IB Chemistry on Nuclear Magnetic Resonance (NMR) Spectroscopy

• 1. Tutorial on Nuclear magnetic resonanceSpectroscopy (NMR). Prepared by Lawrence Kok http://lawrencekok.blogspot.com

2. Electromagnetic Radiation and SpectroscopyElectromagnetic Radiation Interact with Matter (Atoms, Molecules) = SpectroscopyElectromagnetic Radiation RadiowavesInfra RedUV or visible Nuclear spin Molecular vibrationTransition of outer most valence electronsNuclear Magnetic ResonanceInfra Red Spectroscopy UV SpectroscopyAtomic AbsorptionSpectroscopySpectroscopy Organic structure determination Organic structure determination Quantification of metal ions MRI and body scanning Functional gp determination Detection of metal in various samples Measuring bond strength Measuring degree unsaturation in fat Measuring level of alcohol in breath 3. Nuclear Magnetic Resonance Spectroscopy (NMR)Nuclear Magnetic Resonance Spectroscopy (NMR) Involve nucleus (proton + neutron) NOT electrons Proton + neutrons = Nucleons Nucleons like electrons have spin and magnetic moment (acts like a tiny magnet) Nuclei with even number of nucleon (12C and 16O) Even number of proton and neutron NO net spin Nucleon spin cancel out each other Nucleus have NO overall magnetic moment NOT absorb radiowave radiation Spin cancel each other Nuclei with odd number of nucleon (1H, 13C, 19F, 31P)-Nucleon have net spin Nucleus have NET magnetic moment Absorb radiowave radiation Nuclei with net spin magnetic moment will interact with electromagnetic radiation/radio waves Nuclei have a spin associated with them (i.e., they act as if they were spinning about an axis) due to the spinassociated with their protons and neutrons. Nuclei are positively charged, their spin induces a magnetic field NMR spectroscopy does not work for nuclei with even number of protons and neutrons nuclei have no net spin. 4. Nuclear Magnetic Resonance Spectroscopy (NMR) Main features of HNMR Spectra 1. Number of different absorption peaks Number of different proton/chemical environment 2. Area under the peaks - Number of hydrogen in a particular proton/chemical environment (Integration trace)- Ratio of number of hydrogen in each environment 3. Chemical shift- Chemical environment where the proton is in- Spinning electrons create own magnetic field, creating a shielding effect- Proton which are shielded appear upfield. (Lower frequency for resonance to occur)- Proton which are deshielded appear downfield away. (Higher frequency for resonance to occur)- Measured in ppm () 4. Splitting pattern- Due to spin-spin coupling- The number of peak split is equal to number of hydrogen on neighbouring carbon +1 (n+1) peak NMR spectrum of CH3CH2BrChemical Shift Number of peaksSplitting patternArea under peaksChemical shifthttp://chemwiki.ucdavis.edu/Physical_Chemistry/Quantum_Mechanics/Atomic_Theory/Electrons_in_Atoms/Electron_Spin 5. Nuclear Magnetic Resonance Spectroscopy (NMR)Absence of External magnetic Field (EMF) The TWO nuclear spin have the same energy, (same energy level) 6. Nuclear Magnetic Resonance Spectroscopy (NMR)Absence of External magnetic Field (EMF) Presence of External Magnetic Field (EMF) The TWO nuclear spin have the same energy, (same energy level) The TWO nuclear spin split to TWO different energy level 7. Nuclear Magnetic Resonance Spectroscopy (NMR)Absence of External magnetic Field (EMF)Presence of External Magnetic Field (EMF) The TWO nuclear spin have the same energy, (same energy level) The TWO nuclear spin split to TWO different energy level Absence of EMF Two spins in same energy level 8. Nuclear Magnetic Resonance Spectroscopy (NMR)Absence of External magnetic Field (EMF)Presence of External Magnetic Field (EMF) The TWO nuclear spin have the same energy, (same energy level) The TWO nuclear spin split to TWO different energy level High spin nuclei align against magnetic fieldPresence of EMF E Two spins in different energy level Lower spin nuclei absorb radio frequency equivalent to E Move to higher energy level Absence of EMF Two spins in same energy level Lower spin nuclei align with magnetic field 9. Nuclear Magnetic Resonance Spectroscopy (NMR)Absence of External magnetic Field (EMF) Presence of External Magnetic Field (EMF) The TWO nuclear spin have the same energy, (same energy level) The TWO nuclear spin split to TWO different energy levelPresence of External Magnetic Field (EMF) External magnetic field applied to atomic nuclei, magnetic field of nuclei align themselves either with or against magnetic field Nuclei have a slight preference for the parallel alignment with the applied field as it has a slightly lower energy, Nuclei can absorb energy to move/flip to higher energy level by absorbing energy in radio frequency regionHigh spin nuclei align against magnetic fieldPresence of EMFE Two spins in different energy level Lower spin nuclei absorb radio frequency equivalent to E Move to higher energy levelAbsence of EMF Two spins in same energy levelLower spin nuclei align with magnetic field 10. Chemical Shift (Shielding Effect)Proton in nucleus have spin generate its magnetic field (MF)Electrons around nucleus have spin- also generate its magnetic fieldProtons shielded by MF produced by electrons will appear UPFIELDProtons deshielded by electron withdrawing gps will appear DOWNFIELDDownfieldUpfield 11. Chemical Shift (Shielding Effect)Proton in nucleus have spin generate its magnetic field (MF)Electrons around nucleus have spin- also generate its magnetic fieldProtons shielded by MF produced by electrons will appear UPFIELDProtons deshielded by electron withdrawing gps will appear DOWNFIELDDownfieldUpfield Presence of EMF Two spins in different energy level Lower spin nuclei absorb radio frequency equivalent to E Move to higher energy level Absence of EMF Two spins in same energy level 12. Chemical Shift (Shielding Effect)Proton in nucleus have spin generate its magnetic field (MF)Electrons around nucleus have spin- also generate its magnetic fieldProtons shielded by MF produced by electrons will appear UPFIELDProtons deshielded by electron withdrawing gps will appear DOWNFIELDDownfield Upfield Presence of EMF Two spins in different energy level Lower spin nuclei absorb radio frequency equivalent to E Move to higher energy level Without any SHIELDING EFFECTE Energy of E absorb by H to move to higher energy level Absence of EMFPresence of EMF Two spins in same energy level Two spins at diff energy level 13. Chemical Shift (Shielding Effect)Proton in nucleus have spin generate its magnetic field (MF)Electrons around nucleus have spin- also generate its magnetic fieldProtons shielded by MF produced by electrons will appear UPFIELDProtons deshielded by electron withdrawing gps will appear DOWNFIELDDownfield Upfield Presence of EMF Two spins in different energy level Lower spin nuclei absorb radio frequency equivalent to E Move to higher energy level Without any SHIELDING EFFECTE Energy of E absorb by H to move to higher energy level Absence of EMFPresence of EMF Two spins in same energy level Two spins at diff energy level Absence of EMF Two spins in same energy level 14. Chemical Shift (Shielding Effect)Proton in nucleus have spin generate its magnetic field (MF)Electrons around nucleus have spin- also generate its magnetic fieldProtons shielded by MF produced by electrons will appear UPFIELDProtons deshielded by electron withdrawing gps will appear DOWNFIELDDownfieldUpfield Presence of EMF Two spins in different energy level Lower spin nuclei absorb radio frequency equivalent to E Move to higher energy level Without any SHIELDING EFFECTE Energy of E absorb by H to move to higher energy level Absence of EMFPresence of EMF Two spins in same energy level Two spins at diff energy level SHIELDING EFFECT Electrons around H will produce MF and shield the H H in CH3 will experience less EMF (SHIELDED)E is smaller Absorb at lower radiofrequency to move to higher level E absorb by H to move to higher energy level is less Appear upfield. Absence of EMFPresence of EMF Two spins in same energy level Two spins at diff energy level 15. Chemical Shift (Deshielding Effect)Proton in nucleus have spin generate its magnetic field (MF)Electrons around nucleus have spin- also generate its magnetic fieldProtons shielded by MF produced by electrons will appear UPFIELDProtons deshielded by electron withdrawing gps will appear DOWNFIELDDownfieldUpfield 16. Chemical Shift (Deshielding Effect)Proton in nucleus have spin generate its magnetic field (MF)Electrons around nucleus have spin- also generate its magnetic fieldProtons shielded by MF produced by electrons will appear UPFIELDProtons deshielded by electron withdrawing gps will appear DOWNFIELDDownfieldUpfield Presence of EMF Two spins in different energy level Lower spin nuclei absorb radio frequency equivalent to E Move to higher energy level Absence of EMF Two spins in same energy level 17. Chemical Shift (Deshielding Effect)Proton in nucleus have spin generate its magnetic field (MF)Electrons around nucleus have spin- also generate its magnetic fieldProtons shielded by MF produced by electrons will appear UPFIELDProtons deshielded by electron withdrawing gps will appear DOWNFIELDDownfield Upfield Presence of EMF Two spins in different energy level Lower spin nuclei absorb radio frequency equivalent to E Move to higher energy levelE Without any DESHIELDING EFFECT Energy of E absorb by H to move to higher energy level Absence of EMFPresence of EMF Two spins in same energy level Two spins at diff energy level 18. Chemical Shift (Deshielding Effect)Proton in nucleus have spin generate its magnetic field (MF)Electrons around nucleus have spin- also generate its magnetic fieldProtons shielded by MF produced by electrons will appear UPFIELDProtons deshielded by electron withdrawing gps will appear DOWNFIELDDownfield Upfield Presence of EMF Two spins in different energy level Lower spin nuclei absorb radio frequency equivalent to E Move to higher energy levelE Without any DESHIELDING EFFECT Energy of E absorb by H to move to higher energy level Absence of EMFPresence of EMF Two spins in same energy level Two spins at diff energy level Absence of EMF Two spins in same energy level 19. Chemical Shift (Deshielding Effect)Proton in nucleus have spin generate its magnetic field (MF)Electrons around nucleus have spin- also generate its magnetic fieldProtons shielded by MF produced by electrons will appear UPFIELDProtons deshielded by electron withdrawing gps will appear DOWNFIELDDownfield Upfield Presence of EMF Two spins in different energy level Lower spin nuclei absorb radio frequency equivalent to E Move to higher energy levelE Without any DESHIELDING EFFECT Energy of E absorb by H to move to higher energy level Absence of EMFPresence of EMF Two spins in same energy level Two spins at diff energy level DESHIELDING EFFECT Electrons are withdrawn away by C=O gp Carbonyl gp has electron withdrawing effect Less electron around the H in CH3E is higher H in CH3 will be deshielded, experience greater EMF E absorb by H, to move to high energy level is higher Absorb at higher radiofreq, to move to high level Appear downfield Absence of EMFPresence of EMF Two spins in same energy level Two spins at diff energy level 20. Chemical Shift (Shielding and Deshielding Effect) Absence of EMFPresence of EMF Two spins in same energy level Two spins at diff energy levelNo shielding E Without any SHIELDING EFFECT Energy of E absorb by H to moveto higher energy level 21. Chemical Shift (Shielding and Deshielding Effect) Absence of EMFPresence of EMF Two spins in same energy level Two spins at diff energy levelDeshielding EffectDESHIELDING EFFECT Electrons are withdrawn away by C=O gp E is higher Carbonyl gp has electron withdrawing effect Less electron around the H in CH3 H in CH3 will be deshielded, experience greater EMF E absorb by H, to move to high energy level is higher Absorb at higher radiofreq, to move to high level Appear downfieldNo shielding E Without any SHIELDING EFFECT Energy of E absorb by H to moveto higher energy level 22. Chemical Shift (Shielding and Deshielding Effect) Absence of EMFPresence of EMF Two spins in same energy level Two spins at diff energy levelDeshielding EffectDESHIELDING EFFECT Electrons are withdrawn away by C=O gp E is higher Carbonyl gp has electron withdrawing effect Less electron around the H in CH3 H in CH3 will be deshielded, experience greater EMF E absorb by H, to move to high energy level is higher Absorb at higher radiofreq, to move to high level Appear downfieldNo shielding E Without any SHIELDING EFFECT Energy of E absorb by H to moveto higher energy levelShielding EffectSHIELDING EFFECT Electrons around H will produce MF and shield the H H in CH3 will experience less EMF (SHIELDED) Absorb at lower radiofrequency to move to higher level E is smaller E absorb by H to move to higher energy level is less Appear upfield. 23. Chemical Shift (Shielding and Deshielding Effect) Absence of EMFPresence of EMF Two spins in same energy level Two spins at diff energy levelDeshielding EffectDESHIELDING EFFECT Electrons are withdrawn away by C=O gp E is higher Carbonyl gp has electron withdrawing effect Less electron around the H in CH3 H in CH3 will be deshielded, experience greater EMF E absorb by H, to move to high energy level is higher Absorb at higher radiofreq, to move to high level Appear downfieldNo shielding E Without any SHIELDING EFFECT Energy of E absorb by H to moveto higher energy levelShielding EffectSHIELDING EFFECT Electrons around H will produce MF and shield the H H in CH3 will experience less EMF (SHIELDED) Absorb at lower radiofrequency to move to higher level E is smaller E absorb by H to move to higher energy level is less Appear upfield. Downfield Upfield 24. Chemical Shift (Shielding and Deshielding Effect)Shielding/Deshielding: Electron circulates nucleus, creates magnetic field opposing the external magnetic field. Hence, each nucleus experience a slightly different magnetic field (Sum of external field and field from the electron cloud). Energy a nucleus achieves resonance depends on its surroundings. Frequency absorption depend on electron density around nucleus (chemical environment)Chemical shift of various electron withdrawing groupsDownfieldUpfield Electron withdrawn from CH3 by C=O Deshield the H in CH3 Absorb at slightly higher radiofreq Upfield 2.1 25. Chemical Shift (Shielding and Deshielding Effect)Shielding/Deshielding: Electron circulates nucleus, creates magnetic field opposing the external magnetic field. Hence, each nucleus experience a slightly different magnetic field (Sum of external field and field from the electron cloud). Energy a nucleus achieves resonance depends on its surroundings. Frequency absorption depend on electron density around nucleus (chemical environment)Chemical shift of various electron withdrawing groupsDownfield Upfield Electron withdrawn from CH3 by C=O Deshield the H in CH3 Absorb at slightly higher radiofreq Upfield 2.1 Electron withdrawn from CH2 by COO Stronger electron withdrawing effect Higher Deshielding effect on H in CH2 Absorb at Higher radiofreq Slightly Downfield 4.1 26. Chemical Shift (Shielding and Deshielding Effect)Shielding/Deshielding: Electron circulates nucleus, creates magnetic field opposing the external magnetic field. Hence, each nucleus experience a slightly different magnetic field (Sum of external field and field from the electron cloud). Energy a nucleus achieves resonance depends on its surroundings. Frequency absorption depend on electron density around nucleus (chemical environment)Chemical shift of various electron withdrawing groupsDownfieldUpfield Electron withdrawn from CH3 by C=O Deshield the H in CH3 Absorb at slightly higher radiofreq Upfield 2.1 Electron withdrawn from CH2 by COO Stronger electron withdrawing effect Higher Deshielding effect on H in CH2 Absorb at Higher radiofreq Slightly Downfield 4.1 Electron withdrawn by benzene Stronger electron withdrawing effect Higher deshielding effect on H Absorb at Very high radiofreq Very Downfield 7.3 - 8 27. Chemical Shift (Shielding and Deshielding Effect)Shielding/Deshielding: Electron circulates nucleus, creates magnetic field opposing the external magnetic field. Hence, each nucleus experience a slightly different magnetic field (Sum of external field and field from the electron cloud). Energy a nucleus achieves resonance depends on its surroundings. Frequency absorption depend on electron density around nucleus (chemical environment)Chemical shift of various electron withdrawing groupsDownfield Upfield Electron withdrawn from CH3 by C=O Deshield the H in CH3 Absorb at slightly higher radiofreq Upfield 2.1 Electron withdrawn from CH2 by COO Stronger electron withdrawing effect Higher Deshielding effect on H in CH2 Absorb at Higher radiofreq Slightly Downfield 4.1 Electron withdrawn by benzene Stronger electron withdrawing effect Higher deshielding effect on H Absorb at Very high radiofreq Very Downfield 7.3 - 8 Electron withdrawn from H by CHO Very strong electron withdrawing effect Higher Deshielding effect on H in CHO Absorb at Very High radiofreq Very Very Downfield 9.7 28. Chemical Shift (Shielding and Deshielding Effect)Shielding/Deshielding: Electron circulates nucleus, creates magnetic field opposing the external magnetic field. Hence, each nucleus experience a slightly different magnetic field (Sum of external field and field from the electron cloud). Energy a nucleus achieves resonance depends on its surroundings. Frequency absorption depend on electron density around nucleus (chemical environment)Chemical shift of various electron withdrawing groupsDownfield Upfield Electron withdrawn from CH3 by C=O Deshield the H in CH3 Absorb at slightly higher radiofreq Upfield 2.1 Electron withdrawn from CH2 by COO Stronger electron withdrawing effect Higher Deshielding effect on H in CH2 Absorb at Higher radiofreq Slightly Downfield 4.1 Electron withdrawn by benzene Stronger electron withdrawing effect Higher deshielding effect on H Absorb at Very high radiofreq Very Downfield 7.3 - 8 Electron withdrawn by COOH Electron withdrawn from H by CHO Very strong electron withdrawing effect Very strong electron withdrawing effect Highest deshielding effect on H Higher Deshielding effect on H in CHO Absorb at Very High radiofreq Absorb at Very High radiofreq Very Very Very Downfield 12 Very Very Downfield 9.7 29. Nuclear Magnetic Resonance Spectroscopy (NMR)HO-CH2-CH3OHCH2 CH3 chemical shift 4.8 chemical shift 3.8 chemical shift 1 integration = 1 H integration = 2 H integration = 3 H No split (Singlet) split into 4 split into 3 1 2312UpfieldDownfield 3 different proton environment Ratio of 3:2:1 30. Nuclear Magnetic Resonance Spectroscopy (NMR)HO-CH2-CH3OHCH2 CH3 chemical shift 4.8 chemical shift 3.8 chemical shift 1 integration = 1 H integration = 2 H integration = 3 H No split (Singlet) split into 4 split into 3 1 2312UpfieldDownfield 3 different proton environment Ratio of 3:2:1 Tetramethyl Silane (TMS) as STD Strong peak upfield (shielded) Silicon has lower EN value < carbon Electron shift to carbon H in CH3 will be more shielded Experience lower EMF, absorb radiofrequancy UPFIELD 0 31. Nuclear Magnetic Resonance Spectroscopy (NMR)HO-CH2-CH3OHCH2CH3 chemical shift 4.8 chemical shift 3.8 chemical shift 1 integration = 1 H integration = 2 H integration = 3 H No split (Singlet) split into 4 split into 3 1 2 3 12Upfield Downfield 3 different proton environment Ratio of 3:2:1 Tetramethyl Silane (TMS) as STD Strong peak upfield (shielded) Silicon has lower EN value < carbon Electron shift to carbon H in CH3 will be more shielded Experience lower EMF, absorb radiofrequancy UPFIELD 0Advantages using TMS Volatile and can be removed from sample All 12 hydrogens are in the same proton environment Single strong peak, upfield, doesnt interfere with other peaks All chemical shift, measured in ppm () are relative to thisSTD, taken as zeroClick here for more complicated proton chemical shift 32. NMR SpectrumOCH3-C-O-CH2-CH3 B A C 2 3 3 3 diff proton enviroment, Ratio H - 3:2:3 Peak A split to 3 2H on neighbour C Peak B - No split Peak C split to 4 3H on neighbour C O HO-C-CH2-CH3 ABC 12312 3 diff proton enviroment, ratio H - 3:2:1 Peak A split to 3 2H on neighbour C Peak B split to 4 3H on neighbour C Peak C No split 33. NMR Spectrum HO-CH2-CH3ABC3213 diff proton enviroment, Ratio H - 3:2:1 Peak A split to 3 2H on neighbour C Peak B split to 4 3H on neighbour C Peak C No splitO CH3-C-CH2-CH2-CH3ADCB232 34 diff proton enviroment, Ratio H - 3:2:2:3 Peak A split to 3 2H on neighbour C Peak B split to 6 5H on neighbour C Peak C No split Peak D split to 3 2H on neighbour C 34. NMR SpectrumO CH3-C-O-CH2-CH2-CH3AD C B2 3 2 34 diff proton enviroment, Ratio H 3:2:2:3 Peak A split to 3 2H on neighbour C Peak B split to 6 5H on neighbour C Peak C No split Peak D split to 3 2H on neighbour C O H-C-CH3AB319.82 diff proton enviroment, Ratio H - 3:1 Peak A split to 2 1H on neighbour C Peak B split to 4 3H on neighbour C 35. NMR SpectrumCH3Molecule with plane of symmetry |H-C-OH|CH3 C A B11 63 diff proton enviroment, Ratio H - 6:1:1 Peak A split to 2 1H on neighbour C Peak B No split Peak C split to 7 6H on neighbour C O CH3Molecule with plane of symmetry| CH3-C-O-CH|CH3 ABC1 36 3 diff proton enviroment, Ratio H - 6:3:1 Peak A split to 2 1H on neighbour C Peak B No split Peak C split to 7 6H on neighbour C 36. NMR SpectrumOMolecule with plane of symmetryCH3-CH2-C-CH2-CH3 A B 4 6 2 diff proton enviroment, Ratio H 6:4 Peak A split to 3 2H on neighbour C Peak B split to 4 3H on neighbour C O CH3Molecule with plane of symmetry | H-C-C-CH3 A | CH3 B 9 1 2 diff proton enviroment, Ratio H 9:1 Peak A No split Peak B No split 37. NMR SpectrumCH3Molecule with plane of symmetry| HO-CH2-CH|ACH3B DC 2 11 64 diff proton enviroment, Ratio H 6:1:1:2 Peak A split to 2 1H on neighbour C Peak B split to 7 6H on neighbour C Peak C No split Peak D split to 2 1H on neighbour CCH3-CH-CH3Molecule with plane of symmetry| CIAB 162 diff proton enviroment, Ratio H 6:1 Peak A split to 2 1H on neighbour C Peak B split to 7 6H on neighbour C 38. IR Spectra search for different Organic MoleculesClick here to animated SpectraClick here to search IR spectra 39. AcknowledgementsThanks to source of pictures and video used in this presentationThanks to Creative Commons for excellent contribution on licenseshttp://creativecommons.org/licenses/Prepared by Lawrence KokCheck out more video tutorials from my site and hope you enjoy this tutorialhttp://lawrencekok.blogspot.com