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# A2 - Kekule's model / benzene

1. Can someone explain the part about carbon-carbon bond lengths in:
Kekule's model
Benzene

And also can you explain the actual lengths of C-C and C=C bonds in regular compounds, like alkanes/alkenes.

The book is a little on this part, for me atleast.

Thanks a bunch!
2. The Carbon carbon bonds are half way between C-C and C=C in length. (are intermediate in length)

Implying there is '1 and a half bonds' in benzene, hope that helps!
3. Oh okay, so in benzene the carbon to carbon bonds are all the same length, and that length is in between the length of C-C and C=C bonds?.. 0.139 according to the book..
What about the Kekule model, what does that say about the bond lengths, and what about C-C and C=C bond lengths in general?

Thanks
4. (Original post by Kasam)
Can someone explain the part about carbon-carbon bond lengths in:
Kekule's model
Benzene

And also can you explain the actual lengths of C-C and C=C bonds in regular compounds, like alkanes/alkenes.

The book is a little on this part, for me atleast.

Thanks a bunch!
If the actual structure of benzene were to be alternating double C=C and single C-C bonds, like in the Kekule structure, you would expect there to be two different bond lengths in benzene.

However, spectroscopic studies show that there is only one C-C bond length.

In benzene C-C is 0.139 nm

normal C-C bonds are 0.154 nm
and C=C bonds are 0.134nm

hence the bond length in benzene is intermediate between single and double bonds.
5. (Original post by Kasam)
Can someone explain the part about carbon-carbon bond lengths in:
Kekule's model
Benzene

And also can you explain the actual lengths of C-C and C=C bonds in regular compounds, like alkanes/alkenes.

The book is a little on this part, for me atleast.

Thanks a bunch!
The carbon carbon bond lengths in Kekule's model are in between the lengths of an alkane and and alkene's bond length. This is unusual because Kekule suggested that there are 3 double bonds and 3 single bonds, therefore you would EXPECT there to be 3 bonds the same size and the other 3 bonds the same size but this isn't the case as all 6 c-c bonds in benzene are in between the length of an alkane and alkene's bond length.

hope that helps!
6. Thanks to both of you, I think I get it now

The book just had to explain it the difficult way!

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