NMR TEST
The most powerful technique for determining the structure of organic compounds is nuclear
magnetic resonance spectroscopy (NMR). The physical phenomenon of nuclear magnetic
resonance (NMR) occurs when nuclei in a magnetic field absorb and re-emit electromagnetic
radiation. This energy has a specific resonance frequency that is determined by the strength
of the magnetic field.NMR spectroscopy determines the physical and chemical properties of atom
PROTON NMR(1H)
Proton nuclear magnetic resonance spectrum gives the information about that number of protons are present and their chemical environment in the compound
D2O Exchange
D2O Exchange 1H NMR spectrum is very helpful to identify the exchangeable protons(-COOH,-OH,-NH,-CONH-,-SH) as these protons are disappeared due to conveting to -COOD,-OD,-ND,-COND,-SD) after adding few drops of D2O to NMR sample solution
CARBON NMR(13C)
13C spectrum gives the information about that number of carbons are present and their chemical environment in the compound
FLUORINE NMR(19F)
19F spectrum gives the information about that number of Fluorines are present and their chemical environment in the compound
PHOSPHORUS NMR(31P)
31P spectrum gives the information about that number of phosphorus are present and their chemical environment in the compound
BORON NMR(11B)
11B spectrum gives the information about that number of Borons are present and their chemical environment in the compound
DEPT(45°,90°,135°)
DEPT(45°,90°,135°) is helpful to identify the number of CH,CH2 and CH3 carbons are present in the compound.
InDEPT 45° , All protonated carbons (CH,CH2,CH3)are detected as positive signals
InDEPT 90, only CH carbons detected as positive signals.
InDEPT 135, CH,CH3 carbons are detected as positive signals and CH2 signals are detected as negative signals
APT
Attached proton test(APT) is helpful to identify the number of CH,CH2,CH3 and quaternary carbons are present in the compound.
CH,CH3 carbon signals are detected as positive signals and CH2 and quaternary are detected as negative signals
PRESATURATION
During the relaxation delay at the frequency of the signal to be suppressed, a lengthy, low-power pulse is applied as part of the presaturation process. The signal’s intensity will be significantly reduced by such a pulse, which will saturate the undesirable resonance.
WET 1D
Wet D is a suppression technique that allows you to deliberately eliminate strong signals (up to 5) so that they are suppressed and your smaller peaks are more visible When using this method to saturate several signals, artifacts frequently appear, especially close to the saturated peaks.
NOESY1D
One-dimensional NOESY depends on detecting the NOE
effect at a different location while selectively inverting
or saturating one peak The experiments sensitivity is
decreased by the reliance on selective pulses which also restrict MDE to one 1H at a time.
ROESY1D
In ROESY spectra the sign of the cross-peaks is always opposite to that of the diagonal peaks and therefore ROESY is suitable for intermediate-sized molecules around kDa and smaller molecules in viscous solvents or at low temperatures.
TOCSY1D
We can use the TOCSY1D to reveal a fairly complete spin system for all resonances which are coupled to the selected peak
SPIN DECOUPLING
In order to get information about the scalar couplings in molecules by simplifying the NMR spectrum, spin decoupling or double resonance, which eliminates the spin spin splitting by a second radiofrequency field, was developed.
2D NMR
gcosy
homo nuclear (1H-1H) cosy experiment is helpful to identify the which proton is coupled with which proton
13C-HSQC
13C-HSQC experiment gives one bond correlation between 1H AND 13C. Here CH,CH3 comes as one coloured contours and CH2 comes as another colour. 13C-HSQC is used instead of HMQC for more crowded carbon spectra
13C -HMQC
13C-HMQC experiment gives one bond correlation between 1H AND 13C. Here CH,CH3 comes as one coloured contours and CH2 comes as another colour. Both HSQC AND HMQC gives same information .only pulse programe is different.
13C-HMBC
13C-HMBC Experiment is used to identify the two bond and 3 bond correlations between 1H and 13C. coupling constant range lies in between 2 to 14 Hz. Default jnxh value is 8 Hz. Based on jnxh value two bond and three bond corrlation contours detected in 13C-HMBC
CIGAR
CIGAR Experiment is used to identify the two bond and 3 bond correlations between 1H and 13C. Here both 2j,3j correlation contours are observed without changing jnxh value
15N-HSQC
15N-HSQC experiment gives one bond correlation between 1H AND 15N. Here NH,NH3 comes as one coloured contours and NH2 comes as another coloured contours
WET 1D
Wet 1D is a suppression technique that allows you to deliberately eliminate strong signals (up to 5) so that they are suppressed and your smaller peaks are more visible When using this method to saturate several signals, artifacts frequently appear, especially close to the saturated peaks.
NOESY1D
One-dimensional NOESY depends on detecting the NOE
effect at a different location while selectively inverting
or saturating one peak The experiments sensitivity is
decreased by the reliance on selective pulses which also restrict MDE to one 1H at a time.
ROESY2D
In ROESY spectra the sign of the cross-peaks is always opposite to that of the diagonal peaks and therefore ROESY is suitable for intermediate-sized molecules around kDa and smaller molecules in viscous solvents or at low temperatures.
TOCSY2D
2D TOCSY gives correlations between all protons within a given spin system
A TOCSY spectrum displays an entire chain of protons, each of which is coupled to the next
HOESY2D
In order to get information about the scalar couplings in molecules by simplifying the NMR spectrum, spin decoupling or double resonance, which eliminates the spin spin splitting by a second radiofrequency field, was developed.
SPECIAL NMR TESTS
Variable temperature NMR study( upto 100 degree centigrade) VT NMR
A kind of spectroscopy in which temperatures above or below the ambient probe temperature are used to identify how a nucleus with non-zero spin reacts to a perturbing magnetic field.High temperature NMR is very helpful to confirm rotamers and distinguising the diasteromers and rotatmers.
QUANTIFICATION NMR (QNMR):Assay of the compounds by using NMR technique
One of the rare methods of quantitative measurement without standards is qNMR, Without the need for standards with the same chemical composition, it can quantitatively assess diverse compound mixes.
DOSY
The NMR technique is known as diffusion-ordered spectroscopy (DOSY), which yields diffusion coefficients for specific resonances in NMR spectra. The main applications of DOSY are the oligomeric state of biomolecules and the analysis of small molecule mixtures
TFA CONTENT BY NMR
TFA content is confirmed by 19F NMR spectroscopy using external standard Tri fluoro methyl anisole
Residual solvent content by NMR
NMR spectroscopy can simultaneously identify and measure residual solvents typically with great sensitivity because solvents are low molecular-weight molecules.
Structure confirmation by NMR
The unambiguous sequence specific assignment of the 1H NMR spectrum of the peptide antibiotic using a variety of NMR tests has served as conclusive evidence of the chemical structure of the drug.
Structure elucidation of the compounds by using MASS AND NMR techniques
For the analytical examination of molecules and complicated mixtures, mass spectrometry is
a typical technique. It is crucial for figuring out a molecule. Elemental make-up and for
getting a partial picture of Its structure from mass spectral fragmentations. An unknown
organic compounds ultimate structure is always verified using a variety of independent
Techniques, including nuclear magnetic resonance spectroscopy (IR infrared spectroscopy
X Ray crystallography and other spectroscopic techniques