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Answer the following: Where: R_1 notequalto R_2 notequalto R_3 notequalto X notequalto = + 13.5 degree product with [] = In the above reaction, optically active compound I has a specific rotation of +13.5 degree, and compound II with a 100% exists with a specific rotation of + degree or -16.8 degree. However, when compound II was prepared from I the specific rotation of the product was a) Explain this observation in terms of the mechanism of the reaction. (Show the reaction Mechanism) b) Calculate the of the product c) What is the percent composition of the product.
Expert Answer
a) Drawn below is the Sn1 mechanism of the reaction. First step of formation of stable tertiary carbocation intermediate. Now depending upon the steric bulk of R1, R2 and R3, the resultant ratio of inverted or retention of product stereochemistry will be seen.
b) enantiomeric excess = -6.72 x 100/-16.8 = 40%
So the enantiomer with -6.72 degree rotation is in 70% and the enantiomer of it is in 30% ratio in the product isolated.
c) Percent composition of product = 70 : 30
