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FA2202. Delocalization and Conjugation in molecules with > one C = C double bonds. School of Pharmacy Bandung Institutes of Technology. This lecture is about the properties of molecules that have several double bonds and
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FA2202 Delocalization and Conjugation in molecules with > one C = C double bonds School of Pharmacy Bandung Institutes of Technology
. This lecture is about the properties of molecules that have several double bonds and • that depend on the joining up or conjugation of the electrons in these double bonds And see how a large pi framework spread over many atoms and how this dominates the chemistry of such compounds. how this pi framework is responsible for the otherwise unexpected stability of certain cyclic polyunsaturated compounds, including benzene and other aromatic compounds. how this framework gives rise to the many colours in our world.
As you As you look around you, you will be aware of many different colours— from the greens and browns outside to the bright blues and reds of the clothes you are wearing All these colours result from the interaction of light with the pigments in these different things— some frequencies of light are absorbed, others scattered.
. A large pi framework gives rise to the many colours in the world
. Chlorophyll: highly conjugated compound the ring shown in green is fully conjugated
sp3 hybridized orbitals of C • Electron configuration of carbon in its most stable state. • An electron is “promoted” from the 2s orbital to the vacant 2p orbital. • The 2s orbital and the three 2p orbitals are combined to give a set of four equal-energy sp3- hybridized orbitals, each of which contains one electron.
sp2 hybridized orbitals of C Electron configuration of carbon in its most stable state. An electron is “promoted” from the 2s orbital to the vacant 2p orbital. The 2s orbital and two of the three 2p orbitals are combined to give a set of three equal-energy sp2-hybridized orbitals. One of the 2p orbitals remains unchanged.
ethylene the simplest unsaturated compound • The structure of ethene (ethylene) is planar (all atoms are in the same plane) • The carbon atoms are roughly trigonal • the C= C bond distance is shorter than that of a C–C sigma bond.
combination of two sp2orbitals of C atoms in formation of acethylene
No rotation is possible about a double bond • The π bond has electron density both above and below the σ bond as the parallel p orbitals overlap locking the bond rigid. • - π bond must be broken before rotation can occur.
sp hybridized orbitals of C (a) Electron configuration of carbon in its most stable state. (b) An electron is “promoted” from the 2s orbital to the vacant 2p orbital. (c) The 2s orbital and one of the three 2p orbitals are combined to give a set of two equal-energy sp-hybridized orbitals. Two of the 2p orbitals remain unchanged.
Conjugated double bond ‘conjugated’ : ‘joined together, especially in pairs’ ‘acting or operating as if joined’. the properties of a conjugated system are often different from those of the component parts. We are using the word conjugation to describe bonds and delocalization to describe electrons.
Distinct characteristic of aromatic double bonds Benzene does react with Br2 in the presence of iron(III) bromide as a catalyst, but even then addition isn’t observed. Benzene and its derivatives reflect a special stability Substitution occurs instead!
Drawing reaction mechanism for benzene structure it does not matter which way round you draw the benzene ring – both drawings give the same result but one uses more arrows to get there
