Material Purity in Calculations

In order to provide common grounds for experiment comparisons, Espresso ELN adheres to textbook stoichiometric calculations in which the material purities always are part of the calculations. Therefore the calculated yield of a reaction depends on the purities of starting material and product; equivalents calculations do take into account reagent and starting material purities.


Reference Starting Material(s) & Product(s)

The reference starting material (aka limiting reagent) is defined as the leftmost starting material in the reaction sketch, if several are present. It is the reference base for equivalent and yield calculations. If added in several portions, the total sum of it is calculation relevant. The reference product (aka limiting product) is defined as the leftmost product in the reaction sketch, if several products are present. If isolated in several batches, their sum is used for the determination of the overall reaction yield.

Additional Equivalent Units

In addition to the standard weight, volume and equivalent units, Espresso ELN introduces some additional stoichiometric units, which originate from common use in experiment planning:

  Reagents:

  • Milli-equivalents (mq):  1 mq = 0.001 equivalent of reagent. This unit is essential for catalytic processes, in which the catalyst is added in very small amounts.

  Solvents:

  • Volume equivalents (vq): Milliliters of solvent per gram crude reference starting material.
  • Volume equivalents (mv): Milliliters of solvent per mmol reference starting material.
  • Absolute volume equivalents (av): Milliliters of solvent per purity corrected gram of reference starting material. 

  Auxiliaries:

  • Weight equivalents (wq): Grams of auxiliary (charcoal, silicagel, etc) per gram crude reference starting material.
  • Absolute weight equivalents (aw): Grams of auxiliary per purity corrected gram of reference starting material. 


Special Stoichiometry

There may be situations where a reactant splits into several equal product parts (e.g. after the monomerization of a trimer), or when several parts of the reactant are merged to a single product (e.g. the formation of acetic anhydride from acetic acid). Drawing the reaction sketch here as usual, i.e. one reactant leading to one product, normally would result in an incorrect formal stoichiometry and an associated incorrect yield. However, applying the stoichiometric corrections provided in the products panel allows drawing the reaction sketch as usual, i.e. one reactant and one product, while still obtaining the correct yield.


Calculation Precision

Espresso ELN displays material amounts in 3 digits precision (rounded), all internal calculations occurring in 7 digits precision. The goal is to display material amounts in a precision actually achievable when weighing in a material in the lab. Thus, e.g. displaying a solvent volume in 7 digits precision certainly is of little practical value. 3 digits were chosen as a reasonable precision, being well achievable in the lab, and resulting in max. 0.5% rounding error (average 0.1%).