Structure (hybridization, bonding, resonance...)

ChemInteractive

Description: 

ChemInteractive is a 'tutorial' site for students of organic chemistry.  It provides practice problems for self-guided learning.  Students must construct their answers by drawing structures and mechanisms, and 'chemically intelligent' feedback is provided to help learners understand how to solve the problems.  Links to other free learning resources are included.

Why is 1,4-cyclohexadiene stable?

Author(s): 
Daniel J. Berger
Author Affiliation: 
Bluffton University
Abstract: 

Why is 1,4-cyclohexadiene stabilized? Using qualitative perturbation theory to teach conjugation

 

Six-carbon polyenes display quite regular properties, when one compares their stabilities using hydrogenation enthalpies. Each double bond in a conjugated system is worth about 10 kJ/mol in resonance energy, and non-conjugated dienes show no resonance energy. Cyclohexadienes are puzzling: 1,3-cyclohexadiene is less stable, and 1,4-cyclohexadiene is more stable, than corresponding open-chain dienes. Qualitative molecular orbital perturbation theory can be used to explain these anomalies.