Structure Determination by NMR.doc
《Structure Determination by NMR.doc》由会员分享,可在线阅读,更多相关《Structure Determination by NMR.doc(105页珍藏版)》请在得力文库 - 分享文档赚钱的网站上搜索。
1、40-042 Analytische Chemie IVStructure Determination byNMRProf. Bernhard JaunOffice: ETH Hnggerberg HCI E317Phone: 01 632 31 44e-mail: jaunorg.chem.ethz.chhome page: http:/www.jaun.chem.ethz.chProf. B. Jaun: Structure determination by NMR / Analytische Chemie IV2Contents1.Practical aspects of pulse F
2、ourier transform NMR spectroscopy1.1The basic NMR experiment: physical description1.2Excitation by RF pulses1.3Digitization, window functions and fourier transform1.4Quadrature detection1.5Phase cycles and Z-gradients1.6Dynamic range and solvent suppression1.7The principal components of an NMR spect
3、rometer2.The principle of 2D-NMR2.1The basic idea2.2A meaningless experiment2.3Quadrature detection in 13.Homonuclear shift correlation through scalar couplings3.1COSY.3.2Determination of coupling constants from COSY cross peaks.3.3TOCSY3.4INADEQUATE: homonuclear 13C-13C double quantum spectroscopy.
4、4.Spectral editing4.1Spin echo building blocks4.2Heteronuclear J-modulation4.3Polarisation transfer: INEPT and DEPT5.Heteronuclear shift correlation through one bond and long range couplings5.1Proton detected methods5.2Proton detected H,X-COSY5.3HSQC and HMQC5.4HMBCProf. B. Jaun: Structure determina
5、tion by NMR / Analytische Chemie IV36.Relaxation, dipole-dipole couplings and NOE6.1Longitudinal and transversal relaxation6.2NOE in a two spin system without scalar coupling6.3The mechanism of dipolar relaxation7.Homonuclear 1D-NOE difference spectroscopy7.1The steady state NOE in homonuclear multi
6、-spin systems7.2Practice of 1D-NOE difference spectroscopy8.Kinetic NOE-spectroscopy8.1NOESY8.2NOE in the rotating frame: ROESY9.On the influence of dynamic processes on NOE spectra9.1Overall molecular tumbling, internal rotation (conformational changes) und chemical exchange9.2How to proceed with m
7、olecules with 0c near 110.Combined application of several methods10.1 Typical structure problems with organic molecules and suitable strategies11.References and additional reading11.1 Textbooks11.2 Homonuclear correlation through scalar coupling11.3 Heteronucleare correlation through scalar coupling
8、11.4 NOE11.5 Coupling constants und Karplus relationships11.6 Abbreviations and Acronyms11.7 On the presentation of 2D-NMR data in the experimental part of a thesis or publication.Prof. B. Jaun: Structure determination by NMR / Analytische Chemie IV4What we would like to achieve with this course:-Th
9、e student knows which method yields which type of structural information.-The student is able to choose the most promising combination of methods for the solution of a given structural problem. Since spectrometer capacity is expensive, the selection of an optimal strategy depends on technical (feasi
10、bility) as well as on economical (fast and simple) factors.-The student knows how to interpret each type of spectrum and how to extract the pertinent data.-The student is aware of the possible artifacts and errors of interpretation for each method.-The student knows the NMR vocabulary and is able to
11、 correctly describe NMR data in publications.Subjects that are not part of this course:-Comprehensive treatment of the underlying theory (quantum mechanics of NMR)(- courses by Prof. Schweiger and Meier).- Solid state NMR-Practical nuts and bolts of carrying out the measurements on the spectrometer.
12、(- Praktikum Analytische Chemie)-Application to large biopolymers such as proteins and nucleic acids (- course by Prof. Wthrich) and calculation methods (simulated annealing, distance geometry etc.) usedto derive solution structures of biopolymers from NMR data. Shorter oligopeptides, oligonucleotid
13、es und oligosaccharides, however, will be discussed as examples or problems.Outline of the course:-Lectures on the individual methods with discussion of example spectra.-Problems (real life spectra) for each of the discussed methods.-Problems on structure elucidation of medium to complex organic mol
14、ecules with combined methods (in the last ca. 1/3) of the course.Prof. B. Jaun: Structure determination by NMR / Analytische Chemie IV1.11.Practical aspects of pulse Fourier transform NMR spectroscopy1.1 The basic NMR experiment: physical descriptionSpinComponent of the angular momentum of nuclei, e
15、lectrons (and other elementary particles) that cannotbe described as orbital momentum. Its origin is only understandable in terms of relativistic quantum mechanics.The magnetic momentThe magnetic moment () associated with the orbital angular momentum (L) of a charged particle is given by: L = r x pL
16、pe-r = LThe spin angular momentum Jis associated with a magnetic moment as well:J= , the gyromagnetic ratio is a fundamental property of each nuclear isotope with non-zero spinInteraction between the magnetic moment und an external magnetic fieldClassical physics:zB0The torque T acts on . In respons
17、e, precesses around the direction of B 0 (analogousto a spinning top under the force of gravity) with the circular frequency 0 rad/s, which is called the Larmor frequency. T = x B00Ty0 = B 0x Epot = - . B0Prof. B. Jaun: Structure determination by NMR / Analytische Chemie IV1.2Quantum mechanics: Quan
18、tum mechanical description of the spin angular momentum J : J = h II : nuclear spin operatorI : spin quantum number of the nucleus, a property of each isotope (I = 1/2.n; n=0,1,2).a)The z-component (parallel to the external field) of the spin angular momentum can only assume certain values governed
19、by the magnetic quantum number mI :J = h mm = - I, - I + 1,.,0, I - 1, Im magnetic quantum numberzIIIThis leads to 2I+1 allowed states. For nuclei with I = 1/2, which are of predominant interest in organicchemistry, only the two states with mI = -1/2 and mI = +1/2 are possible.The interaction energy
20、 for each state with a static external magnetic field along the z-axis isE = - z . B0 = - J z B0E = - h mI B0The energy difference between the two states is:E = - (1/2 - (- 1/2) B0= - B0In order to achieve resonance, the energy of the irradiated radio frequency has to match the energydifference betw
21、een the two states:E = h = = - B0The Larmor (circular) frequency is: i = - (1-i)B0zWith I = resonance frequency (rad/s) of spin i with shielding constant iThe resonance frequency for a given isotope is proportional to the gyromagnetic ratio and to the external magnetic field.a) The spin quantum numb
22、ers of nuclei follow the rules:A = Z + NA = mass numberZ = number of protons(nuclear charge)N = number of neutronsA even - I = integerZ even, N even - I=0Z odd, N odd - I=1,2,3. A odd - I= 1/2, 3/2, 5/2 .Prof. B. Jaun: Structure determination by NMR / Analytische Chemie IV1.3Macroscopic magnetizatio
- 配套讲稿:
如PPT文件的首页显示word图标,表示该PPT已包含配套word讲稿。双击word图标可打开word文档。
- 特殊限制:
部分文档作品中含有的国旗、国徽等图片,仅作为作品整体效果示例展示,禁止商用。设计者仅对作品中独创性部分享有著作权。
- 关 键 词:
- Structure Determination by NMR
限制150内