Kekulé Structures

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Camille Marangi 2E
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Joined: Fri Sep 28, 2018 12:26 am

Kekulé Structures

Postby Camille Marangi 2E » Tue Jan 29, 2019 1:37 pm

So 4E.9 from 7th edition reads as follows:

Benzene is more stable and less reactive than would be predicted from its Kekulé structures. Use the data in Table 4E.3 to calculate the lowering in molar energy when resonance is allowed between the Kekulé structures of benzene.

Am I supposed to assume a kekulé stucture would just be benzene without resonance? Not sure what to make of this so any insight would greatly help. Thanks!

Tam To 1B
Posts: 72
Joined: Fri Sep 28, 2018 12:25 am

Re: Kekulé Structures

Postby Tam To 1B » Tue Jan 29, 2019 10:26 pm

For this problem, they are just asking you to compare the differences between the bond enthalpies of benzene.
In one structure, you have benzene with 3 C-C and 3 C=C bonds. Using the table, this would mean (3*348) + (3*612) = 2880 kJ.
However, benzene in its resonance structure has 6 C-C/C=C bonds (indicated with dots above a line) on the table). Using the table values, this would be 6*518 = 3108 kJ.
The difference between these values gives you 228 kJ.

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