Stability of benzene

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cupcake4546
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#1
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When textbooks say that benzene is 'more stable' because of x what do they mean by more stable. I'm really confused by this. Could someone explain this please.

e.g Theoretically because there are 3 double bonds in the theoretical cyclohexa-1,3,5-triene one might expect the amount of energy to be 3 times as much as cyclohexene.

However, in actual benzene the amount of energy is less. The 6 pi electrons are delocalised and not arranged in 3 double bonds

The increase in stability connected to delocalisation is called
the delocalisation
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The A.G
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(Original post by cupcake4546)
When textbooks say that benzene is 'more stable' because of x what do they mean by more stable. I'm really confused by this. Could someone explain this please.

e.g Theoretically because there are 3 double bonds in the theoretical cyclohexa-1,3,5-triene one might expect the amount of energy to be 3 times as much as cyclohexene.

However, in actual benzene the amount of energy is less. The 6 pi electrons are delocalised and not arranged in 3 double bonds

The increase in stability connected to delocalisation is called
the delocalisation
Not quite sure what you’re exactly asking, but you just need to know that since the p-orbitals overlap sideways it stabilises the benzene ring producing a delocalised electron ring. Stable just means that more energy is required to break the bonds within the molecule which is caused from the delocalised electron ring that reinforces the bonds within benzene.
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Chemistry tutor
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(Original post by cupcake4546)
When textbooks say that benzene is 'more stable' because of x what do they mean by more stable. I'm really confused by this. Could someone explain this please.

e.g Theoretically because there are 3 double bonds in the theoretical cyclohexa-1,3,5-triene one might expect the amount of energy to be 3 times as much as cyclohexene.

However, in actual benzene the amount of energy is less. The 6 pi electrons are delocalised and not arranged in 3 double bonds

The increase in stability connected to delocalisation is called
the delocalisation
In the context of organic chemistry stable means less reactive. If you compare reactivity of benzene versus alkenes towards bromination, for example. If I add Br2 to alkene it will react immediately and the orange colour will disappear. If I add Br2 to benzene nothing will happen, unless I add a catalyst, namely FeBr3. The reason is delocalization of pi electrons. Basically, this means that the pi electrons in benzene are too busy moving around the ring rather than participate in chemical reactions
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cupcake4546
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(Original post by Chemistry tutor)
In the context of organic chemistry stable means less reactive. If you compare reactivity of benzene versus alkenes towards bromination, for example. If I add Br2 to alkene it will react immediately and the orange colour will disappear. If I add Br2 to benzene nothing will happen, unless I add a catalyst, namely FeBr3. The reason is delocalization of pi electrons. Basically, this means that the pi electrons in benzene are too busy moving around the ring rather than participate in chemical reactions
ahhh thank you this makes sense.
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cupcake4546
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thank you!!

(Original post by The A.G)
Not quite sure what you’re exactly asking, but you just need to know that since the p-orbitals overlap sideways it stabilises the benzene ring producing a delocalised electron ring. Stable just means that more energy is required to break the bonds within the molecule which is caused from the delocalised electron ring that reinforces the bonds within benzene.
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cupcake4546
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(Original post by Chemistry tutor)
In the context of organic chemistry stable means less reactive. If you compare reactivity of benzene versus alkenes towards bromination, for example. If I add Br2 to alkene it will react immediately and the orange colour will disappear. If I add Br2 to benzene nothing will happen, unless I add a catalyst, namely FeBr3. The reason is delocalization of pi electrons. Basically, this means that the pi electrons in benzene are too busy moving around the ring rather than participate in chemical reactions
Wait your saying for it to be stable its less reactive. if something is less reactive, you would need more energy for it to react. but for benzene you need less energy of -208kJ mol-1 and for proposed kekule structure you need more -360kJ mol-1. I think I'm missing something which keeps confusing me
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S9123
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(Original post by cupcake4546)
When textbooks say that benzene is 'more stable' because of x what do they mean by more stable. I'm really confused by this. Could someone explain this please.

e.g Theoretically because there are 3 double bonds in the theoretical cyclohexa-1,3,5-triene one might expect the amount of energy to be 3 times as much as cyclohexene.

However, in actual benzene the amount of energy is less. The 6 pi electrons are delocalised and not arranged in 3 double bonds

The increase in stability connected to delocalisation is called
the delocalisation
The delocalization is what increases stability.
If you look at the theoretical molecule 'Cyclohexa-1,3,5-triene', then that predicts that the enthalpy of hydration is 3(-120) = -360kJ mol-1. However, in actual fact, benzene's is only -208kJ mol-1 which is 152 kJmol-1 less exothermic than the theoretical cyclohexatriene. Because it has less enthalpy of hydration, it is more stable - you can think of this in terms of kinetic energies if that helps (if there's a turbine that is rotating really fast, that is less stable than a turbine that is not rotating so fast [has lower kinetic energy]).

I hope this helps
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cupcake4546
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#8
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(Original post by S9123)
The delocalization is what increases stability.
If you look at the theoretical molecule 'Cyclohexa-1,3,5-triene', then that predicts that the enthalpy of hydration is 3(-120) = -360kJ mol-1. However, in actual fact, benzene's is only -208kJ mol-1 which is 152 kJmol-1 less exothermic than the theoretical cyclohexatriene. Because it has less enthalpy of hydration, it is more stable - you can think of this in terms of kinetic energies if that helps (if there's a turbine that is rotating really fast, that is less stable than a turbine that is not rotating so fast [has lower kinetic energy]).

I hope this helps
thank you!!
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