Draw the two rotamers of the ylide and calculate the percent composition of each
ID: 509235 • Letter: D
Question
Draw the two rotamers of the ylide and calculate the percent composition of each rotamer in the (CD3)2SO 1H NMR spectrum. (Note that you will not be able to determine which rotamer corresponds to each set of peaks). Calculate the 1H–
31P coupling constant for the ylide in (CD3)2SO. Be sure to show your work!! Thanks!! The reaction is a Wittig reaction between methyl(triphenylphosphoranylidene)acetate and 2-nitrobenzaldehyde. No empirical formula was given-- this is all the info i have!
'HNMR of 2-nitrobenzaldehyde in CDC, 300 MHz Spectrometer 8.2 8.1 8.0 79 7.8 77 76 fl (ppm) 9.5 10.5 100 9.0 fl (ppm) 8.0 CHCs 7.0Explanation / Answer
Wittig reaction is defined as the production of majoly E- alkene, from the Methyl( triphenylphosphphoranylidiene)acetate. act as ylide and the 2-nitrobenzaldehyde. where ylide is the formation when acedic hydrogen is removed from the the triphenylphosphine group in the influence of aldehydic group.
(Ph)NO2-CH=O + (Ph)3P-CHCOOCH3----------.> (Ph)NO2-CH=CH-COOCH3 + (Ph)NO2-CH=CH-COOCH3
Trans (Major ) CIS
that highlighted portion means it is above the plane.
Therefore the Two ROTAMERS ARE SHOWN ABOVE.
Rotamers are conformational isomers (Ph)3P=CHCOOCH3 AND (Ph3)P-COOCH3
Percentage composition for this is as follows:
2.533/ (2.478+2.533)
= 2.533/5.011
= 0.505* 100
=50.5%
and same as for another rotamers .
coupling constant: It is the distance between the two peaks .
which denoted as J
FROM the 13P NMR data
frequency in PPM= 17.27
Frequency (HZ) = PPM * carrier frequency /10^-3
= 17.27 * 0.1727/10^-3
= 2,970.44 Hz
In this peak the distance is 1.1 PPM between the multiplet .
and the and 1.1 FOR OTHER SINGLE PEAK.
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