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NCSU CH 221 - 221cam8-L9-skeletal

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11Lecture objectivesThis presentation’s objectives:©Dr. Kay Sandberg1) Examine the chemist’s use of various characterization tools2) Introduce 3 types of spectroscopy3) Examine the theory behind NMR spectroscopySpectroscopy & spectrometrySpectroscopy & spectrometry: techniques used to give evidence of the structure identification.How does a chemist prove that he/she synthesized a certain product? We can’t see individual molecules.2C-13 NMR samplereagent+Reactant1-propanol 2-propanol010203040506070PPM010203040506070PPM13C NMR spectraOHOH3Energy absorptionmoleculeSection 13.2What happens to the energythat gets absorbed by the molecule?lower energy state (E1)higher energy state (E2)before zaplower energy state (E1)higher energy state (E2)after zapΔE ΔE= E2- E1©Dr. Kay Sandberg4Delta EmoleculeSection 13.2lower energy state (E1)higher energy state (E2)before zaplower energy state (E1)higher energy state (E2)after zapΔE ΔEOnly radiation whose photon has energy equal to the ΔE gets absorbed - all other is transmitted©Dr. Kay Sandberg5ResonanceSection 13.2ΔE = Ephoton= hνphotonlower energy state (E1)higher energy state (E2)Only radiation whose photon has energy equal to the ΔE gets absorbed - all other is transmittedΔEin _________= E2- E1©Dr. Kay Sandberg63 spectroscopiesSection 13.2energy statesradio waves, infrared, light, or UVNMR(nuclear magnetic resonance)IR(infrared)UV-Vis(ultraviolet-visible)difference between_________ statesdifference between_________ statesdifference between________ states©Dr. Kay Sandberg____ ~ NMR27Delta E of 3 spectroscopiesSection 13.2radio waves, infrared, light, or UVenergy statesNMR IR UV-Visdifference betweennuclear spin statesdifference betweenvibrational statesdifference betweenelectronic states1E2EΔE1E2EΔE1E2EΔEGPYRed martiansinvaded Venus using X-ray gunsradiomicrowave infrared Visible light ultraviolet X-ray gamma___ E___ E©Dr. Kay Sandberg8Spectroscopy experimentradiation sourcesampledetector% transmittancewavelength, or frequency1000ROYGBIV ROYGBIV% absorbancewavelength, or frequency1000What is thephysical basisfor thesespectroscopies?©Dr. Kay SandbergChapter 139Hydrogen isotopeslike an electron, (QN +1/2 or -1/2)NMR –Nuclear Magnetic Resonance Spectroscopy©Dr. Kay Sandberg13C & 1H both have nuclear magnetic spin states of +1/2 and -1/21H•possesses ___ proton and ____ neutrons•hydrogen isotope, _______•the most abundant isotope of H•hydrogen isotope, __________ (D)2H3H •hydrogen isotope, tritiumChapter 1310Carbon isotopesChapter 13like an electron, (QN +1/2 or -1/2)NMR –Nuclear Magnetic Resonance Spectroscopy©Dr. Kay Sandberg13C & 1H both have nuclear magnetic spin states of +1/2 and -1/213C•possesses _ protons and _ neutrons•carbon isotope•less abundant isotope of C (only 1.1%)•most abundant isotope of C12C•______________19F & 31P also have nuclear spin states of +1/2 and -1/2.11Nuclear spinsIn the absence ofan external magneticfield there is nothingto orient spins &E = E+1/2 -1/2Section 13.3like an electron, certain nuclei have magnetic spin (QN +1/2 or -1/2)NMR (13C & 1H) both have nuclear magnetic spin states of +1/2 and -1/2+++++++++©Dr. Kay Sandberg12Nuclear spins in a magnetic fieldIn the presence of an external magnetic field (Ho)the spins are oriented.Section 13.3nuclear spin states+++++++++Hoeither parallel or antiparallel+1/2E-1/2EΔE©Dr. Kay SandbergNMR (13C & 1H)313NMR techniqueSection 13.3random nuclear spinswith equal energy spin states(no external magnetic field)apply external magnetic field(Ho)Hozap withradiofrequencyphotonΔE= hνphoton-1/2EΔE+1/2E+1/2E-1/2EΔEDetector:E absorbance©Dr. Kay Sandberg4.7 T (T = Tesla)14ProportionalitiesSection 13.3Frequency ofelectro-magneticradiation(s-1or Hz)is proportional toEnergy differencebetween nuclearspin states(kJ/mol)is proportional toMagneticfield(T)If a magnetic field strength of 4.7 T requires radiofrequency of 200 MHz to achieve resonance with the nuclei(i.e. for the spin flips to occur), would a 300 MHz radio frequency NMR instrument need a magnetic field higher or lower than 4.7 T?©Dr. Kay Sandberg15Field strengths and energy gapsSection 13.3+1/2E-1/2EΔEapply external magnetic field(Ho)Ho+1/2E-1/2EΔEapply strongerexternal magnetic field(H’o)H’o©Dr. Kay Sandberg200 MHz600 MHz16Field strength and energy gapsSection 13.3+1/2E-1/2EΔEenergy, Eincreasing magnetic field, Ho0ΔE = 0 in the absence of Ho60, 100, or 200 MHz(radio frequency)= Ephoton= hνphoton©Dr. Kay Sandberg17Induced fieldSection 13.4Is the magneticfield “felt” by thenuclear spingreater or lessthan the appliedexternal field?nucleus (nuclear spin)electron circulationinduced field felt by the nuclear spin(created by electron circulation, He)HoHe_________ HoNuclear spins are within molecules©Dr. Kay Sandberg18FieldsSection 13.4Hp= Ho- Henuclear spininduced fieldHoHe_______ Homagnetic field“felt” by nuclearspin(_____)externalmagnetic field(______)opposing e-induced field(_____)Nuclear spins are within molecules©Dr. Kay Sandberg_________4.7 T requires 200 MHz for proton spin flip50.4 MHz for C-13 spin flipSpins experiencingdifferent _________ fieldswill resonate at different ___________.419Continuous-wave NMRSection 13.3Hp= Ho- Hemagnetic field“felt” by nuclear spin (effective)externalmagnetic field (applied)opposing e-induced field(local)hν = ΔEHp8 X 10-5kJ/mol4.7 T4.7 Tdepends on __________ (depends onmolecule)_______ to achieve resonance©Dr. Kay SandbergContinuous-wave NMR200 MHz20Different electron densitiesHp= Ho- HeSection 13.3Hoσ bond e-“felt”fieldappliedfieldlocalfieldLarger amount of electron density in σ bondSmaller amount of electron density in σ bond________ opposing Heproton is _____________ opposing Heproton is _________©Dr. Kay Sandberg21TMS vs CH3FSection 13.3HCSiHHTMS (tetramethylsilane)reference to which all peaks are comparedCH3CH3CH3Si is electro__________(_____ electron density in C-H bond)FluoromethaneF is very electro_________(______ electron density in C-H bond)HCFHHHCFHH©Dr. Kay Sandberg22TMS vs CH3FHp= Ho- HeSection 13.3Ho“felt”fieldappliedfieldlocalfieldWhich diagram above would correspondto fluoromethane’s local field? ©Dr. Kay Sandberg23TMS vs CH3FHp= Ho- HeHp= Ho- HeSection 13.4Hp= Ho- HeHoHp= Ho- He4.7 T4.7 T______opposingfield_______opposingfield______ field_____ field©Dr. Kay Sandberg24Shielded vs deshieldedHp= Ho- HeHoHp= Ho- He________protonlower field


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