Quantify how efficiently a reaction produces the desired product relative to all converted material. Choose between product-based and reactant-based selectivity — results update live as you type.
Selectivity measures how well a reaction channels converted starting material into the desired product, rather than into unwanted by-products. A highly selective reaction wastes little material on side-reactions — directly reducing raw material costs, downstream separation burden, and waste generation. It is a key companion to yield (which measures how much of the theoretical maximum is achieved) and atom economy (which assesses the theoretical efficiency of the balanced equation).
| Symbol | Term | Notes |
|---|---|---|
| \(S\) | Selectivity | %; ideal value = 100% |
| \(n_{\text{desired}}\) | Amount of desired product formed | mol (or g, if consistent throughout) |
| \(n_{\text{converted}}\) | Total amount converted | Product-based: \(n_{\text{desired}} + \Sigma\, n_{\text{by-products}}\) Reactant-based: moles of limiting reactant consumed |
All quantities must be in the same units (mol, mmol, g, etc.). Selectivity and yield are related but distinct: you can have high yield with low selectivity if you run the reaction to full conversion using excess reactant, and vice versa.
| Mode | Denominator | When to use |
|---|---|---|
| Product-based | Sum of all products identified (desired + all by-products) | When you have quantified all products but have not measured reactant consumption directly. The most common mode in organic synthesis. |
| Reactant-based | Moles of limiting reactant consumed (initial minus residual) | When conversion is measured independently (e.g. by GC of reaction mixture) and not all products have been isolated. Common in catalysis and process chemistry. |
| Metric | What it measures | Stage |
|---|---|---|
| Atom Economy (AE) | Theoretical fraction of reactant mass incorporated in desired product (from balanced equation) | Design |
| % Yield | Fraction of theoretical product actually isolated — depends on both selectivity and conversion | Experimental |
| Selectivity | Fraction of converted material that forms the desired product — independent of conversion | Experimental |
| E-factor | Total waste per unit product — captures solvents, workup waste, and by-products | Experimental |
| TON / TOF | Catalyst productivity and rate — complements selectivity in catalytic reactions | Experimental |
Choose how selectivity is calculated. Product-based uses all identified products as the denominator — ideal when you have isolated or quantified all products. Reactant-based uses moles of consumed limiting reactant — ideal when conversion is measured directly (e.g. by GC) and some products are unidentified.
All amounts entered in sections 04–06 must be in the same units selected above.
Enter the name and amount of the desired product actually formed. Use the same units as selected in section 03.
Enter each by-product or undesired product formed in the reaction. Their combined amount, plus the desired product, forms the denominator. Used in product-based mode.
| By-product name | Amount (mmol) |
|---|
Enter the limiting reactant name and the amount consumed (initial amount minus amount remaining). Used in reactant-based mode. Use the same units as section 03.
| Product / species | Type | Amount | % of converted | Visual |
|---|---|---|---|---|
| Enter product amounts above to see breakdown. | ||||
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