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unit 14.2 Aromatic ring chemistry for designer molecules
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Unit 14 Applications of organic chemistry Title: Aromatic ring chemistry for designer molecules
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Aromatic ring chemistry for designer chemicalsIntroduction
Aromatic hydrocarbons include arenes. Originally used to describe their pleasant scents, the term
"aromatic" is now used to describe a specific type of delocalized bonding. The most basic is benzene,
C6H6. The next most basic is methylbenzene, often known as toluene, which has a methyl group in
place of one of the hydrogen atoms that were originally linked to the ring. - C 6H5CH3.
Structure of benzene
Benzene has the chemical formula C6H6, meaning it has six carbon atoms and six hydrogen atoms.
Three double bonds and a six-carbon ring, symbolised by a hexagon, are present in the structure. A
corner that is bonded to other atoms represents the carbon atoms.
Promotion of an electron
There is only a small energy gap between the 2s and 2p orbitals, and an electron is promoted from
the 2s to the empty 2p to give 4 unpaired electrons. The extra energy released when these electrons
are used for bonding more than compensates for the initial input.
Hybridisation
Because each carbon is only joining to three other atoms, when the carbon atoms hybridise their
outer orbitals before forming bonds, they only need to hybridise three of the orbitals rather than all
four. They use the 2s electron and two of the 2p electrons but leave the other 2p electron
unchanged.
, Because a s orbital and two p orbitals reorganised to create the new orbitals, they are known as sp2
hybrids. The three sp2 hybrid orbitals align themselves as far apart as they can, which is at a plane
angle of 120° to one another. At an angle to them is the final p orbital.
Now, each carbon atom resembles the illustration on the right. All of this occurs in ethene as well.
Each carbon atom in benzene is connected to two additional carbon atoms that are comparable to it,
as opposed to only one. Each carbon atom forms sigma bonds with two additional carbon atoms and
one hydrogen atom by means of sp2 hybrids. The sigma bonds created are depicted in the following
diagram, which for the time being ignores the p orbitals. Each carbon atom has a p electron that
overlaps with electrons on both sides of it. A system of pi bonds that are dispersed throughout the
entire carbon ring are produced by the significant sideways overlap. Since there are now more than
simply two carbon atoms holding the electrons together, yet
The sigma bonds are represented in the diagram as plain lines to make it easier to understand. One
molecular orbital is represented by the two rings above and below the molecule's plane. Each of the
rings contains one of the two delocalized electrons. The remaining four delocalized electrons are
housed in two comparable (but distinct) molecular orbitals. The strongest covalent link that results
from atomic orbitals overlapping directly is known as a sigma bond. These connections are invariably
the initial covalent bond type to be discovered between two atoms.
Pi bonding
Due to the benzene ring's pi electrons' slight electrophilicity, they have the potential to attack the
partly positive carbon and produce a non-aromatic intermediate (note that this intermediate has
several resonance structures, so that it is not as unstable as it might appear). The aromaticity of the
ring is restored by the removal of a proton, and the aluminium trichloride catalyst is regenerated
along with a hydrochloric acid molecule. An important note regarding this reaction is that because
the aluminium trichloride creates what is basically a carbocation, rearrangements can take place to
create a more highly substituted carbocation.
For instance, instead of the result you might originally anticipate, 1-Chloro-2-Methylpropane added
to benzene with aluminium trichloride produces t-butyl benzene (figure out the reaction).
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