Chirality “chiral” Greek for hands chiral =

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Presentation transcript:

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

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

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

Enantiomers identical in most properties 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

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

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

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

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

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

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

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

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

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

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