Question

An optically pure sample of R-C6H5CHClCH3 with a specific rotation of -190 was converterted into the corresponding alcohol via SN1 reaction. The specific rotation of optically pure R-C6H5CHOHCH3 is -42.3 What is the specific rotation of the product? The answer is NOT -42.3 Please Explain why, because I am lost

Answer 1

An optically pure sample of R-C6H5CHClCH3 with a specific rotation of -190 was converterted into the corresponding alcohol via SN1 reaction. So the product of the SN1 reaction reaction will be a raceimic mixture containg both  R-C6H5CHOHCH3 and  S-C6H5CHOHCH3.
R-C6H5CHClCH3 ------------->  R-C6H5CHOHCH3 + S-C6H5CHOHCH3. (SN1)

The specific rotation of optically pure R-C6H5CHOHCH3 is -42.3
So, the specific rotation of optically pure S-C6H5CHOHCH3 will be +42.3.

Hence, the specific rotation of the product i.e raceimic mixture will be zero (0).