ORG-17

Beer–Lambert (organic) A = ε l c

A = ε l c. Absorbance of a chromophore in a cuvette.

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SpectroscopyBeer–Lambert

Governing equation

A=\varepsilon \ell c

where

\varepsilon: Molar absorptivity (L mol^{-1} cm^{-1})
\ell: Path (cm)
c: Concentration (mol/L)
A: Absorbance (—)

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-17 — Beer–Lambert (organic) A = ε l c) is the form associated with Beer–Lambert. Working symbols: $\varepsilon$ , $\ell$ , $c$ $\rightarrow$ $A$ . ε is the molar absorptivity (L mol⁻¹ cm⁻¹). Linear only in the dilute, non-scattering limit.

Purpose

Purpose: compute

A

from

\varepsilon

\ell

c

in Organic chemistry via

A=\varepsilon \ell c

A = ε l c. Absorbance of a chromophore in a cuvette. 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

\varepsilon = 12000.000\,\mathrm{L mol^-1 cm^-1}

\ell = 1.000\,\mathrm{cm}

c = 5.000e-5\,\mathrm{mol/L}

, the governing relation

A=\varepsilon \ell c

yields

A = 0.6000\,\mathrm{—}

. 1 cm path default, single wavelength. Move a slider: the numbers are this situation, not a canned story.

Calculator

Inputs

Molar absorptivity \varepsilon12000 L mol^{-1} cm^{-1}Path \ell1 cmConcentration c0.00005 mol/L

Outputs

Absorbance A0.6000 —

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Narration of this film

1 cm path default, single wavelength.

ε is the molar absorptivity (L mol⁻¹ cm⁻¹). Linear only in the dilute, non-scattering limit.

Reading speed

Watch on YouTube