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

coct∈[1×10−8,2]c_{oct} \in \left[1\times 10^{-8}, 2\right]

where

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

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①

Governing law — red

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

coct∈[1×10−8,2]c_{oct} \in \left[1\times 10^{-8}, 2\right]

coct=1×10−8c_{oct} = 1\times 10^{-8}log⁡P=−6\log P = -6

②

Domain of the variable — blue

c_{oct}_{\min} = 1\times 10^{-8},\quad c_{oct}_{\max} = 2

coct∈[1×10−8,2]c_{oct} \in \left[1\times 10^{-8}, 2\right]

coct=1×10−8c_{oct} = 1\times 10^{-8}coct=1×10−8c_{oct} = 1\times 10^{-8}

③

Response curve — green

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

coct∈[1×10−8,2]c_{oct} \in \left[1\times 10^{-8}, 2\right]

coct=1×10−8c_{oct} = 1\times 10^{-8}log⁡P=−6\log P = -6

④

Rate of change — amber

dlog⁡Pdcoct\frac{\mathrm{d}\log P}{\mathrm{d}c_{oct}}

coct∈[1×10−8,2]c_{oct} \in \left[1\times 10^{-8}, 2\right]

coct=0.013c_{oct} = 0.013log⁡P′=254.4\log P^{\prime} = 254.4

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: coctc_{oct}, cwc_w →\rightarrow log⁡P\log P. Hansch's hydrophobic descriptor. Drug-like molecules often sit near log P ≈ 2–3.

Purpose

Purpose: compute log⁡P\log P from coctc_{oct}, cwc_w in Organic chemistry via log⁡P=log⁡10(coct/cw)\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 coct=0.080 mol/Lc_{oct} = 0.080\,\mathrm{mol/L}, cw=0.010 mol/Lc_w = 0.010\,\mathrm{mol/L}, the governing relation log⁡P=log⁡10(coct/cw)\log P=\log_{10}(c_{\mathrm{oct}}/c_{\mathrm{w}}) yields log⁡P=0.903 —\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

Outputs

  • log P \log P0.903 —
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ORG-21 · phase
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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