Summary
Summary Notes 3.3.10 - Aromatic chemistry (A-level only)
- Institution
- AQA
Summary Notes 3.3.10 - Aromatic chemistry (A-level only)
[Show more]
Seller
Follow
Content preview
Taylor’s Notes Aromatic (Arenes) ChemistryBenzene
The term arene includes all compounds with a delocalised π-system These are also called aromatic
compounds with the most common example being benzene (C6H6)
Kekulé suggested the following structure for benzene
Structure and Bonding in Benzene
Structure
Bond C–C C=C All bonds
Length / nm 0.154 0.133 0.139
Using the information above about bond lengths, the Kekulé structure isn’t that accurate as we’d expect 3
C – C bonds (0.154) and 3 C = C bonds (0.133) but instead we have 6 binds which have the same length
(0.149) which is between the C – C and C = C length
The benzene ring is a planar, hexagon, with six electrons in the delocalised π-‘sandwich’ above and below
the ring
The σ-bonds are built up in a similar way to ethene, leaving an unused p orbital on each of the six carbons.
These can overlap sideways in both directions, resulting in a delocalized π-electron cloud, containing six π-
electrons, and stretching over all six atoms, in a ‘sandwich’ which lies above and below the plane of the
ring.
The C – C bonds in benzene are all equal, each of length between a single and double bond
The geometry around each carbon in benzene is trigonal planar and the C – C – C bond angle is 120°
, Taylor’s Notes Aromatic (Arenes) Chemistry
Thermochemical Evidence
Evidence for the ‘delocalised’ structure for benzene is provided by thermochemical evidence
Hydrogenation Reactions
In the presence of a nickel catalyst hydrogen can be added to a double bond
When this is carried out with cyclohexene the following reaction takes place:
The reaction should be used to predict the enthalpy change for a similar reaction for cyclohexa-1,3,5-triene
The predicted enthalpy change for this hydrogenation of benzene is 3(-120) = -360 kJ mol -1
However, the measured value for this hydrogenation of benzene is actually -208 kJ mol -1
Therefore, there is an extra stability associated with the delocalisation of the π electrons in benzene:
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 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 Taylorsnotes. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for £4.99. You're not tied to anything after your purchase.
Can Stuvia be trusted?
4.6 stars on Google & Trustpilot (+1000 reviews)
53340 documents were sold in the last 30 days
Founded in 2010, the go-to place to buy revision notes and other study material for 14 years now