Question

A mixture of all isomers of pentane is allowed to react with chlorine radicals (produced by photochemical cleavage of $$C{l}_2$$). How many different isomeric alkyl radicals can form by hydrogen abstraction in the following reaction?
$$Pentane\left(allisomers\right)+Cl\ast \to Pentylradicals\left(allisomers\right)+HCl$$
A. 5
B. 6
C. 7
D. 8

Answer 1

Hint:We must remember that the pentane $$\left(C_5{H}_{12}\right)$$ is an organic compound and an alkane with five carbon atoms. Hence, pentane has three structural isomers. These are n-pentane, isopentane, and neo-pentane. When we react with chlorine radical’s pentane gives three radicals, isopentane gives four radicals, and neopentane gives one radical. So a total of eight alkyl radicals can form by hydrogen abstraction.

 Complete step by step answer:
Initially, we must understand about isomers of pentane. Isomers are nothing that has the same molecular formula and different structures. Therefore, pentane having three isomeric forms namely n-pentane, isopentane, and neopentane.
      

We must know that the radical reactions commonly observed with chlorine and bromine. In this reaction, the first step will be the initiation step and second step is the propagation step and gives multiple possible products.
We must understand that the reaction of each isomeric pentane that reacts with chlorine radical gives a different number of characteristic radicals based on the isomers. Therefore, we react the n-pentane with chlorine radicals that give three different characteristic radicals.

                                                    

We can understand that the isopentane also reacts with chlorine radicals which give four different isomers in a product.

                     

Finally, the neopentane isomers also react with chlorine radicals giving the one neopentane radicals. Therefore, we get eight isomeric radicals for the pentane compound.
  

Therefore, we can understand that the pentane molecule that reacts with chlorine radicals gives eight different alkyl isomeric radicals.

So the option (A) is the correct answer.

Note:
We must have to know that the radical halogenation could result in a mixture of multiple products. That's because there are different hydrogen atoms that could be extracted in the first propagation step. Abstracting a hydrogen atom from the middle carbon of pentane would lead ultimately to one product. Abstracting a hydrogen atom from either of the end carbons of pentane would lead to formation of another different product.