L7 2D NMR
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Transcript of L7 2D NMR
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Off-Resonance 1H Decoupling
Now
C nuc ei are sp it on y y t e protons attac e directlyto them. 1H-13C coupling is restricted to one-bond only.
resonance (away) from the middle of the proton chemicalshift range and using a short band width irradiation
1
The N+ 1 rule applies: a carbon with Nnumber of protons
gives a signal with N+ 1 peaks.
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Inter retin13
C NMR The number of different signals indicates
the number of different kinds of carbon. The location (chemical shift) indicates the
type o unctiona group.
The peak area indicates the numbers ofcar ons n egra e .
The splitting pattern of off-resonance
protons attached to the carbon.
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13
3Useful information is retained keeping the spectrum simple
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DEPT(Distortionless Enhanced Polarization Transfer)
ar er a ac e pro on e outdated
- o ern ec n que a prov es same
information as off-resonance technique ar a e pu se ang e ,
All the peaks remain decoupled singlets
Transfer of polarization from attachedprotons to carbon - the no. of protonsdetermines how this transfer occurs
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Stages of DEPT1. The normal decoupled scan, in which each typeof 13C nucleus appears as a singlet.
2. The DEPT-90 scan, in which only the CH(methine) carbons bonded to exactly one proton
appear.
3. The DEPT-135 scan, in which the CH3 (methyl)
groups an me ne groups appear norma y,and the CH2 groups give negative peaks. Carbons
.
5
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This information allows us to distinguish among
carbons bonded to 0, 1, 2, or 3 h dro en atoms: Carbons with no H's appear only in the normalspectrum, but not in either DEPT spectrum.
Methine carbons (CH) give normal positivepeaks in all three spectra. Methylene (CH2) carbons give normal peaks in
the normal spectrum, no peaks in the DEPT-90spec rum, an nega ve pea s n e -spectrum.
e y 3 car o g ve or a ea enormal spectrum, no peaks in the DEPT-90 -,
spectrum. 6
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Summary of DEPT
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13CNMRspectrumandDEPTspectraofbut3en2one.
Chapter13 8
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135
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of frequency Vs intensity i.e. a 2D,
refers to frequency (time).
3D plot, the 2D in this case are both
omitted.
e w no scuss pu se sequences
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1&2DNMR
Gated Decoupling
Evolution period is varied
It requires 2 FT at right angles to each other on 2 independent time axes
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ets oo atthe application
In all 2D expts. we detect a signal
(During acquisition) as a fn of t2However this signal has beenmodulated as a fn of t1.
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NMR of monoter enes
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Ipsenol Integrate the spectrum18 H, 4CH2groups
H-10C10H18O
H-8
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Ipsenol
Diastereoto ic Cs
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1H-1H COrrelation S ectrosco Y(COSY)
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Double uantum Filtered1H-1H COSY
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Carbon detected HETeronuclear CORrelation13
C-1
H COSY HETCORCH2 CH2
C
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Proton detectedHeteronuclear Multiple Quantum Correlation
13 1
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NMR of Carboh drates
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Identification
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Identification
. -form J ~ 3-4 Hz -form J ~ 8 Hz
. annose an coup ng cons an are sma .
Same is the case with L-rhamnose
3. Magnet c an sotropy ue to r ng current e ects r ng or entat on n e
In 1H NMR in general -glycoside C-1 proton appears upfield
-form anomeric H appears between 5-5.8 ppm and-form appears below 5 ppm (between 4-5 ppm)
In 13C NMR it is reversed
-form anomeric C appears between 85-95 ppm and-form anomeric C appears between 100-105 ppm
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1H 13C l ti HMQC
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1H-13C correlation HMQC
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Identification
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Identification
. -form J ~ 3-4 Hz -form J ~ 8 Hz
. annose an coup ng cons an are sma
So we use NOESY,1
JCH coupling constant (~160 Hz for and 170 for )and H5 comes as a broad singlet in the region 3.1-3.3 ppm for -isomer
a t or enzy ene protecte counterpart; n - somer t s 3.6-3.9 ppm
Hudsons isorotation rule -mannoside has less + ve/ more ve Sp. Rot.
3. Magnetic anisotropy due to ring current effects ring orientation in field
In 1H NMR in general
-form anomeric H appears between 5-5.8 ppm and
-form appears below 5 ppm (between 4-5 ppm)In 13C NMR it is reversed
-form anomeric C appears between 85-95 ppm and
-form anomeric C appears between 100-105 ppm
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Alginate disaccharide skeleton: case study
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Alginate disaccharide skeleton: case study
3A MS, DMTST
o
OO
OPh
BnO STol
OAc
OHOBnO
BnO
+, , ,
O
OO
O
BnO
OOBnO
TfO
OO
O
BnO
BnOO
OO
Ph
BnOAcO
OO
O
BnO
BnOO
OO
Ph
BnOAcO
OO
O
BnO
BnOO
OO
Ph
BnOAcO
NaOMe/MeOH
Pyridine/Tf2O
, a 2,
15-crown-5, 18h
62%
OOBnO
BnOOOOPhBnO
Chi,Kulkarni,ZuelettaandHung Chem.AsianJ.2008,4,386390.
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H3
H1
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