C8953 NMR structural analysis - seminar Symmetry, 1D 13C-NMR Jan Novotny 176003@mail.muni.cz March 2, 2022 1 H vs 13 C NMR 1 H 13 C Spin number 1 H: s=1 2 × 2 H: s=1 13 C: s=1 2 × 12 C: s=0 Abundance [%] 99.98 1.1 Gyromagnetic ratio [107 rad.T−1 .s−1 ] 26.8 6.7 Chemical shift range [ppm] 0 - 15 0 - 200 Nuclear shielding σdia σdia + σpara Integration of signals � × T1 relaxation [s] 1-20 1-40 Homonuclear J-interaction � × H↔C J-interaction (∼ 100-250 Hz) carbon satellites (n + 1) splitting × decoupling 1 H vs 13 C NMR 1 H 13 C Spin number 1 H: s=1 2 × 2 H: s=1 13 C: s=1 2 × 12 C: s=0 Abundance [%] 99.98 1.1 Gyromagnetic ratio [107 rad.T−1 .s−1 ] 26.8 6.7 Chemical shift range [ppm] 0 - 15 0 - 200 Nuclear shielding σdia σdia + σpara Integration of signals � × T1 relaxation [s] 1-20 1-40 Homonuclear J-interaction � × H↔C J-interaction (∼ 100-250 Hz) carbon satellites (n + 1) splitting × decoupling 1 H-13 Cα 1 H-13 Cβ 1 H-12 C ωC-0.51 JHCωC+0.51 JHC 1 JHC 1 JHC 1D 1 H NMR 1D 13 C NMR 1 Hβ-13 C1 Hα-13 C 1 H decoupled Important regions of 13 C chemical shifts Aldehydes RCH=O Ketones R1R2C=O Carboxylic acids R-CO2H Esters R-CO2R' Amines R-CONR2' C-NO2 C-F C-Cl C-Br C-I C-H Saturated Hydrocarbons C-NH2 C-OH C-SR C-OR C-Ar C-SO2 R C-CO R C-C=C C CR RC N Heteroaromatics Aromatics R2C=CH2 RHC=CHR R2C=CH2 200 150 100 50 0.0 ppm(δ) Alkenes Alkynes 1 JCH depends on the bond order ( hybridization ⇔ s-character ) � -C-H 1JCH ≈ 125 Hz � =C-H 1JCH ≈ 160 Hz � ≡C-H 1JCH ≈ 250 Hz � X-C-H � X = N, O, S, F, Cl, . . . 1 JCH ⇑ � X = Li, Mg, . . . 1 JCH ⇓ 2 JCH < 0 or close to zero (<3 Hz) � often not observable in 1D 13 C H-C interaction suppressed by DECOUPLING ⇒ simplification of spectra (splitting removed, sensitivity) � saturation of 1H energy levels during decoupling enhances relatively intensity of 13C signals because of heteronuclear nOe ⇒ quaternary carbons usually less intensive. Diastereotopicity1 Determine the equivalency of geminal protons 1 http://www.chem.wisc.edu/areas/reich/chem605/ Values of chemical shift of important solvents Abbr. Formula 1 H 13 C ACN CH3CN 1.9 118 Benzene C6H6 7.2 128 CHCl3 7.2 77 DCM CH2Cl2 5.3 54 DMF (CH3)2NCHO 2.9, 8.0 32, 163 DMSO (CH3)2SO 2.5 40 MeOH CH3OH 3.3, 4.8 49 Water H2O 4.8 EXPLAIN effect of solvent on the position of residual 1H water signal: CHCl3 - 1.6, ACN - 2.1, DMSO - 3.3, MeOH - 4.9 How many 13 C signal would you expect in the NMR spectrum? Ru N N N N Cl Cl Cl S CH3 CH3 O N+ - N H 1D 13 C-NMR 1, bottom without CPD 1D 13 C-NMR 2 � ZOOM of coupled region of most deshielded signals � coupled spectrum � spectrum with decoupling 1D 13 C-NMR 3, b - zoom of right region, a - full decoupled spectrum 1D 13 C-NMR 4, consider equilibrium minor-major form Which form dominates and why?