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C.I. 3.6

C.I. 3.6. Optical Isomerism. Types of isomerism. Isomerism. Structural isomerism. Stereoisomerism. Geometric isomerism. Optical isomerism. Different compounds- different properties. geometric isomerism. Optical Isomerism.

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C.I. 3.6

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  1. C.I. 3.6 Optical Isomerism

  2. Types of isomerism Isomerism Structural isomerism Stereoisomerism Geometric isomerism Optical isomerism

  3. Different compounds- different properties. geometric isomerism

  4. Optical Isomerism Arises because of the different ways you can arrange four different groups around a carbon atom. Hang on!! Aren’t -amino acids a group of compounds that have four different groups around a carbon atom?

  5. four groups of electrons around the central atom • four bonding pairs • TETRAHEDRAL shape • bond angle exactly 109

  6. alanine imaginary mirrors

  7. All molecules have mirror images – however they don’t all exist as two isomers. What makes an isomer is the fact that the mirror image and the original molecule are non-superimposable! The only way to make these two superimpose is to break & reform bonds.

  8. Left and right hands are an example of non-superimposable mirror images.

  9. Enantiomers ? • Molecules such as alanine that exist in these two forms = optical isomers or enantiomers. • We distinguish between the two enantiomers of a molecule by +/-, D/L or more correctly R/S. • A 50/50 mixture of the two enantiomers is called a racemic mixture or a racemate.

  10. Some more key words … • Molecules that are not superimposable on their mirror images are called chiral molecules. • A carbon surrounded by 4 different groups is called a chiral centre. chiral centre of alanine

  11. The CORNy rules for naming enantiomers. Optical isomers exist as L-enantiomers or D-enantiomers. L-enantiomer D-enantiomer R R CO CO N N

  12. The CORNy rules for naming enantiomers. • Imagine looking down on the molecule with the single H atom point straight up towards you. • Label the other three groups • COOH = CO • R-group = R • NH2 = N • If CORN is arranged in a CLOCKWISE direction it is the L-amino acid. • If CORN is arranged ANTI-CLOCKWISE it is a D-amino acid.

  13. How do enantiomers differ? • Behave identically in ordinary test-tube chemical reactions. • Have same physical properties. BUT!! • Behave differently in presence of other chiral molecules. • e.g. Taste-buds are ‘chiral’ D-amino acids taste sweet, L-amino acids are tasteless or bitter.

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