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Single isomer versus racemate: is there a difference? Clinical comparisons in allergy and gastroenterology
David A Flockhart1, Harold S Nelson
1Department of Clinical pharmacology, Indiana University School of Medicine, Indianapolis, Indiana, USA.
Abstract:
Many commonly prescribed drugs exist as a mixture of two distinct chiral isomer forms (enantiomers), each with its own unique chemistry, receptor affinity, and pharmacokinetic profile. Much is unknown concerning the clinical utility of these single enantiomers. This review of the stereoisomers of two commonly used drugs--albuterol for asthma and omeprazole for gastroesophageal reflux disease (GERD) and peptic ulcers--examines the improved efficacy, pharmacokinetics, decreased adverse effects, and fewer drug-drug interactions associated with single enantiomers.
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SN1 Reaction: Stereochemistry
In the first step of an SN1 reaction, the bond between the electrophilic carbon and the leaving group ionizes to generate the carbocation intermediate. The second step of the mechanism is the nucleophilic attack.
In the formed carbocation, the positively charged carbon is sp2 hybridized with a trigonal planar geometry. As all the three substituents lie on the same plane, a plane of symmetry for the...

