670 likes | 1.63k Views
NMR N uclear M agnetic R esonance. Heteronuclear NMR:. Index. NMR-basics. H-NMR. NMR-Symmetry. Heteronuclear-NMR. Proton with Carbon-13 coupling. Proton with Fluorine-19 coupling. Fluorine-19: Fluoroacetone. Phosphorus-31. Phosphorus-31: Coupling with 1 H.
E N D
NMRNuclear Magnetic Resonance HeteronuclearNMR: Index NMR-basics H-NMR NMR-Symmetry Heteronuclear-NMR
AQ: P31 AQ: P31 Phosphorus-31 28 Hz 8Hz dt H1 decoupling
AQ: P31 39 Hz Phosphorus-31 9 Hz H1 decoupling NMR – From Spectra to Structures An Experimental approachSecond edition (2007) Springler-Verlag Terence N. Mitchellm Burkhard Costisella
N15 NMR 10 mm tube 25% in CDCl3 Inverse gated D1=15 s Total time 12 hrs NMR – From Spectra to Structures An Experimental approachSecond edition (2007) Springler-Verlag Terence N. Mitchellm Burkhard Costisella
C-13 NMR: Quantitative?? • In C-13, some carbons can have long relaxation time: If the relaxation delay is not long enough, the long relaxation carbons will not achieve full amplitude • NOEs varies for the various carbons • Number of data points used to record the data might not be sufficient • The efficiency of the pulse vary depending if a signal is in the center of the window or on the side.
NMR – From Spectra to Structures An Experimental approachSecond edition (2007) Springler-Verlag Terence N. Mitchellm Burkhard Costisella AQ: C13 Normal C13 measure time 1.5 hrsNOE present, no integration possible 2 C2 3 1 H1 decoupling 3JCP = 2.3 3JCP = 5.5 2JCP = 7.2 1JCP = 201.3 C3 PCHO2 C1 1JCP OCH2 CH3
NMR – From Spectra to Structures An Experimental approachSecond edition (2007) Springler-Verlag Terence N. Mitchellm Burkhard Costisella AQ: C13 AQ: C13 C13-NMR 2 d 1 3 C13, H-coupled H1 decoupling dd t q C2 PCHO2 C3 1JCP C1 OCH2 CH3
NMR – From Spectra to Structures An Experimental approachSecond edition (2007) Springler-Verlag Terence N. Mitchellm Burkhard Costisella C13 coupling to proton 2 1 3 3JC3-H2 = 7.9 2JC3-H2’ = 5.4 C3-Cl
AQ: C13 AQ: C13 AQ: C13 C13 extracting J values Me 3JPC = 5.5 Hz H1 decoupling CH2selective dec. Quartet : CH3 split by P (doublet) Split by CH2 triplet 1JCH = 127.7 Hz
NMR – From Spectra to Structures An Experimental approachSecond edition (2007) Springler-Verlag Terence N. Mitchellm Burkhard Costisella AQ: C13 C13 inverse gated: integrationMeasuring time: 28 hoursD1=120 s H1 decoupling D1 off
Multiplicity detection DEPT : CH, CH3 CH2 APT : CH, CH3 C , CH2 Normal C13
Carbon-13 Shift Acid Amide Ester Ketone Aldehyde O C = O C – O C – O = C = C C C – C C=C 200 150 100 50 0
Alkanes d = -2.5 + SnA 1 2 3 4 5 CH3-CH2-CH-CH2-CH3 6 CH3 dC1 = -2.5 + 1a + 1b + 2g + 1d dC1 = -2.5 + 9.1 + 9.4 + 2(-2.5) + .3 = 11.3 dC2 = -2.5 + 2a + 2b + 1g + 2o(3o) (Secondary carbon bound to tertiary) dC2 = -2.5 + 18.2 + 18.8 + (-2.5) + (-2.5) = 29.5 dC3 = -2.5 + 3a + 2b + 2{3o(2o)} dC3 = -2.5 + 27.3 + 18.8 + (-7.4) = 36.2 dC6 = -2.5 + 1a + 2b + 2g + 1o(3o) = 19.3
Alkanes dC1 = -2.5 + 1a + 1b + 2g + 1d = 11.3 dC2 = -2.5 + 2a + 2b + 1g + 2o(3o) = 29.5 dC3 = -2.5 + 3a + 2b + 2{3o(2o)} = 36.2 dC6 = -2.5 + 1a + 2b + 2g + 1o(3o) = 19.3 C2 C1 C3 C6 2 3 1 6
Substituted Alkanes CH3-CH2-CH2-CH2-CH3 13.9 – 22.8 – 34.7 g b a CH3-CH2-CH-CH2-CH3 OH CH = 34.7 + 41 = 75.7 ppm CH2 = 22.8 + 8 = 30.0 ppm CH3 = 13.9 + (-5) = 8.9 ppm
CH = 34.7 + 41 = 75.7 ppm g b a CH3-CH2-CH-CH2-CH3 CH2 = 22.8 + 8 = 30.0 ppm OH CH3 = 13.9 + (-5) = 8.9 ppm
Shift Calculation: • Select a suitable model • Use proper substituent effects to predict the shifts of the various carbonsThis gives a crude estimate without taking into account the geometry • For cyclohexanes, substituents effects are compiled in terms of axial/equatorial orientation
d- d+ CH2 CH OMe CH2 CH OMe 84.2 153.2 CH2 CH2 C C C d- d+ OEt CH C CH OEt C Unsaturated compounds: Electronic Effects Alkenes d- 129.3 d+ 157 Allenes 75-97 200-215 Alkynes 65-90 ppm 23.2 89.4
Example: Benzene Calculation => distinguish isomers Experimental shifts 152.5, 136.6, 131.7, 126.3, 121.9, 116.3 Subst. C1 ortho meta para Me 9.2 0.7 -0.1 -3.0 CH(Me)2 20.2 -2.2 -0.3 -2.8 OH 26.9 -12.8 1.4 -7.4 C1 = 128 + 9.2 – 2.8 +1.4 = 135.8 C2 = 128 + .7 - 0.3 –7.4 = 121.0 C3 = 128 – 0.1 – 2.2 + 1.4 = 127.1 C4 = 128 – 3.0 + 20.2 – 12.8 = 132.4 C5 = 128 – 0.1 – 2.2 + 26.9 = 152.6 C6 = 128 + 0.7 – 0.3 – 12.8 = 115.6 C1 = 128 + 9.2 – 2.8 – 12.8 = 121.6 C2 = 128 + .7 - 0.3 + 1.4 = 129.8 C3 = 128 – 0.1 – 2.2 - 7.4 = 118.3 C4 = 128 – 3.0 + 20.2 + 1.4 = 146.6 C5 = 128 – 0.1 – 2.2 - 12.8 = 112.9 C6 = 128 + 0.7 – 0.3 + 26.9 = 155.3
C1 = 128 + 9.2 – 2.8 +1.4 = 135.8 C2 = 128 + .7 - 0.3 –7.4 = 121.0 C3 = 128 – 0.1 – 2.2 + 1.4 = 127.1 C4 = 128 – 3.0 + 20.2 – 12.8 = 132.4 C5 = 128 – 0.1 – 2.2 + 26.9 = 152.6 C6 = 128 + 0.7 – 0.3 – 12.8 = 115.6 C2 C6 C3 C5 C1 C4
C1 = 128 + 9.2 – 2.8 – 12.8 = 121.6 C2 = 128 + .7 - 0.3 + 1.4 = 129.8 C3 = 128 – 0.1 – 2.2 - 7.4 = 118.3 C4 = 128 – 3.0 + 20.2 + 1.4 = 146.6 C5 = 128 – 0.1 – 2.2 - 12.8 = 112.9 C6 = 128 + 0.7 – 0.3 + 26.9 = 155.3 C3 C2 C5 C6 C4 C1
CarbonylsC=O Acid Ester
CarbonylsC=OEsters, Acid chlorides, Anhydrides, Amides, Carbamates
Coupling between 1H and 13C1JCH One bond coupling is proportional to % s charactersp3 : ~125 Hzsp2: ~ 165 Hzsp : ~ 250 Hz Electronegative subst. Increase JCH-OR => J ~ 140 HzCH-Cl => J ~ 150 Hz
Coupling between 1H and 13C sp3: 1JCH Increase of coupling values with the electronegativity of the substituant : CHZ Z : Li1JCH = 98 Hz Z : C1JCH = 125-129 Hz Z : NR1JCH = 131-134 Hz Z : S1JCH = 138 Hz Z : OR1JCH = 140 Hz Z : Cl1JCH = 150 Hz Z : (OR)21JCH = 162 Hz Z : Cl2 1JCH = 178 Hz 1JCH = 161 Hz 1JCH = 180 Hz 1JCH = 134 Hz 1JCH = 137 Hz 1JCH = 150 Hz
Coupling between 1H and 13C sp2: 1JCH Increase of coupling values with the electronegativity of the substituant : =CHZ =C-H 1JCH = 157 Hz 1JCH = 238 Hz 1JCH = 172 Hz 1JCH = 250 Hz 1JCH = ~200 Hz 1JCH = 182 Hz 1JCH = 202 Hz
Use of 1JCH Extremely useful for molecules where 1JCHlarger than usual Diagnostic for alkynes (250 Hz) , epoxides (180 Hz) , hemiacetal (162 Hz) and cyclopropane (161 Hz)
Coupling between 13C and 13C : 1JCC Measurable only on enriched compound Useful for setting up pulse sequences like INADEQUATE sp3 R-CH2-CH31JCC = 35 Hz 1JCC = 48 Hz sp2 1JCC = 44 Hz 1JCC = 56 Hz 1JCC = 54 Hz 1JCC = 74 Hz 1JCC = 74 Hz 1JCC = 123 Hz
Coupling between 1H and 13C2JCH Usually small and difficult to predict Typical values: -8 to +4 Hz