



British Pharmacopedia 1988 gives specific optical rotation of (S)-Naproxen as 63.0° to 68.5°, when measured at 4% w/v in UV grade chloroform. As we had no UV grade chloroform, I measured the extracted freebase in UV grade DCM to get a specific optical rotation of 63.9°. I therefore declared my naproxen from 'DollarTree' to be the pure S enantiomer. This was quite preferable to the R enantiomer, which is said to be a liver toxin.