Bicyclic and Polycyclic compounds | Nomenclature and details | Explained by IITian | Mains, Advanced - Videos

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Hello Guys, today we are going to discuss bicyclic and polycyclic compounds in great details.
The naming of bridged bicycles has its own special kind of funk. Unlike the molecules you’ve likely come across so far, which will have a clear “longest chain” or “largest ring” to start from, trying to find the place to start based on those criteria alone will likely have you going in circles. Instead, bridged bicycles are named according to a unique system of their own. based on the length of their bridges, and then the overall number of carbons in the bicycle. The steps below walks through the process:-

Bicyclic compounds:-

1. Locate the bridgehead carbons, the carbons part of two rings.

2. Now, identify the three connections between the 2 bridgeheads, called bridges: arrange these in decreasing order of number of carbon atoms (excluding the bridgehead). Say these three numbers are m, n, o [m greater than n greater than o].
3. Write the name of your compound as: bicyclo[m.n.o]”m+n+o+2″alkane.
4. In case there is a substituent or a functional group is present, you need to number your carbons: start from of the bridge-head, through the longest bridge to the shorter and then the shortest (if any).

Spirocyclic compounds:-

Locate the bridgehead carbon, the only carbon part of the two rings.
Now, spot the two ring systems having having 2 or more carbons: arrange these in increasing order of number of carbon atoms (excluding the bridgehead, again). Say these three numbers are p,q [p greater than q].
Write the name of your compound as: spiro[p.q]”p+q+1″alkane.
In case there is a substituent or a functional group is present, you need to number your carbons: start from of the atom next to bridgehead in the smaller ring, through the bridgehead carbon to the bigger ring.
Naming of others polycyclic compounds like Anthracene, Phenenthrene, Steroids etc has been discussed in details.

Enjoy the lecture.
Good luck
Thanks
Team IITian Explains
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42 COMMENTS

  1. Sir,steroids ka nomanclature kysa hoga wo toh nhi bataye aap…4 ring hai toh kya tetracyclo likhna parega? Or [ ] brackets e aander kya likhein?

    Sir plz rply,last one ka nomanclature bata dijiye…..and Thank you very much for such conceptual vdos in very easy and straight forward manner.

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