How do the chemical shifts and J values of the peaks in a H NMR spectrum of 5-io
ID: 558485 • Letter: H
Question
How do the chemical shifts and J values of the peaks in a H NMR spectrum of 5-iodovanillin support that specific structure rather than 6- or 2-iodovanillin?
How would an NMR spectrum look different for 6-iodovanillin or 2-iodovanillin?
Aawn EL-11 STANDARD 1H OBSERVE Autonation directory:nmr/asm/autodir File 6603 Pulse Sequence: s2pul User: Samp le: 66 zzzusr Date: So1vent: COC13 File Starting Time: 21:05:2 Completion Time: 21:12:1 Total acq. tie 1 minute UNITYplus-300 "vi300" Ambient temperature oct. 30, 2017 6602 PULSE SEQUENCE Relax delay 1.500 sec Pulse 45.0 degrees Acq time 2.000 sec Width 6003.3 H2 6 repetitions DATA PROCESSING FT size 65536 OBSERVE H1, 300.168339MHz Line broadening 0.1 Hz 10 8 ppm 11.96 12.16 11.15 0.43 1.92Explanation / Answer
NMR analysis of iodovanillin
The above shown spectrum does not have a doublet in the aromatic region for the two protons. therefore, 2-iodovanillin which has aromatic protons next to each other is not present.
The NMR of 6-iodovanillin would show symmetric structure as the ring is having two protons para to each other. These will thus not couple and would show two singlets in aromatic region of spectrum. This is not seen here adn thus 6-iodovanillin is absent.
The NMR shows aromatic protons meta to each other and couple to give the signals as shown above in the aromatic region. The proton next to -OCH3 is upfeld at 6.63 ppm. the other aromatic proton shifts downfield as it is between an aldehydic group and electronegative Iodo. Thus 5-iodovanillin is present in this case.
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