Resumen de Using NMR To Probe the Regio- and Stereochemistry of the Hydration of 1-Hexene
Shahrokh Saba, Donald D. Clarke, Christa Iwanoski, Thomas Lobasso
This undergraduate organic laboratory experiment complements previously described and popular experiments on hydration of 1-hexene where students experimentally establish the Markovnikov regioselectivity of alkene hydration. In this experiment, students explore not only the regiochemistry but also the stereochemistry of 1-hexene hydration and obtain spectral evidence that hydration of 1-hexene yields 2- and 3-hexanols as major products and that these chiral alcohols are obtained as racemic mixtures. This objective is achieved by converting commercial samples of racemic 2- and 3-hexanols to diastereomeric camphorsulfonate esters using commercial samples of enantiomerically pure (1S)-(+)-10-camphorsulfonyl chloride. The product directly obtained from hydration of 1-hexene is also esterified using the same reagent. 1H and 13C NMR spectra of the products from each reaction are then obtained, analyzed, and compared. Thus, students determine the composition of the diastereomeric mixtures. The results lead to a postlab discussion of NMR spectroscopic analysis of enantiomers and diastereomers, stereochemical relationships between faces of planar species such as carbocations, and the effect of a chiral auxiliary on a racemate. Most importantly, students experimentally prove one of the main doctrines of organic stereochemistry whereby racemates are always produced from reactions of achiral starting materials that afford chiral products.
