Molecular weight
To a first approximation the molar extinction
coefficient (e) of a chromophore (absorbing molecular
group) is unaffected by distant substituent groups
in a molecule. Therefore, if e of the chromophore is
known from another related compound in the series,
the molecular weight of the new derivative can be
calculated from the absorbance of a solution of
known concentration, as mol. wt. = 10 elE.