Formula Finder
The Fragment Finder provides a list of possible formulas for a given fragment mass. However, many possible formulas are given. The isotopic peak ratios can then be used to narrow the possibilities for the formula. This "Formula Finder" application takes a different approach. From the input parent peak and fragment masses all possible formulas are generated and formulas for the parent peak that are inconsistent with the fragment formulas are dropped. For example, a fragment may only have formulas with one or more nitrogens, therefore the parent formula must have at least one nitrogen also. For small molecules this procedure decreases the number of possible formulas by 20-30%, so you'll still get a list of 20-30 formulas.

To narrow the possibilities further, there are several options that limit the possible formulas:

The maximum number of double bonds and rings and the electron parity (odd/even) are not used in the screening logic. The maximum and parity are just used as a final filter before the formulas are printed. Your parent peak mass is also tested for bad and unlikely losses. If no formulas are printed, then the input parent peak is also unlikely to be the molecular ion.
Enter the parent peak mass:
Enter the fragment masses:
Maximum number of double bonds and rings:
Maximum number of nitrogens:
List odd-electron molecular ions only:
Odd electron fragments must correspond to the loss of a stable neutral molecule from an odd electron ion


e/o = even/odd electrons
dbr = double bonds and rings

If the trial formula is CcHhOoNn then the number of double bonds and rings is (2c-h+n+2)/2.

Colby College Chemistry, 1998
funding provided by a grant from NECUSE (New England Consortium for Undergraduate Science Education)