Carbon 13 NMR
20 likes4,120 views
Carbon-13 NMR spectroscopy provides detailed structural information about molecules. It works by applying a magnetic field to carbon-13 isotopes, which have spin, and measuring the energy required to excite these nuclei. The number of signals indicates the number of different carbon atom environments, while chemical shifts reveal functional groups. Coupling patterns show neighboring protons. This technique is useful when hydrogen NMR cannot be used, and for tracing metabolism and determining drug purity.
Carbon 13 NMR
- 1. JIWAJI UNIVERSITY CARBON-13 NMR PRESENTED BY AJAY MISHRA
- 2. NMR NMR is a research technique that exploits the magnetic properties of certain atomic nuclei. It determines the physical and chemical properties of atoms or the molecules . It can provide detailed information about the structure, dynamics, purity determination.
- 3. PRINCIPLE OF NMR • The principle behind NMR is that many nuclei have spin and all nuclei are electrically charged. If an external magnetic field is applied, an energy transfer is possible between the lower energy to a higher energy level . The energy transfer takes place at a wavelength that corresponds to radio frequencies and when the spin returns to its lower level, energy is emitted at the same frequency. The signal that matches this transfer is measured in many ways and processed in order to yield an NMR spectrum for the nucleus concerned.
- 4. KEY POINTS OF NMR • Because of its charge and spin, a nucleus can behave like a magnet. • NMR spectroscopy operates by applying magnetic filed to nuclei and then measuring amount of energy necessary to put various nuclei in resonance. • Nuclei in different environment ( shielded or deshielded) requires different amount of energy to bring them into resonance. • An NMR spectrum provides signal or peak representing the energy necessary to bring each nuclei into resonance.
- 5. WHY CARBON-13 NMR REQUIRED • 1H NMR spectroscopy is a powerful and useful tool for structural analysis. • It useless when portion of a molecule lack C-H bond example:-polychlorinated compounds such as chlordane, polycarbonyl compound such as croconic acid and compounds incorporating triple bonds( structure below orange colored carbons). • Carbon-13 are spread over a much wider range than 1H signals making it easier to identify and count individual nuclei.
- 6. NATURAL ABUNDANCE • The major isotope of carbon 12 has no spin so it is not possible to conduct a carbon NMR experiment. • Almost 1.1% of elemental carbon is the carbon 13 isotope, which has a spin I=1/2, so possible to conduct a carbon NMR experiment. • The two features of a carbon 13 NMR spectrum that provide the most structural information are the number of signals observed and the chemical shift of those signals.
- 7. CARBON-13, NUMBER OF SIGNALS • The number of signals in a carbon-13 spectrum gives the number of different types of carbon atoms in a molecules.
- 8. CARBON-13 CHEMICAL SHIFTS • Carbon-13 chemical shifts are mainly most affected by the electronegativity of groups attached to the carbon.
- 11. CHEMICAL SHIFTS OF CARBON-13 NMR
- 12. SPIN-SPIN SPLITTING • Carbon-13 NMR magnetically couple with attached protons and adjacent protons. N+1 rule is obeyed and also called as hetronuclear spin-spin splitting.
- 13. PROTON DECOUPLING • A common method used in determining a carbon -13 NMR spectrum is to irradiate all of the hydrogen nuclei in the molecules at the same time the carbon resonance are being measured. • This irradiation causes the protons to become saturated and they undergo rapid upward downward transition all occurring rapidly.
- 14. PROTON DECOUPLED
- 15. OFF RESONANCE DECOUPLING • The coupling between each carbon atom each hydrogen attached directly to it and thus the N+1 rule applies : a carbon with N number of protons gives a signal with N+1 peaks.
- 17. NUCLEAR OVER HAUSER ENHANCEMENT • Carbon atoms with hydrogen atoms directly attached are enhanced. The enhancement increases as more hydrogen are attached. this effect is called the nuclear over hauser enhancement(NOE). • The NOE helpful to determining which groups are nearby space. • The effect can be either positive or negative depending on which atom types are involved. In case of carbon-13 interacting with H1 the effect is positive so intensities of signals increases.
- 19. POLARIZATION TRANSFER EXPERIMENT- DEPT • It is useful method for determining the presence of primary, secondary and tertiary carbon atoms. • The DEPT experiment differentiates between CH, CH2 and CH3 groups by the angle parameter. • 45o angle gives all carbon with attached protons in phase. • 90o angles gives only CH groups. • 135o angles gives all CH and CH3 in a phase.CH2 signals appear as negative signals (below the baseline). • Signals from quaternary carbons and other carbons with no attached protons are always absent ( due to the lack of attached protons.)
- 22. ADVANTAGES OF CARBON-13 NMR • Carbon-13 NMR has elucidate organic and biochemical structures. • Carbon-13 NMR provides information about the backbone to molecules rather than periphery.
- 23. DISADVANTAGES OF CARBON- 13 NMR • Carbon-13 natural abundance is very low (1.1%). • Carbon-13 and hydrogen-1 I=1/2 so that coupling between them probably occur.
- 24. APPLICATION OF CARBON-13 NMR • C-13 which the signal intensities and helps in tracing the cellular metabolism. • C-13 nuclei are stable isotopes and hence it is not dangers to radiotracers. • And also used for quantification of drug purity to determination of the composition of high molecular weight synthetic polymers.
- 25. REFERENCE • Instrumental methods of chemical analysis book ( Gurdeep R.chatwal, sham K.anand ) • Quantitative chemical analysis book ( Vogel) • Instrumental analysis book ( Skoog fifth edition) • www.chemguide.co.uk • https://en.wikipedia.org • www.chemwiki.ucdavis.edu • www.chem.ch.huji.ac