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ISOMERISM- part 2 STEREOISOMER & STEREOCHEMISTRY

ISOMERISM- part 2 STEREOISOMER & STEREOCHEMISTRY . Prepared by KH. SADIQUE FAISAL ASST.LECTURER DEPARTMENT OF PHARMACY, NUB. THE ORIGIN OF OPTICAL ACTIVITY . THE ORIGIN OF OPTICAL ACTIVITY . THE ORIGIN OF OPTICAL ACTIVITY . RACEMIC MIXTURE.

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ISOMERISM- part 2 STEREOISOMER & STEREOCHEMISTRY

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  1. ISOMERISM- part 2STEREOISOMER & STEREOCHEMISTRY Prepared by KH. SADIQUE FAISAL ASST.LECTURER DEPARTMENT OF PHARMACY, NUB

  2. THE ORIGIN OF OPTICAL ACTIVITY

  3. THE ORIGIN OF OPTICAL ACTIVITY

  4. THE ORIGIN OF OPTICAL ACTIVITY

  5. RACEMIC MIXTURE • An equimolar mixture of two enantiomers is called a racemic mixture (or racemate or racemic form). A racemic mixture causes no net rotation of plane-polarized light. • Figure 5.14 (a) A beam of plane-polarized light encounters a molecule of (R)-2-butanol, a chiral molecule. This encounter produces a slight rotation of the plane of polarization. (b) Exact cancellation of this rotation occurs if a molecule of (S)-2-butanol is encountered. (c) Net rotation of the plane of polarization occurs if (R)-2-butanol is present predominantly or exclusively.

  6. RACEMIC FORMS AND ENANTIOMERIC EXCESS • A sample of an optically active substance that consists of a single enantiomer is said to be enantiomerically pure or to have an enantiomeric excess of 100%. An enantiomerically pure sample of (S)-(+)-2-butanol shows a specific rotation of +13.52. • On the other hand, a sample of (S)-(+)-2-butanol that contains less than an equimolar amount of (R)-(-)-2-butanol will show a specific rotation that is less than +13.52 but greater than zero. Such a sample is said to have an enantiomeric excess less than 100%. • The enantiomeric excess (ee), also known as the optical purity, is defined as follows:

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