Simplification process of complex 1H NMR and13C NMR
- 1. SIMPLIFICATION PROCESS OF COMPLEX 1H NMR AND13C NMR SPECTRA PRESENTED BY DEVIKA GAYATRI.M 1st YEAR M.PHARM PHARMACEUTICAL CHEMISTRY
- 3. PRINCIPLE Absorption of energy occurs and a NMR signal is recorded. Applied Frequency = Precessional frequency, Radiofrequency is applied Spin of nuclei is aligned with the externally applied magnetic field. The nucleus spins on its axis and a magnetic moment is created in a precessional orbit, with a frequency called precessional frequency (Larmor frequency). Application of an external magnetic field (Ho) Proton or nucleus with odd mass number spins on its own axis.
- 5. TYPES OF PROTONS EQUIVALENT PROTON A set of protons with same environment are called equivalent protons NON –EQUIVALENT PROTON Sets of protons with different environments are called non equivalent protons
- 6. EQUIVALENT PROTONS NON EQUIVALENT PROTONS
- 8. NMR signal splits into doublet, triplet, quartet etc.
- 12. COUPLING CONSTANT • Separation between the lines of each doublet is equal.This constant is called the coupling constant J value. • It is measured in HZ • Identical for each signal • Independent of field strength
- 14. Complexity of spectra Overlapping of signals and spin coupling increases complexity of spectra Difficult to interpret Useful results are buried
- 16. ISOTOPE EXCHANGE • Deuterium-heavy isotope of hydrogen • Widely used because of easy introduction into the molecule its presence not detected in the spectrum • Smaller magnetic moment than hydrogen-absorbs at different field strengths • It broadens peak of neighbouring hydrogen-but does not splits-couples only slightly with hydrogen
- 17. Ethyl bromide • Deuterium replaces methyl hydrogens • Multiplicity of CH2 peaks changes from quartet to triplet to doublet to singlet
- 18. PROTONS ON α-CARBON ATOMS TO CARBONYL OR NITRO GROUPS
- 21. High field strength • Chemical shift difference between coupled protons become comparable to the coupling constant -Cause of complexity • Achievement of using larger magnetic field -spreading of ∆v relative to J • Spread out unresolved signals easily
- 23. • Coupling between neighbouring nuclei gives splitting patterns-in some cases complex patterns- spin decoupling • Irradiation of protons with intense radiofrequency energy-eliminates complete coupling
- 28. 2D NMR
- 29. • Correlation spectroscopy • Provide more information about molecule than 1D spectra • Used for molecules with complicated structure • 2D Spectrum • Increases spectral resolution by spreading overlapping peaks over two dimensions • Frequencies along both axis • Spectrum interpreted starting from diagonal-consist of series of peaks- called cross peaks
- 30. • CROSS PEAKS -Appear off the diagonal -Symmetrical along diagonal -Splitting between protons of adjacent carbon atoms -Indicate H atom spin spin coupled to each other • Peaks on diagonal that matches with cross peaks -coupled to each other
- 31. Coupling of methyl protons at1.1 ppm to the metylene protons at 2.8 ppm
- 32. NOE
- 39. Reduces sensitivity Complicates spectra Presence of large one bond J-coupling constants between carbon and hydrogen(typically from 100-250 HZ)
- 40. FT technique Decoupling technique Nuclear overhauser phenomenon for enrichment of the carbon signal.
- 41. Sensitivity of 13C can be increased by : FT-NMR instrumentation Distortionless Enhancement by Polarization Transfer(DEPT) Attached Proton Test Spectra (APT)
- 42. CONCLUSION • Simplification of spectra helps in i. clarification of spectra ii. identification of interacting protons iii. find out the hidden peaks • 2D Technique i. Increase spectral resolution by spreading overlapping peaks over 2 dimension ii. Simpification of interpretation of one dimensional spectra
- 43. • Difficulties encountered in identification of 13C NMR signals can be overcome by advanced instrumentation techniques.
- 44. REFERENCES • Practical pharmaceutical chemistry, A.H.Beckette, J.B.Stenlake, part two, fourth edition • Spectroscopy of Organic Compounds, P.S.Kalsi • Spectrometric Identification of Organic Compounds, Robert.M.Silverstein, Francis.X.Webster, Sixth edition • http://acdlabs.typepad.com/elucidation/Philosophy to chemistry to elucidation • www.chemwiki.ucdavis.edu