C8953
NMR structural analysis - seminar
Vector model & edited 13C NMR spectra
Jan Novotný
176003@mail.muni.cz
March 13, 2024
Determine percentage of dominant regioisomer in
attached 1
H spectrum:
Determine percentage of dominant regioisomer in
attached 1
H spectrum:
72%
Diastereotopicity1
Determine the equivalency of
geminal protons
1
http://www.chem.wisc.edu/areas/reich/chem605/
Diastereotopicity1
Determine the equivalency of
geminal protons
1
http://www.chem.wisc.edu/areas/reich/chem605/
Values of chemical shift of important solvents
Abbr. Formula 1
H 13
C
ACN CH3CN 1.9 118
Benzene C6H6 7.2 128
CHCl3 7.2 77
DCM CH2Cl2 5.3 54
DMF (CH3)2NCHO 2.9, 8.0 32, 163
DMSO (CH3)2SO 2.5 40
MeOH CH3OH 3.3, 4.8 49
Water H2O 4.8 EXPLAIN
effect of solvent on the position of residual 1H water
signal:
CHCl3 - 1.6, ACN - 2.1, DMSO - 3.3, MeOH - 4.9
Analysis of simple pulse sequences using vector
model
▶ simple model based on rotation of the vector of bulk magnetization in the plane
perpendicular to the vector of magnetic field, direction is determined by the
"right-hand rule"
▶ NMR signal is detectable only as coherent magnetization oscillating in xy plane
▶ the free precession ω (due to the B0) of magnetization vector is eliminated by
introducing rotating frame ω0 ⇒ magnetic field of excitation pulses (B1) is
motionless and the individual resonance frequencies differs in so called offset
Ωi = ωi − ω0
▶ applicability of vector model is rather limited to simple single-quantum
experiments without transfer of polarisation
x
y
z
B0
Bpulse
T1 relaxation
Apply following sequence (inversion recovery) to isolated spin characterized by
a) τ = 2 ∗ T1 and b) τ = 0.2 ∗ T1. Draw semi-quantitatively resulting spectrum.
τ
180x 90y-
T1 relaxation
Apply following sequence (inversion recovery) to isolated spin characterized by
a) τ = 2 ∗ T1 and b) τ = 0.2 ∗ T1. Draw semi-quantitatively resulting spectrum.
τ
180x 90y-
x
y
z
x
y
z
x
y
z
x
y
z
x
y
z
x
y
z
+0.73M0
-0.65M0
Processing simulated NMR signal:
Processing simulated NMR signal:
1-1 sequence
Draw the evolution of macroscopic magnetization through the sequence:
90(y) - τ - 90(y) - aq
Consider the evolution of an isolated spin due to the chemical shift.
1. How does the result differ for the following offsets: Ωτ = 0, π/2, π.
2. Draw lineshapes of resulting signal assuming the a) y+ b) x+ corresponds to zero
phase of receiver (prior phase correction).
τ
90y 90y
1-1 sequence
Draw the evolution of macroscopic magnetization through the sequence:
90(y) - τ - 90(y) - aq
Consider the evolution of an isolated spin due to the chemical shift.
1. How does the result differ for the following offsets: Ωτ = 0, π/2, π.
2. Draw lineshapes of resulting signal assuming the a) y+ b) x+ corresponds to zero
phase of receiver (prior phase correction).
τ
90y 90y
x
y
z
x
y
z
x
y
z
0
π/2
π
x
y
z
0
π/2
π
ω ω
y+ x+
Heteronuclear spin echo
By using vector diagrams determine the result of attached pulse sequence.
1. Ignore 180 pulse in hydrogen channel for isolated spin systems a) 13C-1H and
b) 13C-1H2. Explain the role of CPD block.
2. Lets consider the complete sequence and isolated spin systems a) 13C-1H and
b) 13C-1H2.
τ=1/2J
90y 180x
13
C
τ=1/2J
180x
1
H
CPD
Heteronuclear spin echo
By using vector diagrams determine the result of attached pulse sequence.
1. Ignore 180 pulse in hydrogen channel for isolated spin systems a) 13C-1H and
b) 13C-1H2. Explain the role of CPD block.
τ=1/2J
90y 180x
13
C
τ=1/2J
1
H
CPD
x
y
z
x
y
z
x
y
z
CH...J=JHC
CH2...J=2*JHC
CHα
CHβ
y
+Ωτ
x
y
z
y
+Mx
+Mx
+πJτ
-πJτ
CHαCHβ
CHβ
CHα
+Ωτ
CH2αα CH2αα
CH2αα
CH2ββ CH2ββ
CH2ββ
Heteronuclear spin echo
By using vector diagrams determine the result of attached pulse sequence.
2. Lets consider the complete sequence and isolated spin systems a) 13C-1H and
b) 13C-1H2.
τ=1/2J
90y 180x
13
C
τ=1/2J
1
H
CPD
x
y
z
CH...J=JHC
CH2...J=2*JHC
y
x
y
z
y
180x
y
y
-Mx
+Mx
CH2ββCH2αα
CH2αα
CH2αα
CH2αα CH2ββ
CH2ββ
CH2ββ
CHβ CHβ
CHβ
CHβ
CHα
CHα
CHα
CHα
APT - Attached Proton Test
based on heteronuclear spin-echo
▶ t1 = 1/1JCH
phase of 13
C signals resolved according to number of
attached 1
H
▶ Cq, CH2 positive
▶ CH, CH3 negative
Different 1
JCH =⇒ different intensities
90x 180y
180
H-1
C-13 acq
dec
t1
-1
-0.5
0
0.5
1
0 0.5 1 1.5 2
Relativeintensity
t1 (1/1
JCH)
Cq
CH
CH2
CH3
13
C APT Cinnamic acid
13
C APT Cinnamic acid
9 DMF
7
1
2,6 3,5
4 8
13
C APT Nicotine
13
C APT Nicotine
11
10
9
127
3
2,6
54
DEPT experiment
DEPT experiment
+CH
-CH2, +CH, +CH3
+all
93
1,2
4
10
8
7
3,6,53
94
Next topic
2D NMR - homonuclear experiments