Question

Briefly describe how you will interpret your NMR spectra to determine whether you have made the meso compound (R,S) or the chiral compounds (mixture of R,R and S,S).

Answer 1

The meso compound has a plan of symmetry that devides the molecule in two equal halves. As a result the carbons and hydrogen toms of two equivalent halves will become chemically equivalent. So the number of 13C and 1H peaks in NMR will be half of the number of carbons and hydrogens in the molecule. In an R,R or S,S compound there will be slight diffrence in the environment of hydrogen atoms. Hence the peaks corrsponding to the hydrogen atoms could be observed. Further thr R,R and S,S isomers may be subjectd to chiral derivitization and recording NMR of derivatives. However this is not possible in meso compounds, because meso compounds are achiral and chiral deivtzation can not be done.