Chapter 13 Spectroscopy13.1 Principles of Molecular Spectroscopy: Electromagnetic RadiationElectromagnetic RadiationFigure 13.1: The Electromagnetic SpectrumSlide 5Slide 613.2 Principles of Molecular Spectroscopy: Quantized Energy StatesDE = hnWhat Kind of States?13.3 Introduction to 1H NMR SpectroscopyThe nuclei that are most useful to organic chemists are:Nuclear SpinThe distribution of nuclear spins is random in the absence of an external magnetic field.An external magnetic field causes nuclear magnetic moments to align parallel and antiparallel to applied field.There is a slight excess of nuclear magnetic moments aligned parallel to the applied field.Energy Differences Between Nuclear Spin StatesSome important relationships in NMRSlide 18Slide 19Slide 2013.4 Nuclear Shielding and 1H Chemical ShiftsShieldingSlide 23Slide 24Chemical ShiftPowerPoint PresentationSlide 2713.5 Effects of Molecular Structure on 1H Chemical ShiftsElectronegative substituents decrease the shielding of methyl groupsSlide 30Effect is cumulativeProtons attached to sp2 hybridized carbon are less shielded than those attached to sp3 hybridized carbonTable 13.1 (p 496)Slide 34Slide 35Chapter 13Chapter 13SpectroscopySpectroscopyInfrared spectroscopyInfrared spectroscopyUltraviolet-Visible spectroscopyUltraviolet-Visible spectroscopyNuclear magnetic resonance spectroscopyNuclear magnetic resonance spectroscopyMass SpectrometryMass Spectrometry13.113.1Principles of Molecular Principles of Molecular Spectroscopy:Spectroscopy:Electromagnetic RadiationElectromagnetic Radiationis propagated at the speed of lightis propagated at the speed of lighthas properties of particles and waveshas properties of particles and wavesthe energy of a photon is proportional the energy of a photon is proportional to its frequencyto its frequencyElectromagnetic RadiationElectromagnetic RadiationElectromagnetic RadiationElectromagnetic RadiationFigure 13.1: Figure 13.1: The Electromagnetic SpectrumThe Electromagnetic SpectrumFigure 13.1: Figure 13.1: The Electromagnetic SpectrumThe Electromagnetic Spectrum400 nm400 nm750 nm750 nmVisible LightLonger Wavelength (Longer Wavelength ())Shorter Wavelength (Shorter Wavelength ())Higher Frequency (Higher Frequency ())Lower Frequency (Lower Frequency ())Higher Energy (Higher Energy (EE))Lower Energy (Lower Energy (EE))Figure 13.1: Figure 13.1: The Electromagnetic SpectrumThe Electromagnetic SpectrumFigure 13.1: Figure 13.1: The Electromagnetic SpectrumThe Electromagnetic SpectrumLonger Wavelength (Longer Wavelength ())Shorter Wavelength (Shorter Wavelength ())Higher Frequency (Higher Frequency ())Lower Frequency (Lower Frequency ())Higher Energy (Higher Energy (EE))Lower Energy (Lower Energy (EE))UltravioletUltravioletInfraredInfraredCosmic raysCosmic rays RaysRaysX-raysX-raysUltraviolet lightUltraviolet lightVisible lightVisible lightInfrared radiationInfrared radiationMicrowavesMicrowavesRadio wavesRadio wavesCosmic raysCosmic rays RaysRaysX-raysX-raysUltraviolet lightUltraviolet lightVisible lightVisible lightInfrared radiationInfrared radiationMicrowavesMicrowavesRadio wavesRadio wavesFigure 13.1: Figure 13.1: The Electromagnetic SpectrumThe Electromagnetic SpectrumFigure 13.1: Figure 13.1: The Electromagnetic SpectrumThe Electromagnetic SpectrumEnergyEnergy13.213.2Principles of Molecular Spectroscopy: Principles of Molecular Spectroscopy: Quantized Energy StatesQuantized Energy StatesElectromagnetic radiation is absorbed when theElectromagnetic radiation is absorbed when theenergy of photon corresponds to difference in energy of photon corresponds to difference in energy between two states.energy between two states.E = hE = hE = hE = helectronicelectronicvibrationalvibrationalrotationalrotationalnuclear spinnuclear spinUV-VisUV-VisinfraredinfraredmicrowavemicrowaveradiofrequencyradiofrequencyWhat Kind of States?What Kind of States?What Kind of States?What Kind of States?13.313.3Introduction to Introduction to 11H NMR SpectroscopyH NMR Spectroscopy11H and H and 1313CCboth have spin = ±1/2both have spin = ±1/211H is 99% at natural abundanceH is 99% at natural abundance1313C is 1.1% at natural abundanceC is 1.1% at natural abundanceThe nuclei that are most useful toThe nuclei that are most useful toorganic chemists are:organic chemists are:The nuclei that are most useful toThe nuclei that are most useful toorganic chemists are:organic chemists are:Nuclear SpinNuclear SpinNuclear SpinNuclear SpinA spinning charge, such as the nucleus of A spinning charge, such as the nucleus of 11H H or or 1313C, generates a C, generates a magnetic fieldmagnetic field. The . The magnetic field magnetic field generated by a nucleus of spin generated by a nucleus of spin +1/2 is opposite in direction from that +1/2 is opposite in direction from that generated by a nucleus of spin –1/2.generated by a nucleus of spin –1/2. +++++++ The distribution of The distribution of nuclear spins is nuclear spins is random in the random in the absence of an absence of an external magnetic external magnetic field.field.+++++An external magnetic An external magnetic field causes nuclear field causes nuclear magnetic moments to magnetic moments to align parallel and align parallel and antiparallel to applied antiparallel to applied field.field.HH00++++ +There is a slight There is a slight excess of nuclear excess of nuclear magnetic moments magnetic moments aligned parallel to aligned parallel to the applied field.the applied field.HH00no difference in absence of magnetic fieldno difference in absence of magnetic fieldproportional to strength of external magnetic field proportional to strength of external magnetic field Energy Differences Between Nuclear Spin StatesEnergy Differences Between Nuclear Spin StatesEnergy Differences Between Nuclear Spin StatesEnergy Differences Between Nuclear Spin States ++ EEE E ''increasing field strengthincreasing field strengthSome important relationships in NMRSome important relationships in NMRSome important relationships in NMRSome important relationships in NMRThe frequency of absorbedThe frequency of absorbedelectromagnetic radiationelectromagnetic radiationis proportional tois proportional tothe energy difference betweenthe energy difference betweentwo nuclear spin statestwo nuclear spin stateswhich is proportional towhich is proportional tothe applied magnetic