ORG-04

Woodward–Fieser snapshot

λmax ≈ base + 5 n_alkyl + 30 n_exo. Diene UV estimate.

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SpectroscopyWoodward–Fieser

Governing equation

\lambda_{\max}=\lambda_0+5n_{\mathrm{alk}}+30n_{\mathrm{exo}}

where

\lambda_0: Parent base (nm)
n_{alk}: Alkyl substituents (—)
n_{exo}: Exocyclic double bonds (—)
\lambda_{max}: Estimated λmax (nm)

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-04 — Woodward–Fieser snapshot) is the form associated with Woodward–Fieser. Working symbols: $\lambda_0$ , $n_{alk}$ , $n_{exo}$ $\rightarrow$ $\lambda_{max}$ . Empirical increments on a parent diene (heteroannular 214 nm, homoannular 253 nm).

Purpose

Purpose: compute

\lambda_{max}

from

\lambda_0

n_{alk}

n_{exo}

in Organic chemistry via

\lambda_{\max}=\lambda_0+5n_{\mathrm{alk}}+30n_{\mathrm{exo}}

λmax ≈ base + 5 n_alkyl + 30 n_exo. Diene UV estimate. 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

\lambda_0 = 214.000\,\mathrm{nm}

n_{alk} = 2.000\,\mathrm{—}

n_{exo} = 1.000\,\mathrm{—}

, the governing relation

\lambda_{\max}=\lambda_0+5n_{\mathrm{alk}}+30n_{\mathrm{exo}}

yields

\lambda_{max} = 254.0\,\mathrm{nm}

. Enter base (nm) and alkyl / exocyclic counts. Move a slider: the numbers are this situation, not a canned story.

Calculator

Inputs

Parent base \lambda_0214 nmAlkyl substituents n_{alk}2 —Exocyclic double bonds n_{exo}1 —

Outputs

Estimated λmax \lambda_{max}254.0 nm

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Narration of this film

Enter base (nm) and alkyl / exocyclic counts.

Empirical increments on a parent diene (heteroannular 214 nm, homoannular 253 nm).

Reading speed

Watch on YouTube