4.isoprene rule

it is about a isoprene rule

1. Isoprene rule Prepared by Dr. N.GOPINATHAN ASSISTANT PROFESSOR DEPARTMENT OF PHARMACEUTICAL CHEMISTRY FACULTY OF PHARMACY SRI RAMACHANDRA UNIVERSITY CHENNAI-116 TAMILNADU INDIA

2. 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.

3. The empirical formula is C5H8. On thermal decomposition yield isoprene. Isoprene undergoes polymerisation to yield various terpenoid .

4. 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

5. Another end as tail According to special isoprene rule the isoprene unit in terpenoids are linked in head to tail fashion

6. 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

7. The skeleton which donot follow isoprene rule are generally rejected

8. 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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