Year 12s: what will be the first way you research your future options? >>

A2 - Kekule's model / benzene

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 :confused:

on this part, for me atleast.

Thanks a bunch! :biggrin:

Reply 1

ZeeBurb

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!

Reply 2

Kasam

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 :smile:

Reply 3

charco

Study Forum Helper

Original post by Kasam

on this part, for me atleast.

Thanks a bunch! :biggrin:

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.

Reply 4

Issy123

Original post by Kasam

on this part, for me atleast.

Thanks a bunch! :biggrin:

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. :smile:

hope that helps!

Reply 5

Kasam