Class notes
A2 organic chemistry notes
- Course
- Institution
Notes made on benzene, phenol, different A2 mechanisms, and benzene's isomers
[Show more]
Seller
Follow
gsnotes
Reviews received
Content preview
Benzene ringThe benzene ring is six carbon atoms forming a ring of six bonds. Each carbon has a hydrogen
bonded to it in a single bond. In the centre of the ring, delocalised electrons are placed, as
demonstrated by a circle in the middle of the ring. As benzene only consists of carbon and hydrogen
atoms, it is a hydrocarbon molecule. The formula of benzene is C 6H6.
In this model, benzene has p-orbitals on each carbon atom. The p-orbitals extend outwards on each
side of the carbon, allowing electrons to be shared between each p-orbital and to travel between
each orbital in a circle around the molecule. This is shown in the blue and green rings on the diagram
I have drawn above. The p-orbitals are represented by the red figures of eight.
Previously, benzene was presumed by August Kekulé to be a different structure, known as the
Kekulé structure. The Kekulé structure describes benzene as having alternating single and double
bonds between the carbon atoms.
This structure is incorrect for three reasons:
The first limitation of this model is that benzene doesn’t decolourise bromine water. Unsaturated
hydrocarbons are expected to decolourise bromine water, as they are alkenes. Therefore, it is
expected that benzene should decolourise bromine water if it followed the Kekulé model, which
states that benzene has three double bonds.
The second limitation of this model is that the bonds are all the same length in a drawing of the
molecule. Single bonds are known to be 147pm long, and double bonds are known to be 134pm long
when shown under a X-ray microscope. If benzene did follow these rules, then it would take a
slightly skewed hexagonal shape, rather than the even lengths that we see in the Kekulé structure
that forms a perfect hexagon.
The third and final limitation of the Kekulé model is that it has a different enthalpy value than the
one that we see in benzene. The Kekulé model has a much higher and more unstable enthalpy than
benzene has been proved to have. The difference is very large, with the Kekulé model having an
enthalpy value of –360kj/mol and real benzene having a value of –208kj/mol.
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card or Stuvia-credit for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller gsnotes. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for CA$8.06. You're not tied to anything after your purchase.
Can Stuvia be trusted?
4.6 stars on Google & Trustpilot (+1000 reviews)
77333 documents were sold in the last 30 days
Founded in 2010, the go-to place to buy study notes for 14 years now