4.isoprene rule
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Transcript of 4.isoprene rule
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Isoprene rulePrepared by
Dr. N.GOPINATHANASSISTANT PROFESSOR
DEPARTMENT OF PHARMACEUTICAL CHEMISTRYFACULTY OF PHARMACY
SRI RAMACHANDRA UNIVERSITYCHENNAI-116TAMILNADU
INDIA
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• In 1887 wallach enunciated isoprene rule i.e the skeleton structures of all naturally occurring terpenoids are build up of isoprene units.
• All terpenoids derived from one monomeric structural unit, isoprene hence they are referred as isoprenoid compounds.
CH2
CH3
CH22-methylbuta-1,3-diene
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• The empirical formula is C5H8.• On thermal decomposition yield
isoprene.• Isoprene undergoes polymerisation to
yield various terpenoid.
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• There is a special type of arrangement were found in all terpenoid.
• Ingold in 1925 formulated this observation under rule.
• It is based on how isoprene units in terpenoids are linked together.
• The branched end of the isoprene unit is considered as head
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• Another end as tail
According to special isoprene rule the isoprene unit in terpenoids are linked in head to tail fashion
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The basic carbon skeleton of a mono terpenoid Is as follows according to isoprene rule
Special isoprene rule is a very suitable tool to limit the number of carbon skeletons of the structure of known terpenoid
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The skeleton which donot follow isoprene rule are generally rejected
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It is only used as guiding principle and not as a fixed rule.It is summary of experience and natural law.There are deviation and violation of it
Exception – Crypton a natural terpenoid contains only nine carbon atom instead of ten hence isoprene rule cannot be applied to this
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THANK YOU