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BICYCLO Nomenclature

 BICYCLO Nomenclature

Bicyclo is a prefix used in organic chemistry nomenclature to describe a specific type of fused ring system where two non-adjacent carbon atoms are shared between two rings. This prefix is followed by numbers and letters to denote the arrangement of the rings and the positions of substituents.
Basic Structure: A bicyclo compound consists of two rings that share two carbon atoms. These two carbon atoms are called bridgehead carbons, and they are not part of the individual rings.

Bicyclo Prefix: The bicyclo prefix is followed by two numbers separated by a dot (e.g., bicyclo[2.2.1]). These numbers indicate the number of carbon atoms in each ring and the number of carbon atoms in the bridge connecting the two rings, respectively.

  • The first number represents the number of carbons in the first ring.
  • The second number represents the number of carbons in the second ring.
  • The third number represents the number of carbons in the bridge connecting the two rings.
first, is to start numbering from one of the bridgehead carbon atoms.
then,  rings are numbered according to their size. numbering starts from the ring having more carbon atoms.
In bridged and fuse structure we use word Bicyclo and add square brackets while naming.
If we don't have carbon in between the bridge then we add zero as in example below.
If substituent is added and both rings have same carbon atoms then we give substituent the lowest possible number and name of substituent is written before bicyclo and parent name as shown in picture below.


If substituent is attached to two different size of bridged rings incase of bicyclo then numbering should be given to the ring having more carbon atoms but in a way that gives lowest possible number to the substituent as shown below.


Ring priority:

Priority 1 is given to the large bridge ring.
then, If we have bridge rings of same size as shown below other than large ring then we give priority 2 to the bridge ring having substituent and priority 3 is given to the bridge ring having no substituent despite of same size.

If same number of carbons are present in rings, then, we look for substituents to give priority.
if substituents are attached to both bridge rings then we give priority according to alphabetical order as shown in example below.
priority 1 is the bridge ring having more carbons. Ring 2 and 3 have same carbons but both have substituents attached. In alphabetical order ethyl E comes first then methyl m, so, the ring having ethyl substituent is given priority 2 and ring having methyl is given priority 3.
In below examples, two bridge rings having same number of carbons but priority 1 is given to the ring having more carbons as well as substituent.
In the eaxample given below, methyl is given priority BECAUSE it is near the bridged head carbon while ethyl as far away so, it is getting priority 2.

Practice Problems


    8
Functional group given more priority
substituent near bridge carbon is given more priority



  5. carboxylic acid given more priority then hydroxyl group


























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