Integrated SequencePhysics Chemistry Organic Biology

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Purdue University - Resonance Hybrids
Concise description of resonance.

Chem1 Virtual Textbook - Too many structures: resonance hybrids
Presentation of resonance in the context of Lewis structures but which expands to a very readable introductory quantum mechanical explanation of resonance stability.

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Work, Energy, and Power


The Chemical Bond


The Second Law of Thermodynamics and Heat Engines

The π orbitals of an extended sequence of sp2 hybridized atoms may combine to form a π system, wherein electrons are delocalized through orbital hybridization over a large number of atoms. Such resonant forms are lower energy, i.e. more stable than non-conjugated systems.

Why is that so. A simplistic way of looking at it is to say that extended conjugation allows electron charge to spread out and decrease in potential energy, a simplistic, but useful way of looking at it.

A more complete way is to say that in addition to the decrease in electrostatic potential energy, there is also greater 'quantum multiplicity' in extended hybrid orbitals.

For both of these reasons, resonance hybridization decreases the free energy of a molecular form, making it more stable.

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