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Thursday

4th September

Chemistry:

·

Benzene

·

C=C bond is shorter than a C-C bond, but benzene is perfectly hexagonal as all six carbon bonds have the same length, intermediate between that of

a single and that of a double bond

·

In a

circular pi bond the electron density is evenly distributed through a pi bond

above and below the ring

o The single bonds are formed with electrons in

line between the carbon nuclei which are called sigma bonds

o Double

bonds consist of a sigma bond and a pi bond

§ The pi bonds are formed from overlap of atomic p-orbitals above and below the

plane of the ring

§ Since the electrons are out of plane of the

atoms, these orbitals can interact with each other freely and become

delocalized, therefore instead of being tied to one atom of carbon, each

electron is shared by all six in the ring

§ Thus there are not enough electrons to form

double bonds on all the carbon atoms, but the extra electrons strengthen all of

the bonds on the ring equally and the

resulting molecular orbital has pi symmetry

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