BY:Wasim Khalili

1D NMR Pulse Sequence

Spectrum (EtOH)

PreparationPreparation spin system relaxes and then excited by r.f.

Evolution Evolution (t1) chemical shifts & spin-spin couplings evolve. This is the timedomain which is incremented during a 2D experiment

MixingMixing r.f. pulses are applied and create observable transverse magnetization

Detection Detection (t2) observable transverse magnetization is recorded. It is usually labeled with t2

Four periods in 2D experiment

1. Primary 2D matrix consists of a series of FIDs.

2. A set of 1D NMR spectra is obtained by Fourier transformation with respect to t2

3. The signals of each transformation may differ in amplitude and phase. A second Fourier transformation with respect to t1 yields the final 2D matrix with frequency axes F1 and F2

1. 2. 3.

2D NMR

2D NMR

Spectrum

Pulse Sequence

This is how 2d NMR graph looks like

                                                                              

                                                                                                                                    

2D NMR

Phases...Now you can notice the spots on this line which is called diagonal (same information from 1d NMR) But there is extra spots here which refers to the correlation between neighboring atoms

Here you can notice how 2d NMR magnifies the signal and it well appear in a 3d shape like here

Now here after 2 FT we well got this shapeThe dotted line refers to negative signal and the rigged line refers to the positive onesAlso the no. of circles refers to the height of the signal and by that we can determine small signals from big ones

2D NMR

2D NMRThis graph describes how by changing t1 you can get this 3d signal in 2d NMR

2D J-resolved

COSY L.R. TOCSY

COSY 45. COSY 90. COSY DQF. TOCSY.

Relayed COSY. (with one homonuclear

relayed).

NOESY. ROESY.

Her

e ar

e th

e ty

pes

of 2

d N

MR

Y

ou c

an s

ee th

at e

very

type

rec

ord

a di

ffer

ent c

orre

latio

n si

gnal

I am

goi

ng to

des

crib

e th

e im

port

ant o

nes

But

I w

ant y

ou to

kno

w th

at j

refe

rs to

the

corr

elat

ion

sign

al

betw

een

tow

ato

ms

and

n is

how

far

thes

e to

w a

tom

s ar

e fa

r fr

om e

ach

othe

r

H,H- COSY Experiment

N≤3JHH

First type Correlation spectroscopy ( COSY)

•The first and most popular two-dimension NMR experiment is the homonuclear correlation spectroscopy (COSY) sequence, which is used to identify spins which are coupled to each other.

•COSY spectra show two types of peaks. Diagonal peaks have the same frequency coordinate on each axis and appear along the diagonal of the plot, while cross peaks have different values for each frequency coordinate and appear off the diagonal.

•Diagonal peaks correspond to the peaks in a 1D-NMR experiment, while the cross peaks indicate couplings between pairs of nuclei

•Cross peaks result from a phenomenon called magnetization transfer, and their presence indicates that two nuclei are coupled which have the two different chemical shifts that make up the cross peak's coordinates.

•Each coupling gives two symmetrical cross peaks above and below the diagonal. That is, a cross-peak occurs when there is a correlation between the signals of the spectrum along each of the two axes at these values.

•One can thus determine which atoms are connected to one another (within a small number of chemical bonds) by looking for cross-peaks between various signals.

TOCSY of strychnine

N>3JHH

The second type am going to discuss is the Total correlation spectroscopy or TOCSYThe TOCSY experiment is similar to the COSY experiment, in that cross peaks of coupled protons are observed. However, cross peaks are observed not only for nuclei which are directly coupled, but also between nuclei which are connected by a chain of couplings. This makes it useful for identifying the larger interconnected networks of spin couplings.

COSY & TOCSYIn

this

sli

de y

ou c

an s

ee th

e di

ffer

ence

eas

ily

NOESY of strychnine

xJHH

Third type is the Nuclear Overhauser effect spectroscopy (NOESY)This method establishes correlations between nuclei which are physically close to each other regardless of whether there is a bond between them. They use the Nuclear Overhauser effect (NOE) by which nearby atoms (within about 5 Å) undergo cross relaxation by a mechanism related to spin–lattice relaxation.

C,H Correlation by Polarization Transfer (HETCORHETCOR)

1JHC

Forth type is Heteronuclear through-bond correlation methods or HETCORHeteronuclear correlation spectroscopy gives signals based upon coupling between nuclei between two different types. Often the two nuclei are protons and another nucleus (called a "heteronucleus").You can see here at f1 is H and in f2 is C .. not identical

Basic HSQC Experiment

1JHC + JHH

5 .. Heteronuclear single-quantum correlation spectroscopy (HSQC)HSQC detects correlations between nuclei of two different types which are separated by one bond. This method gives one peak per pair of coupled nuclei, whose two coordinates are the chemical shifts of the two coupled atoms.

Basic HMQC Experiment

F2 displays the doublets with the spin coupling constant 1J(C-H) in addition to the H,H spin coupling.

1JHC + JHH

6- is Heteronuclear multiple-quantum correlation spectroscopy (HMQC) which gives an identical spectrum as HSQC, but using a different method. The two methods give similar quality results for small to medium sized molecules, but HSQC is considered to be superior for larger molecules

Basic HMBC Experiment

Cross signals caused by 1J of C-6 and C-3 are still observable but those arising from 3J and 2J are predominant.

2→4JHC

7- is Heteronuclear multiple-bond correlation spectroscopy (HMBC)HMBC detects heteronuclear correlations over longer ranges of about 2–4 bonds.