Thread: 1,3,5 cyclohexatriene?

Is there such a thing as 1,3,5 cyclohexatriene (hope I named it correctly), or does a six-membered ring structure with alternating single and double bonds automatically take on the resonance structure of benzene (thus losing the distinction between its single and double bonds)?

A six-membered ring structure with alternating single and double bonds is benzene. And yes, it always loses its distinction between its single and double bonds. I suppose you can also call it 1,3,5-cyclohexatriene if it amuses you, in the same way that we can refer to water as dihydrogen monoxide.

Originally Posted by SteveF

A six-membered ring structure with alternating single and double bonds is benzene. And yes, it always loses its distinction between its single and double bonds. I suppose you can also call it 1,3,5-cyclohexatriene if it amuses you, in the same way that we can refer to water as dihydrogen monoxide.

Except to me calling it 1,3,5-cyclohexatriene (and not benzene) seems to imply that the bonds are fixed, which they are not. My point was kind of just to see if the resonance is really caused by that particular configuration of bonding, or if you could have that configuration with fixed bonds, with something else causing the resonance, if you see what I mean.

Your idea goes back to 1865, when Kekule first propsed the resonant structure of benzene that we accpet today. At the time he met strong objections from his colleagues opposed to the idea of resonance. They insisted on the 1,3,5-cyclohexatriene as you proposed, and claimed the single and double bonds were fixed.

To test the idea they chlorinated benzene to 1,2-dichlorobenzene. If the 1,3,5-cyclohexatriene model were correct they would be able to find two isomers, one in which the chlorine atoms were attached to a pair of single-bonded carbon atoms, and another in which they were attached to two double-bonded atoms. Naturally, they found only one isomer.

These experiments confirmed Kekule's model and established the resonance theory. As a side benefit, the intense interest in the project helped launch the great German chemical industry in the 19th century.
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Originally Posted by SteveF

Your idea goes back to 1865, when Kekule first propsed the resonant structure of benzene that we accpet today. At the time he met strong objections from his colleagues opposed to the idea of resonance. They insisted on the 1,3,5-cyclohexatriene as you proposed, and claimed the single and double bonds were fixed.

To test the idea they chlorinated benzene to 1,2-dichlorobenzene. If the 1,3,5-cyclohexatriene model were correct they would be able to find two isomers, one in which the chlorine atoms were attached to a pair of single-bonded carbon atoms, and another in which they were attached to two double-bonded atoms. Naturally, they found only one isomer.

These experiments confirmed Kekule's model and established the resonance theory. As a side benefit, the intense interest in the project helped launch the great German chemical industry in the 19th century.
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Good background info. Thanks, much appreciated.