a student carries out a reduction of acetophenone, and uses IR and GC to determi

Question

a student carries out a reduction of acetophenone, and uses IR and GC to determine that 1-phenylethanol was successfully produced A student carries out a reduction of acetophenone, and uses IR and GC to determine that 1-phenylethanol was successfully produced. From a sample consisting of 0.524 g of the reaction product in 10.0 mL of ethanol, an optical rotation of +2.24 is observed. (S-1-phenylethanol has a specific rotation of -45°. Was the (R or (S isomer of 1-phenylethanol produced? In what enantiomeric excess? Show your calculations and explain your answer. reducing agent 1-phenylethanol acetophenone

Explanation / Answer

since the optical roration of the 1-phenylethanol was found to be + 2.24 a, provided (S)-1-phenylethanol has a

specific rotaion of -45 degrees. this means that (R)-1-phenylethanol has a specific rotaion of +55 degrees.

let the mole fraction of S isomer be xS and the R isomer be xR ...we got a resulting optical roration of +2.24 this

means

2.24 = xS (-45) + xR (+55)

since we know that xR + xS =1 ,

or,

2.24 = xS (-45) + (1- xS )(+55)

or xS = 0.5276 , simeq0.53 this means xR = 0.47

ee % of Rsimeq 47 %

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