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Chirality

Chirality. “ chiral ”. Greek for hands. chiral =. non-superimposable mirror images. chiral =. no plane of symmetry. C *. C with 4 different substituents. stereocenter. chiral C. Chirality. H. H. *. HOH 2 C. C. CHO. OHC. C. CH 2 OH. OH. OH. enantiomers.

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Chirality

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  1. Chirality “chiral” Greek for hands chiral = non-superimposable mirror images chiral = no plane of symmetry C* C with 4 different substituents stereocenter chiral C

  2. Chirality H H * HOH2C C CHO OHC C CH2OH OH OH enantiomers non-superimposable mirror images no plane of symmetry

  3. H * HOH2C C CHO OH H OH C H O C H 3-D Representations glyceraldehyde 2,3-dihydroxy propanal CHO vertical = into paper * H OH horizontal = out of paper CH2OH

  4. CHO CHO H OH HO H CH2OH CH2OH * * (+)-glyceraldehyde (-)-glyceraldehyde * *

  5. identical in most properties Enantiomers differ in: 1.interaction with polarized light 2. interaction with chiral environments Light interacts with molecules when it passes through them [interaction of electrical fields] When light encounters mirror image of molecule, interaction is reversed

  6. Polarized light One enantiomer - rotate light to the left (-) Other enantiomer - rotate light to the right (+) in 50/50 mix - no net rotation racemic mixture one enantiomer - polarized light will be rotated optical activity

  7. Chirality 2. Enantiomers in chiral environments hands chiral mittens achiral - plane of symmetry achiral environments don’t distinguish between enantiomers gloves chiral - no plane of symmetry chiral environments do distinguish between enantiomers

  8. Chirality caraway seed enantiomers of carvone spearmint gum Is there a C* * Is there a plane of symmetry no carvone

  9. CH3 CH3 O O * C H2C CH3 C H3C CH2 Chirality * (+) carvone (-) carvone spearmint caraway rotates light to left rotates light to right racemic mixture - optically inactive taste buds are chiral environment

  10. Formation of chiral compounds catalyzed by chiral enzymes alkene + H2O alcohol fumerase chiral * + H2O fumaric acid optically inactive COOH * HO H Malic acid (+) CH2CO2H optically active

  11. carboxylic acid + alcohol ester + H2O O-CH3 * * + + H2O CH3OH (-) lactic acid methyl lactate (+) optically active optically active

  12. ketone mild reducing agent 2o alcohol + NaBH4 + * * HO H H OH pyruvic acid (-) lactic acid (+) lactic acid optically inactive optically active optically active racemic mixture inactive

  13. CHO HO H HO H CH2OH Compounds with more than 1 C* * * CHO * H OH * H OH CH2OH L-Erythrose D-Erythrose

  14. CHO H OH HO H CH2OH diastereomers CHO CHO H OH HO H H OH HO H CH2OH CH2OH L-Erythrose D-Erythrose 2 C* A maximum of 2n steroisomers * * * * enantiomers CHO HO H enantiomers H OH diastereomers: non-mirror image stereoisomers CH2OH L-Threose D-Threose

  15. 22 = 4 stereoisomers only 3 steroisomers H | H | | OH II CH2OH CH2OH CH2OH * HO * C * OH HO * OH * * OH HO CH2OH CH2OH CH2OH * * + LiAlH4 I III IV CH2OH * OH * HO CH2OH plane of symmetry I and II enantiomers III and IV meso compound optically active optically inactive

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