Illustrated Glossary of Organic Chemistry

Enthalpy of formation (heat of formation; ΔH_f^o): The hypothetical enthalpy change (ΔH) when a substance is synthesized from the corresponding elements in their standard states. A more negative (or less positive) enthalpy of formation indicates a more stable isomer.

4 C (graphite) + 3 H₂ (gas)			1,3-Butadiene: ΔH_f^o = 29.9 kcal mol^-1

4 C (graphite) + 3 H₂ (gas)			Methylene cyclopropane: ΔH_f^o = 47.7 kcal mol^-1

ΔH_f^o 1,3-butadiene < ΔH_f^o methylene cyclopropane, so 1,3-butadiene is more stable than methylene cyclopropane.

Related terms: Enthalpy of hydrogenation, heat of hydrogenation, enthalpy of combustion, heat of combustion, conjugation, aromaticity, Gibbs free energy, energy of activation, ΔΕ, ΔΕΝ, ΔG, ΔG⁺⁺, ΔS
Wikipedia entry
Return to glossary index