Chapter 14: 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:14.1 Introduction to NMR Spectroscopy14.2 Fourier Transform NMR14.3 Shielding*14.4 The Number of Signals in the 1H NMR Spectrum*14.5 The Chemical Shift*14.6 The Relative Position of 1H NMR Signals*14.7 Characteristic Values of Chemical Shifts*14.8 Integration of NMR Signals*14.9 Diamagnetic Anisotropiy14.10 Splitting of the Signals*14.11 More Examples of 1H NMR Spectra*14.12 Coupling Constants*14.13 Splitting Diagrams*14.14 Time Dependence of NMR Spectroscopy14.15 Protons Bonded to Oxygen and Nitrogen*14.16 Use of Deuterium in 1H NMR Spectroscopy#14.17 Resolution of 1H NMR Spectra14.18 13C NMR Spectroscopy*14.19 DEPT 13C NMR Spectra#14.20 Two-dimensional NMR Spectroscopy#* Sections that will be focused# Sections that will be skipped 1Recommended additional problems41 – 61, 63 – 71Class Note14.1 Introduction to NMR Spectroscopy and 14.2 Fourier Transform NMR14.3 ShieldingcapNMR tubesampleApplied magnetic fieldHHHupfielddownfield2intensityDeshielded (low electron density)Shielded (high electron density)14.4 The Number of Signals in the 1H NMR Spectrum*Judge the chemically equivalent of H by the symmetry of moleculeH HHHHHHHH ClHHHHHHH HHHHHHClClHHHHHHHHHHHHCH3ClHHBrHHClHNO2HHHClHClHHHClNO2HHHHHHHBrHHHHHHHHClHHHHHHH314.5 The Chemical Shift, 14.6 The Relative Position of 1H NMR Signals, and 14.9 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)H7.314.7 Characteristic Values of Chemical ShiftsTable 14.114.8 Integration of NMR Signals* Diagnostic for 1H NMR but less accurate for 13C NMR* Ratio rather than exact numberH ClHHHHHHH HHHHHHClHaHbHcHaHbHHHHHHHHHHOHaHaHbHbIIIIII614.10 Splitting of the SignalsA. 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 HHHHHHClHaHbHcHaHbHHHHHHHHHHOHaHaHbHbIIIIII814.11 More Examples of 1H NMR SpectraA. More examplesBr BrHHHHHHHbHaH3CHHHHO HCH3H3COHaHbHcHdIVVHbHe9B. Difference between quartet (q) and doublet of doublet (dd)Cl BrClHOCH3HBrHHHHClHO HHHOHaHbVIVIIHaHbHcHc1014.12 Coupling Constants and 14.13 Splitting DiagramsA. 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)1414.15 Protons Bonded to Oxygen and Nitrogen and 14.16 Use of Deuterium in 1H NMR Spectroscopy14.17 Resolution of 1H NMR Spectra60 MHz 90 MHz300 MHz 400 MHz600 MHz1H NMR1514.18 13C NMR SpectroscopyA. Table 14.4Chemical shift and height (intensity)B. Proton-coupled and proton-decoupled 13C