Chapter 13: NMR SpectroscopyLearning Objectives:1. Know how nuclear spins are affected by a magnetic field, and be able to explainwhat happens when radiofrequency radiation is absorbed.2. Be able to predict the number of proton and carbon NMR signals expected from acompound given its structure.3. Be able to predict the splitting pattern in the proton NMR spectrum of a compoundgiven its structure.4. With the aid of a chart of chemical shifts from 1H and 13C NMR, be able to assignpeaks in an NMR spectrum to specific protons in a compound.5. Be able to interpret integration of NMR spectra.6. Be able to use NMR spectra to determine the structures of compounds, given otherinformation such as a molecular formula.7. Be able to calculate coupling constants from 1H NMR spectra, and utilize the coupling constants for determining compound structure.*8. Be able to determine the compound structure based on information generated from mass spectrometry, IR, NMR, and elemental analysis.** Supplemental material, not included in the textbookSections:13.1 An Introduction to NMR Spectroscopy13.2 Fourier Transform NMR13.3 Shielding Causes Different Hydrogens to Show Signals at Different Frequencies*13.4 The Number of Signals in an 1H NMR Spectrum*13.5 The Chemical Shift Tells How Far the Signals Is from the Reference Signal*13.6 The Relative Position of 1H NMR Signals*13.7 Characteristic Values of Chemical Shifts*13.8 Diamagnetic Anisotropiy13.9 Integration of NMR Signals Reveals the Relative Number of Protons Causing the Signal*13.10 Splitting of the Signals Is Described by the N+1 Rule*13.11 More Examples of 1H NMR Spectra*13.12 Coupling Constants Identify Coupled Protons*13.13 Splitting Diagrams Explain the Multiplicity of a Signal*13.14 Diastereotopic Hydrogens Are Not Chemically Equivalent13.15 The Time Dependence of NMR Spectroscopy13.16 Protons Bonded to Oxygen and Nitrogen*13.17 The Use of Deuterium in 1H NMR Spectroscopy#13.18 Resolution of 1H NMR Spectra13.1913C NMR Spectroscopy*13.20 DEPT 13C NMR Spectra#13.21 Two-dimensional NMR Spectroscopy#13.22 NMR Used in Medicines Is Called Magnetic Resonance Imaging1* Sections that will be focused# Sections that will be skipped Recommended additional problems43 – 63, 65 – 72Class Note13.1 An Introduction to NMR Spectroscopy and 13.2 Fourier Transform NMR13.3 Shielding Causes Different Hydrogens to Show Signals at Different Frequencies*capNMR tubesampleApplied magnetic fieldHHHupfielddownfield2intensityDeshielded (low electron density)Shielded (high electron density)13.4 The Number of Signals in an 1H NMR Spectrum**Judge the chemically equivalent of H by the symmetry of moleculeH HHHHHHHH ClHHHHHHH HHHHHHClClHHHHHHHHHHHHCH3ClHHBrHHClHNO2HHHClHClHHHClNO2HHHHHHHBrHHHHHHHHClHHHHHHH313.5 The Chemical Shift Tells How Far the Signals Is from the Reference Signal*, 13.6 The Relative Position of 1H NMR Signals* and 13.8 Diamagnetic AnisotropiyInternal reference compound: CHCl3 (from CDCl3) and (CH3)4Si (TMS)*Signal of TMS = 0 ppm (CHCl3 = 7.27 ppm)*Chemical shift ()A. Effect from electronegativity (inductive effect)H ClHHHHHHH HHHHHHCl4B. Effect from resonanceOOOO6.157.634.92OCH3HHHHHOCH3HHHHHOCH3HHHHHOCH3HHHHH6.887.266.92C. Effect from structureOOOO2.544.732.723.751.853.521.515D. Diamagnetic Anisotropiy (anisotropic effect)Happlied magnetic field (Bo)induced magnetic field (Bi)actual magnetic field (Bo + Bi)H7.313.7 Characteristic Values of Chemical Shifts*Table 13.113.9 Integration of NMR Signals Reveals the Relative Number of Protons Causing the Signal** Diagnostic for 1H NMR but less accurate for 13C NMR* Ratio rather than exact numberH ClHHHHHHH HHHHHHClHaHbHcHaHbHHHHHHHHHHOHaHaHbHbIIIIII613.10 Splitting of the Signals Is Described by the N+1 Rule*A. Multiplicity of Signal and Relative IntensitiesRatio Multiplicity1 : 1 doublet1 : 2 : 1 triplet1 : 3 : 3 : 1 quartet1 : 4 : 6 : 4 : 1 quintet1 : 5 : 10 : 10 : 5 : 1 sextet1 : 6 : 15 : 20 : 15 : 6 : 1 septet1st splitting2nd splitting3rd splitting4th splitting5th splitting6th splittingOriginal signal11111111111123346 45 1010 561520156Two important criteria:* For I = 1/2* For chemically equivalent nuclei7B. ExamplesH ClHHHHHHH HHHHHHClHaHbHcHaHbHHHHHHHHHHOHaHaHbHbIIIIII813.11 More Examples of 1H NMR Spectra*A. More examplesBr BrHHHHHHHbHaH3CHHHHO HCH3H3COHaHbHcHdIVVHbHe9B. Difference between quartet (q) and doublet of doublet (dd)Cl BrClHOCH3HBrHHHHClHO HHHOHaHbVIVIIHaHbHcHc1013.12 Coupling Constants Identify Coupled Protons* and 13.13 Splitting Diagrams Explain the Multiplicity of a Signal*A. Table 14.3 and handoutB. Calculation of coupling constant (J value)3.2 ppm3.3 ppm15 mm5 mm2.5 mm400 MHz 1H NMRintegral ratio of peaks:1:3:3:13.2 ppm3.3 ppm15 mm5 mm2.5 mm400 MHz 1H NMRintegral ratio of peaks:1:1:1:1pattern Apattern B11C. Splitting diagrams and J values(1)HbHaHcJab = Jac(1)Jab > Jac(2)(2) long range coupling (4 bonds)12D. Structure determination and J values (1) Example 1COCH3HcHbHaJab = 2 HzJac = 15 HzJbc = 7 Hz(2) Example 2: determination of cis and trans isomersCOCH3HbH3CHaJab = 15 Hz or 7 HzHbCOCH3H3CHatranscis13(3) Example 3: determination of the regioisomers of di-substituted benzene derivativesBrNH2HHHHHNH2HBrHHHNH2BrHHH1,2-di-substituted(ortho)1,3-di-substituted(meta)1,4-di-substituted(para)1413.14 Diastereotopic Hydrogens Are Not Chemically EquivalentHBrHHHHHH13.15 The Time Dependence of NMR SpectroscopyFigure 13.29HHHH1513.16 Protons Bonded to Oxygen and Nitrogen* and 13.17 The Use of Deuterium in 1H NMR Spectroscopy#13.18 Resolution of 1H NMR Spectra60 MHz 90 MHz300 MHz 400 MHz600 MHz1H NMR1613.1913C NMR Spectroscopy*A. Table 13.4Chemical shift and height (intensity)B. Proton-coupled and proton-decoupled 13C spectra1713.22 NMR Used in Medicines Is Called Magnetic Resonance