Inductive Effect (I) (-I withdraws electron density through σ; +I donates)

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-I withdraws electron density through σ; +I donates

What each symbol means

SymbolWhat it stands for
+IAlkyl groups (3°>2°>1°>methyl trend for hyperconjugation coupling)
−INO₂, CN, halogens (F>Cl>Br>I), C=O groups

When to use this

Through-bond polarization; falls off with distance; no π bond required.