Monday, 9 November 2015

stereochemistry - Monochlorination of 2-chloropentane and possible enantiomer products


I found a question to determine the number of possible chiral products of monochlorination of 2-chloropentane.So, first the products are (with possible number of enantiomers in the parentheses:


2,2-dichloropentane(no chiral product),


1,2-dichloropentane(4 or 2, I am not sure is there a plane of symmetry here)


2,3-dichloropentane(2 or 4)


2,4-dichloropentane(obviously none for a plane of symmetry)



2,5-dichloropentane(2,4?)


But my surprisingly the answer says it's only 5. That's even lower than my lower estimate. I am not sure how there are 5 enantiomers.



Answer



2-chloropentane is optically active compound hence in some cases we will get only diastereomers. For example 1,2-dichloropentane is single product because it is formed by attack at carbon no. 1 hence no change in chirality of carbon no. 2. So product formed by attack at carbon 1 (one chiral product) carbon3 (two chiral product i.e. diastereomers) carbon 4 (one chiral product, i.e. one chiral and one meso) carbon5 (one chiral product)


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