carbons (carbon
that is not attached to a hydrogen).
• For Ex: 13CMR of 2-butanone shows 4 signals, as it has four sets of carbons,
whereas the DEPT shows only three signals because the quaternary carbonyl
carbon is not bonded to a hydrogen, so it will not produce a signal.
3/9/2022 29
H3C
1
2
3
CH3
4
O

30.  13C DEPT spectra enable different carbon
(CH3, CH2, CH, and quaternary)
 Types to be identified-
 DEPT 135: -CH2 peaks negative
-CH and CH3 peaks positive
 DEPT 90: only CH peaks visible.
 DEPT 45 : -CH2 and quaternary peaks negative
-CH3 and CH peaks positive
3/9/2022 30
 DEPT (Distortionless Enhancement by Polarization
Transfer)

31.  DEPT 13C NMR Spectra of Ipsenol
In CDCl3 at 75.6 MHz:
DEPT-90(A)-CH up.
DEPT-135(B),-CH3 & CH up, CH2 down.
At Bottom-PND13C NMR
3X CH-
3X CH, 2X CH3
4X CH2
3/9/2022 31
C2
C4
C7
C1
HO
1'
2
3
4
5
6
7
8
1
9

32.  Insensitive nuclei enhancement by polarization transfer (INEPT) is a
signal resolution enhancement method used in NMR spectroscopy.
 It is used to improve the sensitivity of NMR experiments on the nuclei
which have low abundance & low gyromagnetic ratio.
 The gyromagnetic ratio of 13C is 4 times lower than that of the proton, so
the signal intensity it produces will be 64 times lower than one produced
by a proton.
 The net effect in INEPT is the non-selective polarizarion transfer from
protons to 13C nuclei with the appropriate 1H-13C coupling.
3/9/2022 32
 INEPT (Insensitive Nuclei Enhancement by
Polarization Transfer)

33. 3/9/2022 33
 INEPT of 1,2-dibromo butane

34.  Assign the signals to the appropriate carbon
in the given compounds
8.0 (q), 22 (t), 42 (s), 64 (t, str.),
72 (t), 73 (t), 114 (t), 135 (d)
8 (q), 17 (q), 20 (q), 28 (t),
29(t), 34 (d), 35 (t), 49 (s),
72 (d) 82 (d) 85 (s), 123 (s),
125 (s), 135 (d), 143 (s)
3/9/2022 34
1
2
3
4
5
6 O 7
OH
8
OH
9
1
2 3
4
5
6
7
8
9
10
11
12
O
13
14 OH
15
OH
HO

35. Assignments
O
OH
OH
114
135
73
72
8
22
42
64
O
OH
OH
OH
8
135
143
125
85
85
72
49
35
34
29
28
20
17
3/9/2022 35

36.  Suggest structures for the following compounds based
on the given CMR data
1) C3H4O 50(t), 74(d), 84(s)
2) C3H7NO 14.3(q), 21.5(q), 155.2(s)
3) C3H4O2Br2 27(t), 40(d), 174(s)
4) C4H8O 14(q), 16(t), 46 (t), 202(d)
5) C4H6O 18.2(q), 134.9(d), 153.7(d), 193.4 (d)
6) C4H6O2 22(t), 28(t), 69 (t), 178(s)
7) C4H6O2 25(q), 100(t), 150 (d), 170(s)
8) C4H2O3 136.6 (d), 164.3(s, weak)
9) C4H5NO2 30.3(t), 183.6(s, weak)
10) C4H8O2 14.4(q), 20.2(q), 60.4(t), 170.7 (s)
11) C4H5O2Cl3 14 (q), 65 (t), 90(s), 161(s)
12) C4H7Br 17.5(q), 32.9(t), 127.8(d), 131(d)
3/9/2022 36

37. 3/9/2022 37
S. N. Structure S. N. Structure
01 07
02 08
03 09
04 10
05 11
06 12
C N H
H3C
CH3
14.3
21.5 155.2
C C CH2
H OH
74 84 50
27
40
174
Br OH
O
Br
16
46 202
H
O
14
153.7 134.9 193.4
H
O
18.2
O
O
28
178
22
69
150
25
170
O CH3
O
100
O
O
136.6
164.3
O
N
O
30.3
183.6
O
H
60.4
20.2
170.7
O
H3C
O
14.4
65
14
161
O
C
O
90
Cl
Cl
Cl
127,8 131 32.9
Br
17.5

38. 1) C5H8 17(t, mod.), 33(t, str.), 105(t, mod.), 150 (s, weak)
2) C5H8O 31(q, str.), 64(s, weak), 70(d, mod.), 90 (s, weak)
3) C5H14N2 32(t), 40(t), 45(q, str.), 58 (t)
4) C5H11Cl 22(q, str.), 25(d), 41 (t), 43(t)
5) C5H8O2 18(q), 53 (q), 125(t), 137(s), 168 (s)
6) C5H10O 21(q), 26(t), 34 (t), 67(t), 75 (d)
7) C5H8O2 14(q), 60(t), 129 (t), 130(d), 166 (s)
8) C5H11N 25.5 (t, weak), 27.6(t), 47.8 (t)
9) C6H10 13(q), 18 (t), 22 (t), 31 (t), 68 (d), 84 (s)
10) C6H12O 24(t, str.), 26(t, mod.), 36(t, str.), 70 (d, mod.)
11) C6H10O 20 (q), 31 (t), 32(d), 38 (t), 46 (t), 219(s)
12) C6H8O 19(q), 130.2(d), 130.4(d), 141.6(d), 152.3 (d), 193(d)
13) C6H15ON 27(t), 28(t), 34(t), 35 (t), 43 (t), 63 (t)
14) C6H6N2O 123(d, str.), 130(s, weak), 136(d, str.), 147 (d, str.),
152 (d, str.), 167 (s, mod.)
3/9/2022 38

39. 3/9/2022 39
01 08
02 09
03 10
04 11
05 12
06 13
07 14
CH2 105
150
33
33
17
H C C C
OH
CH3
CH3
31
64
90
70
32
40
45
H3C
H
N
H
N
CH3
41
25
43
Cl CH3
CH3
22
H2C
OCH3
O
H3C
125
137
18
168
53
26
34
21 67
75
H3C
H2
C
C
H2
HC
CH2
O
130
166
129 60
14
H2C
O
O
25.5
27.6 47.8
NH
47.8
27.6
22
13
H C C
H2
C
H2
C
18
31
84
68
H2
C CH3
26
24
36
24
OH
36
70
219
46
31
38
20
O CH3
32
63
28
34
35
27
43
H2N
OH
136
N
NH2
O
147
123
167
130
152
152.3
H3C C
H
C
H
C
H
C
H
193
141.6 130.4
130.2
C H
19

40. 1) C7H16O2 7(q*), 22(t*), 41(s, weak), 67.6 (t*) *equally strong
2) C8H18 14.2(q), 23.2(t), 29.6 (t), 32.5(t)
3) C8H18 25(d), 25.5(q, str.), 30.2(q, very str.), 31.2 (s), 33.4 (t)
4) C10H20 14(q), 23(t), 29(t), 29.4(t), 29.6 (t), 29.8 (t), 32.2 (t),
34.1 (t), 114.7 (t), 139.2 (d)
5) C8H12O2 15.2(q, mod.), 15.4(q, mod.), 20 (q, str.), 54 (s, mod.
weak), 104 (s, mod. weak), 142 (s, mod. weak),
173(s, weak)
6) C8H8O3 52 (q, str.), 112.9 (s), 117.9 (d, str.), 119 (d, str.), 130
(d, str.), 135 (d, str.), 162.4 s, str.), 170(s)
7) C8H8O 50.8(t), 52.1 (d), 125.4 (d, str.), 128 (d), 128.4 (d, str.),
137(s, weak)
8) C8H11N 13(q, 941), 23.9(t, 649), 115.4(d, 638), 118.6 (d,
935), 126.3 (d, 944), 128 (s, 155), 128.4 (d, 1000),
144.3 (s, 305)
3/9/2022 40

41. 3/9/2022 41
01 02
03 04
05 06
07 08
22 67.6
41
7
OH
H3C
OH
CH3
29.6
14.2 32.5
23.2
a
a
b
b
c
c
d
d
30.2
a
b
c
d
C
CH
H3C CH3
CH3
CH3
H3C
a
a
e
31.2
CH2
e
33.4
25
25.5
34.1
114.7 32.2
139.2
a
h
g
b
c
f
e
d
i j
29.6
29
14
29.8
29.4
23
142
104
15.4
54
20
173
15.2
O
O
CH3
CH3
OCH3
O
OH
135
130
119
117.9
112.9
162.4
170
52
128
128.4
125.4
137
O
50.8
52.1
NH2
CH3
118.6
128
115.4
126
128.4
144.3
23.9
13

42. 1) C9H11NO 39.7 (q, str.), 110.8 (d, str.), 124.9 (s, weak), 131.6
(d, str.), 154.1 (s, weak), 189.7 (d, mod.)
2) C9H12 21.2 (q), 127.2(d), 137.5(s)
3) C9H10O 8.2 (q, 360), 31.6 (t, 361), 128 (d, 820), 128.6
(d, 1000), 132.8 (d, 430), 137.2 (s,128),
196(s, 132)
4) C9H10O3 56(q), 56.1(q), 109.4(d), 110.7(d), 126.5 (d),
130.3 (s*), 149.8 (s*), 154.6 (s*), 190.7 (d) *weak
5) C9H8O3 115.4(d, 463), 115.6(d, 1000), 125.4(s, 202),
130(d, 944), 144.2 (d, 347), 159.7 (s, 297),
168.1 (s, 267)
6) C12H14O4 14.2(q*), 61.5(t*), 129(d*), 131.1(d*), 132.7
(s#), 167.5(s#) *equal intensity, # weak
7) C14H10O2 128.9(d, str.), 129.7(d, str.), 133(s, weak),
134.7 (d, mod.), 194.7(s, weak)
3/9/2022 42

43. 3/9/2022 43
01 02
03 04
05 06
07
O
H
154.1
110.8
131.6
124.9
189.7
N
39.7
CH3
CH3
H3C
21.2
137.5
127.2
O
128.6
128
132.8
137.2
196
31.6
8.2
O
H
149.8
109.4
110.7
130.3
189.7
H3CO
56
OCH3
56.1
154.6
126.5
O
115.4
115.6
130
159.7
125.4
168.1
144.2
OH
O
O
115.4
115.6
130
159.7
125.4
168.1
144.2
OH
O
128.9
129.7
134.7 133
194.7
O
O