Question

Help me find this Aldose Unknown based on its HNMR, CNMR, and optical rotation.

This unknown was very dark in color and it was optically active. The five options are listed below:

22._ 170. 0 160.0 150.0 40.0 130.0 120.0 110.0 100. 0 90.0 80.0 700 60.0 50.0 40.0 30.0 20.0 A A A 70.650 7170 507 170.135 169878 909 77.299 77.041 76.799 68352 6R ONS 62038 61.70 20 794 20 600 20:59 per Million

Answer 1

1) The H NMR spectrum shows total 11 peaks ( 11 types of protons). Except thp Peak at 4.7 ppm that is a solvent peak, may be for CD3OD. Integration on peaks shows that, total no. of 11 types of Protons = 22.

2) The 13C NMR data shows total 12 peaks. (Except 77.2 that is for slovent CDCl3).

3) Physical properties shows, it is dark in colour.

From the above point 2: 12 peaksin 13C nmr (12/2 = 6), means 6 types of Carbon are there so, we can interprete that data is +- mixture of Aldohexose and not for Aldopentose, so out of 5 options 2 of Xylose and arobose is eliminated.

Now, from the remaining hexose Glucose, mannose & galactose only, Mannose has 11 different types of protons, and HNMR shows 22 types of protons for +- or DL mixture of mannose.

Moreover, mannose is brown in colour.