code: public Double calculateMolecularWeight(String notation) throws MonomerLoadingException, BuilderMoleculeException,
  			CTKException, ValidationException, ChemistryException {
  		Double result = MoleculePropertyCalculator.getMolecularWeight(validate(notation));
  		setMonomerFactoryToDefault(notation);
  		return result;
  	}
docs: method to calculate from a non-ambiguous HELM input the molecular weight
  
  @param notation
  HELM input
  @return moleuclar weight from the HELM input
  @throws MonomerLoadingException
  if the MonomerFactory can not be refreshed
  @throws ValidationException
  if the HELM input is not valid
  @throws BuilderMoleculeException
  if the molecule for the calculation can not be built
  @throws CTKException
  general ChemToolKit exception passed to HELMToolKit
  @throws ChemistryException
  if the Chemistry Engine can not be initialized