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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.

2

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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ar er a ac e pro on e outdated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

4

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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

7

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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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