What is the product of reaction 1,1'-bi(cyclopent-1-en-1-yl) with O3?

Question

And my second question what is the product of reaction 1,1'-bi(cyclopent-1-en-1-yl) with NBS? I'm quite confused since it's bicycle and there are 2 double bonds. Here's the link of the structure: https://ibb.co/fSfx8K

Answer 1

Hello Simona

 

O₃ is a reaction called ozonolysis, where the C=C double bond breaks and gets oxidized to form a mixture of aldehydes and ketones (depending on the starting structure).

 

If one of the carbons of the C=C double bond has 2 substituents on it, then it will form a ketone whereas if the C=C double bond has 1 substituent OR is unsubstituted, then you will form an aldehyde.

 

An example:

 

H₃C  CH₃                        O                           O

     l     l                              ll                             ll

    C=C    + O₃ → H₃C−C−CH₃   +   H₃C−C−H

     l     l

H₃C  H                          ketone                aldehyde

 

When you have a cyclic ring with a C=C, the same type of oxidation occurs like a straight chain alkene.  However, unlike a straight chain alkene that breaks apart into 2 separate products, the carbons in a cyclic alkene are still connected after oxidation.

 

For instance, if you oxidize unsubstituted cyclopentene, you will form a 5-carbon dialdehyde as the only product.

 

Cyclopentene + O₃ → OHC−CH₂−CH₂−CH₂−CHO (Pentanedial)

 

 

For the ozonolysis of 1,1'-bi(cyclopent-1-en-1-yl), you have two 5-membered rings connected by a C-C single bond.  This C-C single bond will keep all the carbon atoms connected together after the double bonds on both rings get oxidized.

 

Notice that on each C=C, one side of the double bond has an H on it and the other does not.  The part of the double bond with an -H on it will get oxidized to an aldehyde and the other part of the double bond will get oxidized to a ketone.  Both double bonds get oxidized to a di-aldehyde and a di-ketone.  The two aldehyde functional groups will be at each end of the molecule.

 

It is difficult to show the oxidation process here since a Chem draw feature is not available in this forum.  I will draw the final structure below, and using the information above, you can write the oxidation process down for yourself.

 

OHC−CH₂CH₂CH₂−C(=O)−C(=O)−CH₂CH₂CH₂−CHO 

 

Name of this compound is 5,6-Dioxo-decanedial.  Carbon #'s for the 2 aldehyde groups are not needed in the name since they are expected to occupy the two ends of the molecule.

 

Reaction #2

 

NBS stands for N-bromosuccinimide.  It is used to brominate an alkene at the allylic position, which is the carbon adjacent to the C=C double bond.  This reaction proceeds via a free radical bromination mechanism and for bromination to occur, the adjacent carbon must have a hydrogen (-H) bonded to it.

 

-C=C-CH (end carbon is allylic).

 

1,1'-bi(cyclopent-1-en-1-yl) has 4 allylic carbons, therefore, it can be predicted that you will get a mixture of mono-, di-, tri-, and tetra-brominated products.

 

Hope the above was helpful!