# Why does ring contraction take place in Wagner–Meerwein rearrangement?

An example of Wagner–Meerwein rearrangement given in my textbook is substitution by $$\ce{AgNO2}$$ in iodocyclohexane. One of the product, cyclopentylnitromethane is through ring contraction.

I don't understand how this took place. Can anyone explain the mechanism?

• It would be a mistake to think that a five-member ring is very strained. – Zhe Jun 5 '20 at 15:14
• I know it isn't 'very strained'. I am editing the question. The main question is how is the rearrangement happening. – B.Anshuman Jun 5 '20 at 16:01
• This reference from 1952 claims that the product of the reaction is nitrocyclohexane. No rearrangement. doi.org/10.1021/ja01132a037. A previous study had claimed additionally the formation of 1-methylnitrocyclopentane, which is not cyclopentylnitromethane. What is the name of your textbook? – user55119 Jun 5 '20 at 20:33
• @user55119, S.N.Sanyal - Reactions, Rearrangements and Reagents ; Publisher: Bharti Bhawan ; Page-185. You may find this book online. Also, in your link, it is clearly mentioned that Rosanow discovered rearranged products in 1915, i.e. Wagner-Meerwin Rearrangement is happening – B.Anshuman Jun 5 '20 at 20:58
• I'll post a solution. – user55119 Jun 5 '20 at 23:42