As more information is needed to solve an unknown, it becomes useful to understand what information is available, make a hypothesis and then get to the grunt work of eliminating the unlikely candidates.
Below is a summary explaining some of the information that can be extracted from the problem set.
- Given an unknown compound as organic, the focus is best kept with the elements C, H, N and O.
- The ESI(neg.)-ToF spectrum indicates a singly-charged ion at m/z 692.137. If we presume this is the [M-H]- ion with a tolerance of 1 mDa, then we can limit the number of possible molecular formula(e) (MF). See the table below.
- The MS isotope pattern excludes atoms such as Cl, Br and S.
- The upper range for the C atoms is 57 (≈693/12).
- The 13C / 12C ratio indicates the C atom count at closer to 36 (≈40/100*100/1.1).
- The 13C NMR data indicates at least 12 C atoms.
- The carbons at 70, 167 and 169 ppm indicate at least 3 O atoms.
- The height difference for the C atoms at 43 and 47 ppm in respect to the other signals indicates a potential dimer or trimer or more. Multiples for the total C atoms are: 10C+2C, 20C+2C, 30C+2C, etc.
Multiples for the protonated C/H atoms are: 5 CH: 1 CH2: 1 NH = 6C/8H, 10 CH: 2 CH2: 2 NH = 12C/16H, 15 CH: 3 CH2: 3 NH = 18C/24H. The OH groups are not indicated.
Table of Potential Molecular Formulae
# MF Calc. Mass Mass Diff. RDBE (N(III);N(V))
1 C32H27N3O15 ___692.137 0.000 21.0;24.0
2 C31H21N10O10 __692.137 0.000 26.5;36.5
3 C30H15N17O5 ___692.137 0.000 32.0;49.0
4 C17H23N15O16 __692.138 0.000 14.0;29.0
5 C46H15N9 ______692.138 -0.001 44.0;53.0
6 C47H21N2O5 ___692.138 -0.001 38.5;40.5
7 C32H17N14O6 __692.138 -0.001 31.5;45.5
8 C33H23N7O11 __692.138 -0.001 26.0;33.0
The remaining MF C32H27N3O15 is the best fit for the unknown compound.