About This LogD Calculator
LogD describes how a compound distributes between an organic phase and water at a selected pH. It is useful in screening, formulation, extraction, and general research. Unlike LogP, LogD changes when a compound gains or loses charge. That makes pH and pKa important inputs. A neutral molecule usually partitions into the organic phase more easily. An ionized molecule usually stays in water more strongly.
Why LogD Matters
LogD helps compare compounds under realistic conditions. Many chemicals are weak acids, weak bases, or ampholytes. Their charge state shifts as pH changes. A single LogP value cannot show that shift. A LogD estimate gives a clearer view for buffers, samples, and test methods. It can support early ranking before full lab testing. It can also explain why one pH gives stronger extraction than another.
Calculation Approach
This tool starts with LogP and converts it into P. It then estimates the neutral fraction from pH and pKa. For weak acids, higher pH reduces the neutral fraction. For weak bases, lower pH reduces the neutral fraction. For ampholytes, both acidic and basic terms are considered together. The final D value is P multiplied by the neutral fraction and any correction factor. The calculator then returns LogD by taking the base ten logarithm.
Measured Mode
Measured mode is included for experiments. Enter the amount in the organic phase and aqueous phase. Add each phase volume. The tool converts amounts into concentrations. It then divides organic concentration by aqueous concentration. This is helpful when lab data comes from tubes, plates, or partition studies. Use the same amount unit for both phases.
Best Use Tips
Use reliable pKa and LogP values. Match the pH to your buffer. Check units before exporting results. Treat estimates as guidance, not a replacement for validated assays. For ionizable mixtures, review assumptions carefully. Small pKa errors can change LogD noticeably near the pKa point. Save CSV or PDF output when comparing several test conditions.
Keep notes about solvent, temperature, salt level, and shaking time. These factors can affect observed distribution. When results guide decisions, repeat critical measurements. Compare estimates with experimental controls. This keeps the calculator useful while maintaining scientific caution. Good records help later audits and revisions.