ORG-21

Octanol–water log P

log P = log10 (c_oct / c_w). Lipophilicity.

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Physical organiclog P

Governing equation

\log P=\log_{10}(c_{\mathrm{oct}}/c_{\mathrm{w}})

where

c_{oct}: Octanol concentration (mol/L)
c_w: Water concentration (mol/L)
\log P: log P (—)

Lecture brief

Historical brief

Hammett (1937) and Taft linear free-energy, E-factor green metrics, Woodward–Fieser UV and Claisen equilibria are how organic chemistry became predictive. The lab is substituent, waste and tautomer. This sheet (ORG-21 — Octanol–water log P) is the form associated with log P. Working symbols: $c_{oct}$ , $c_w$ $\rightarrow$ $\log P$ . Hansch's hydrophobic descriptor. Drug-like molecules often sit near log P ≈ 2–3.

Purpose

Purpose: compute

\log P

from

c_{oct}

c_w

in Organic chemistry via

\log P=\log_{10}(c_{\mathrm{oct}}/c_{\mathrm{w}})

log P = log10 (c_oct / c_w). Lipophilicity. Use it when a real organic chemistry question must be answered in SI before a code check.

Live realistic example

In symbols

Live case. Given

c_{oct} = 0.080\,\mathrm{mol/L}

c_w = 0.010\,\mathrm{mol/L}

, the governing relation

\log P=\log_{10}(c_{\mathrm{oct}}/c_{\mathrm{w}})

yields

\log P = 0.903\,\mathrm{—}

. Dilute, 1-octanol/water, concentrations of the same species. Move a slider: the numbers are this situation, not a canned story.

Calculator

Inputs

Octanol concentration c_{oct}0.08 mol/LWater concentration c_w0.01 mol/L

Outputs

log P \log P0.903 —

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Narration of this film

Dilute, 1-octanol/water, concentrations of the same species.

Hansch's hydrophobic descriptor. Drug-like molecules often sit near log P ≈ 2–3.

Reading speed

Watch on YouTube