Hai Truong 's Analysis of the H-NMR of (2S,3R)-2-amino-3-methyl-pentanoic acid



(2S,3R)-2-amino-3-methyl-pentanoic acid

This is the H MNR spectrum of (2S,3R)-2-amino-3-methyl-pentanoic acid:


Here is the analysis that shows what we expect to see in H MNR strectrum of this acid:


Analysis_01.jpg



Hmnr_CH3.jpg
This figure shows the region from 0.9-0.97ppm which will correspond H of akane in -CH3 (red group, 0.9-1.5ppm, lit.). There are 3 peaks but actually is doublet of double because red group is next to 2 slightly different hydrogens of -CH2-. There are actually 4 peaks, but 2 peaks in the middle are so close that they make one large single peak.

Hmnr_CH2.jpg
This figure shows the region of 2 peaks in 0.976--1.024 ppm. These 2 peaks corresponds to 3Hs of alkane group -CH3 (blue group). There is 2 peaks (doublet) because these 3Hs are only next to one H of adjacent carbon (green hydrogen).



Hmnr_OH.jpg
This figure shows only one peak at 4.82 ppm. This peak correspond to H of -OH (black H) (4.5ppm, theoretically). There is only one peak because it is not close to any H.
[No the 4.8 ppm peak is HDO created by the exchange of the NH2 and COOH hydrogens with the solvent D2O JCB] -ok So, 4.8ppm peak is caused by the exchange of NH2 and COOH, thanks professor.




Hmnr_NH2.jpg

This figure shows 2 peaks at 3.654-3.600ppm which correspond to Hs in yellow circle. It have high ppm because H is deshielded by next C=O group and NH2 group. There are 2 peaks (doublet) because it interacts with H in green circle.

Hmnr_CH2_8_peaks.jpg
This figure contains multipeaks about 16 peaks in region of 1.180 -1.320ppm which correspond to the first H of alkane -CH2- (purple circle ). Because these 2Hs connect to carbon next to chiral carbon, they are slightly different. These multipeaks is quartet (3Hs from red circle) of doublet (H in green circle) of doublet (of H in the same carbon).



Hmnr_CH_24_peaks.jpg
This region comprises of multipeaks about 32 peaks (quartet of doublet of doublet of doublet) of green H. This green hydrogen is actually interact with totally 3 different adjacent Hs and one group of 3Hs: green(3Hs), yellow (1H), and purple(2 different Hs next to chiral C). In addition, because this H is of alkane group, so it is still in the region of 0.9-1.5ppm theoretically, but it is little more deshielded by -NH2 group, then located in higher region 1.9-2.030ppm.


Hmnr_H2N-CH_6_peaks.jpg
This figure contains multipeaks about 16 peaks in region of 1.380 -1.540ppm which correspond to the second H of alkane -CH2- (purple circle ). Because these 2Hs connect to carbon next to chiral carbon, they are slightly different. These multipeaks is quartet (3Hs from red circle) of doublet (H in green circle) of doublet (of H in the same carbon).