C8953 NMR structural analysis - seminar Basic concepts & Vector model Jan Novotný novotnyjan@mail.muni.cz March 14, 2018 Assign correct value of chemical shift to labelled NMR active atoms1 : 1 http://www.chem.wisc.edu/areas/reich/chem605/ Assign correct value of chemical shift to labelled NMR active atoms1 : 1 http://www.chem.wisc.edu/areas/reich/chem605/ Diastereotopicity1 1 http://www.chem.wisc.edu/areas/reich/chem605/ Diastereotopicity1 1 http://www.chem.wisc.edu/areas/reich/chem605/ Determination of regioisomers 300MHz 1 H NMR spectrainCDCl3 OH CH3 CH3 2,4-methylphenol OH CH3 CH3 2,5-dimethylphenol OH CH3CH3 2,6-dimethylphenol OH CH3 CH3 2,3-methylphenol OH CH3 3,4-dimethylphenol OH CH3CH3 3,5-dimethylphenol CH3 H3 H4 H6 H3 H4 H5 H2H6 H5 H2H6 H4 H6 H5 H3 H4 H5 H6 8 7 6 5 4 3 2 1 0 5X expansion 8 7 6 5 4 3 2 1 0 5X expansion This work by Dr. James S. Nowick, Professor of Chemistry, University of California, Irvine, is licensed under a Creative Commons Attribution 4.0 International License. Spectra are from Sigma-Aldrich (www.sigmaaldrich.com) under fair use. 8 7 6 5 4 3 2 1 0 5X expansion 8 7 6 5 4 3 2 1 0 5X expansion 5X expansion 8 7 6 5 4 3 2 1 0 Determination of regioisomers OH CH3CH3 H2H6 H4 4 300MHz 1 H NMR spectrainCDCl3 OH CH3 CH3 2,4-methylphenol OH CH3 CH3 2,5-dimethylphenol 2,6-dimethylphenol OH CH3 CH3 2,3-methylphenol OH CH3 3,4-dimethylphenol OH CH3CH3 3 H3 H4 H6 OH CH3CH3 H3 H4 H5 H2H6 H5 H2H6 H4 H6 H5 H3 H4 H5 H6 8 7 6 5 4 3 2 1 0 5X expansion 8 7 6 5 4 3 2 1 0 5X expansion This work by Dr. James S. Nowick, Professor of Chemistry, University of California, Irvine, is licensed under a Creative Commons Attribution 4.0 International License. Spectra are from Sigma-Aldrich (www.sigmaaldrich.com) under fair use. 8 7 6 5 4 3 2 1 0 5X expansion 8 7 6 5 4 3 2 1 0 5X expansion 5X expansion 8 7 6 5 4 3 2 1 0 OH CH3 CH3 H4 H5 H6 645 1 OH CH3CH3 H3 H4 H5 4 3,5 1 2,6 1 OH CH3 3 H2H6 H5 625 OH CH3 CH3 H3 H4 H6 3 4 6 1 1 Draw the estimate of 13 C NMR spectrum (with and without 1 H decoupling) and APT experiment: Draw the estimate of 13 C NMR spectrum (with and without 1 H decoupling) and APT experiment: Analysis of simple pulse sequences using vector model simple model based on rotation of the vector of bulk magnetization in the plane perpendicular to the vector of magnetic field, direction is determined by the "right-hand rule" NMR signal is detectable only as coherent magnetization oscillating in xy plane the free precession ω (due to the B0) of magnetization vector is eliminated by introducing rotating frame ω0 ⇒ magnetic field of excitation pulses (B1) is motionless and the individual resonance frequencies differs in so called offset Ωi = ωi − ω0 applicability of vector model is rather limited to simple single-quantum experiments without transfer of polarisation x y z B0 Bpulse T1 relaxation Apply following sequence (inversion recovery) to isolated spin characterized by a) τ = 2 ∗ T1 and b) τ = 0.2 ∗ T1. Draw semi-quantitatively resulting spectrum. τ 180x 90y- T1 relaxation Apply following sequence (inversion recovery) to isolated spin characterized by a) τ = 2 ∗ T1 and b) τ = 0.2 ∗ T1. Draw semi-quantitatively resulting spectrum. τ 180x 90y- x y z x y z x y z x y z x y z x y z +0.73M0 -0.65M0 1-1 sequence Draw the evolution of macroscopic magnetization through the sequence: 90(y) - τ - 90(y) - aq Consider the evolution of an isolated spin due to the chemical shift. 1. How does the result differ for the following offsets: Ωτ = 0, π/2, π. 2. Draw lineshapes of resulting signal assuming the a) y+ b) x+ corresponds to zero phase of receiver. τ 90y 90y 1-1 sequence Draw the evolution of macroscopic magnetization through the sequence: 90(y) - τ - 90(y) - aq Consider the evolution of an isolated spin due to the chemical shift. 1. How does the result differ for the following offsets: Ωτ = 0, π/2, π. 2. Draw lineshapes of resulting signal assuming the a) y+ b) x+ corresponds to zero phase of receiver. τ 90y 90y x y z x y z x y z 0 π/2 π x y z 0 π/2 π ω ω y+ x+ Heteronuclear spin echo By using vector diagrams determine the result of attached pulse sequence. 1. Ignore 180 pulse in hydrogen channel for isolated spin systems a) 13C-1H and b) 13C-1H2. Explain the role of CPD block. 2. Lets consider the complete sequence and isolated spin systems a) 13C-1H and b) 13C-1H2. τ=1/2J 90y 180x 13 C τ=1/2J 180x 1 H CPD Heteronuclear spin echo By using vector diagrams determine the result of attached pulse sequence. 1. Ignore 180 pulse in hydrogen channel for isolated spin systems a) 13C-1H and b) 13C-1H2. Explain the role of CPD block. τ=1/2J 90y 180x 13 C τ=1/2J 1 H CPD x y z x y z x y z CH...J=JHC CH2...J=2*JHC CHα CHβ y +Ωτ x y z y +Mx +Mx +πJτ -πJτ CHαCHβ CHβ CHα +Ωτ CH2αα CH2αα CH2αα CH2ββ CH2ββ CH2ββ Heteronuclear spin echo By using vector diagrams determine the result of attached pulse sequence. 2. Lets consider the complete sequence and isolated spin systems a) 13C-1H and b) 13C-1H2. τ=1/2J 90y 180x 13 C τ=1/2J 1 H CPD x y z CH...J=JHC CH2...J=2*JHC y x y z y 180x y y -Mx +Mx CH2ββCH2αα CH2αα CH2αα CH2αα CH2ββ CH2ββ CH2ββ CHβ CHβ CHβ CHβ CHα CHα CHα CHα Next topic 2D NMR - homonuclear experiments