Lecture notes
Lecture notes Unit 14B - Applications of Organic Chemistry
- Institution
- PEARSON (PEARSON)
Seasonal written in 2021
[Show more]
Seller
Follow
Content preview
Unit number and title Unit 14: Applications of Organic ChemistryLearning aim B: Understand the reactions and properties of aromatic
compounds.
Assignment title Aromatic ring chemistry for designer chemicals
THE STRUCTURE OF BENZENE
The normal structure of the benzene ring is 6 carbon and hydrogen atoms represented
by a hexagon and all being the exact same length between the single bond, each
carbon represented by the corner is also bonded with one another atom, as their
delocalised electron, the accepted benzene rings formulae are C6 H.
The carbon atom forms a different bond with the two similar carbon
atoms during the hybridisation process because it has an SP2 state
due to the s orbital and the two p orbitals, the three sp2 orbital
arrangements. The accepted structure if the benzene rings 6 sigma
and 3 pi bonds that alternate, each carbon atom arrangement has 4
electrons within the bond in the electrons pairs, 3 of them are in a
sigma bond while one contributes to the pi bond.
● The diagram shows 2 delocalised electrons which could be found anywhere.
● The presence of delocalised electron keep the benzene ring stable
The hybridisation occurs only
when three carbins join each
other once the carbon atoms
have been hybridised with only
,three orbitals rather than 4 the uses of 2s electrons and 2p electrons but then leave 2p
electrons unchanged.
The benzene ring does not react with additional reactions because it would mean the
breaking of delocalised electrons and the loss of stability. Instead, the accepted
structure represents itself by a circle in the middle that shows the delocalised electrons
and each corner of the hexagonal shape acquires carbon atoms with hydrogen attached
to each one.
An introduction to arenes (aromatic hydrocarbons).
The benzene ring has a regular hexagonal shape, with all of the bonds at an angle of
120* because they are all the same length, and it also has a hexagonal shape because
the bonds are identical. Because of the delocalized electrons, the bonds do not
alternate between double and single bonds. It is significant as the planar because it is
the only way that a p orbital can overlap it sideways to produce a pi system.
Kekule’s structure of the benzene ring is considered wrong since the new benzene ring
with delocalised electrons has been revealed. As the accepted structure is much more
stable compared to the kekule’s structure. As the kekule’s structure has alternating
double carbon bonds and a single carbon bond. This kekule’s attempt of the benzene
ring had been accepted by the people of that time however once new evidence was
found people started to question that very kekule’s structure, then a proposal of a new
mode of the benzene ring was invented and since then it has been considered the
accepted structure.
Evidence for X-ray
Single X rays patterns of a single carbon-carbon bond length of cyclohexene were
measured 0.154nm. The length of the double bond on the carbon bonds cycleohens is
also measured at 0.133nm. If the kekule structure was still in use both the double bond
of the carbon-carbon and a single carbon-carbon and if that's true the bond would
have different length meaning it will be less stable. The same technique had been used
on the approved structure to calculate and it equal to 0.139nm therefore there can not
be any alternative bond and all the evidence of the kekule structure is going against due
to the unstable structure.
, Evidence for distributed isomers
If keule structure cyclotriene of the structure of the benzene ring, also of the reactive
double Carbon-Carbon bonds, a chlorine molecule should develop. During tests,
however, only three disubstituted isomers and one monosubstituted product are
generated when Benzene is
combined with a Chlorine molecule.
This data implies that Benzene
lacks double Carbon-Carbon
bonds, refuting Kekulé's structure
of alternating double and single
Carbon-Carbon bonds.
Evidence for thermochemical
One mole of gaseous Benzene
having Kekule structure, the
predicted enthalpy of production
from its constituent constituents of
Carbon and Hydrogen in their
standard states is +252 Jmol-1.
When the actual energy of
formation was measured, it was
found to be far lower, at just
+82KJmol-1. This indicates that
Benzene's structure is substantially
more stable than Kekulé's model.
The expected enthalpy change for
the hydrogenation of Benzene
when cyclohexene, with its one
double Carbon-Carbon bond, undergoes hydrogenation is -119.6KJmol-1, providing
more thermo - chemical evidence against Kekules concept. By multiplying the
approximate value for the hydrogenation of cyclohexene by three, the theoretical
change in enthalpy for the hydrogenation of benzene may be computed.
According to Kekulé's model, benzene contains three double Carbon-Carbon bonds,
giving it a value of -358.8KJmol-1.
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 sethimohammed78638. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for £5.49. You're not tied to anything after your purchase.
Can Stuvia be trusted?
4.6 stars on Google & Trustpilot (+1000 reviews)
73918 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