See also Entering Formulas.

Element Subtraction was added to allow one to quickly find the mass or empirical formula of a compound that has lost one or more elements due to a reaction or a neutral loss in mass spectrometry. For example:

C_{6}H_{5}Cl>HCl means C_{6}H_{5}Cl minus HCl, having a mass of 76.0959 Da (average mass), equivalent to C_{6}H_{4}

The elements to the right of the > symbol must all be present in the elements to the left of the > symbol, otherwise an error will occur. Furthermore, the number of atoms of a given element listed to the right of the > symbol cannot be greater than the number of atoms of the element to the left of the > symbol. Thus, the following formulas will result in an error:

C_{6}H_{5}Cl>HBr | since Br is not present in C_{6}H_{5}Cl |

C_{6}H_{5}Cl>HCl_{2} | since only one Cl atom is present in C_{6}H_{5}Cl |

If you include multiple > symbols in a formula, then the order of operation is right-to-left. For example:

C_{6}H_{5}Cl_{3}>H_{3}Cl_{2}>HCl

will first be converted to

C_{6}H_{5}Cl_{3}>H_{2}Cl

and then to

C_{6}H_{3}Cl_{2}

The mass of C_{6}H_{3}Cl_{2} is 145.99342 Da (average mass), and consequently this is the mass returned for C_{6}H_{5}Cl_{3}>H_{3}Cl_{2}>HCl

If you choose Convert To Empirical Formula, then the empirical formula returned is C_{6}H_{3}Cl_{2}

Abbreviations may contain formulas having > symbols in them. Thus, if the abbreviation J is defined to be C_{6}H_{5}Cl>HCl (mass 76.0959 Da), then the formula H_{2}J will have a mass of 78.11184 Da. If you choose Expand Abbreviations for the formula H_{2}J, then the formula will be replaced with H_{2}C_{6}H_{5}Cl>HCl. However, if the original formula is J_{2} and you choose Expand Abbreviations, then we cannot simply replace J_{2} with (C_{6}H_{5}Cl>HCl)_{2} since that is an invalid formula. Consequently, J is first converted to its empirical formula, giving (C_{6}H_{4})_{2} This same situation applies if J is in the middle of a formula. For example, H_{2}JO_{2} will be converted to H_{2}C_{6}H_{4}O_{2} when choosing Expand Abbreviations, or to C_{6}H_{6}O_{2} when choosing Convert to Empirical Formula.

Back to the Molecular Weight Calculator download page