NMR assignment of an unknown
Transcription
NMR assignment of an unknown
NMR assignment of an unknown By Roy Hoffman NMR assignment of an unknown by Roy Hoffman 1 Number of protons from integrals 16 Protons: 2x3, 4x2, 2x1 ppm 5.0 4.5 4.0 3.5 3.0 2.5 NMR assignment of an unknown by Roy Hoffman 2.0 1.5 1.0 2 Number of carbon types 11 carbon types C11+H16O?, N?, etc. ppm 160 140 120 100 80 NMR assignment of an unknown by Roy Hoffman 60 40 20 3 Functionality from 1H chemical shifts 2x1vinyl CH 1x3 methyl alkyl 4x2 CH2 Aromatic ppm 9 8 CH, CH2 Me-alk Me-vinyl Vinyl CH2 Vinyl CH CH2OH 7 6 5 4 NMR assignment of an unknown by Roy Hoffman 3 2 1 4 Functionality from 13C chemical 2x1vinyl CH shifts 1x3 methyl alkyl 4x2 CH2 2x1 vinyl C 1 C=O (not CO2H because no acidic H) C11H16O C=O, CO2H ppm 175 CH, CH2 Vinyl C Vinyl CH2 CHOH, Aromatic CH2OH Vinyl CH Me 150 125 100 75 NMR assignment of an unknown by Roy Hoffman 50 25 0 5 Connectivity from 2nd order coupling – the roofing effect Roofing effect means that J=18Hz these two means trans multiplets are coupled No roofing Roofing effect effect on the means that these two other two multiplets multiplets are coupled ppm ppm 5.40 5.35 5.30 5.25 2.9 2.8 2.7 2.6 2.5 2.4 2.3 2.2 5.20 NMR assignment of an unknown by Roy Hoffman 6 The situation so far • • • • • C11H16O with C=O and 2 double bonds. This requires one ring (Without it would be C11H18O). There are 2 terminal methyls. One of the vinyls has two trans H’s Look for the following ring structures NMR assignment of an unknown by Roy Hoffman 7 Ring structures in the exercise • • • • Look for the following ring structures They may be unsaturated They may be fused There may not be any rings cyclopentane cyclohexane norborane NMR assignment of an unknown by Roy Hoffman 8 Overlapping multiplets • If the overlap is slight then it is still easy to interpret. ppm 2.24 2.22 2.20 2.18 2.16 NMR assignment of an unknown by Roy Hoffman 2.14 9 Overlapping of similar structures suggests almost identical chemical environments. These are Similar but no roofing means they are well separated Vinyl protons ppm 5.45 5.40 5.35 5.30 5.25 5.20 5.15 5.10 NMR assignment of an unknown by Roy Hoffman 5.05 10 More complex structures require 2D interpretation. •4 pairs of protons strongly coupled to each other & displays 2nd order splitting ppm 2.15 2.10 2.05 NMR assignment of an unknown by Roy Hoffman 2.00 1.95 11 COSY Two networks: CH3CH2CH=CHCH2 1 2 and C=O 3 Strong signals are 2 & 3 bond, weak signals are 4 bond 4 5 ppm ppm 5 4 3 NMR assignment of an unknown by Roy Hoffman 2 1 12 NOESY 1H Correlation between the two networks NMR is assigned Me7 9 4 5 82 3 1 1 2 3 A ring is required so close with C=O 4 O 3 10 5 1 9 6 4 2 8 7 5 ppm NMR assignment of an unknown by Roy Hoffman ppm 5 4 3 2 1 13 HSQC 4 3 Me7 9 5 8 2 1 Me75 12 89 20 40 Assign carbons attached to protons 60 80 100 120 4 3 ppm ppm 5 4 3 NMR assignment of an unknown by Roy Hoffman 2 1 14 HSQC to separate & correlate 1H signals 25 Use NOESY artifacts to determine proton connectivity 30 35 40 ppm ppm 2.1 NMR assignment of an unknown by Roy Hoffman 2.0 15 HMBC to assign other carbons Me7 9 5 8 2 4 3 •3-bond correlations strongest 1 25 1-bond correlation 50 75 O 100 3 10 5 1 9 6 4 2 6 8 7 125 150 7 10 175 ppm ppm 5 4 3 NMR assignment of an unknown by Roy Hoffman 2 1 16 Use correlation table H1 C1 O 3 10 5 1 9 6 4 2 8 7 2 C3 3 C5 H3 H4 H5 Me7 H8 3 3 H9 2 C2 C4 H2 3 2 3 3 2 3 C6 2 C7 3 3 Me7 C8 3 C9 2 2 C10 3 NMR assignment of an unknown by Roy Hoffman 4 3 17