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

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Presentation transcript:

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

Chirality C H HOH 2 CCHO OH * COHC H OH CH 2 OH enantiomersnon-superimposable mirror images no plane of symmetry

3-D Representations glyceraldehyde propanal2,3-dihydroxy vertical = into paper CHO horizontal = out of paper * OHH CH 2 OH C H HOH 2 CCHO OH * O C H OH C H

* * * CHO OHH CH 2 OH * CHO HOH CH 2 OH 1. Most oxidized C on top OH on left = L enantiomer D-(+)-glyceraldehyde L-(-)-glyceraldehyde 2. C * furthest from top OH on right = D enantiomer

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

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

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

Chirality * (-) carvone (+) carvone spearmintcaraway rotates light to left rotates light to right racemic mixture - optically inactive taste buds are chiral environment CH 3 O C H3CH3CCH 2 * CH 3 O C H2CH2C

Formation of chiral compounds catalyzed by chiral enzymes alkene + H 2 O alcohol + H 2 O optically inactive fumerase chiral * COOH CH 2 CO 2 H HOH Malic acid L-L- optically active fumaric acid *

carboxylic acid + alcoholester + H 2 O lactic acid D-(-)- * optically active + CH 3 OH O-CH 3 + H 2 O * methyl D-(+)- optically active lactate

ketone + mild reducing agent2 o alcohol + NaBH 4 OH H HOH pyruvic acid optically inactive ** D-lactic acidL-lactic acid optically active racemic mixture inactive

Compounds with more than 1 C * ** CHO CH 2 OH OH H H D-Erythrose CHO CH 2 OH HO H H L-Erythrose * *

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

+ LiAlH 4 | | | C H OH H ** 2 2 = 4 stereoisomers I CH 2 OH * * OH HO II CH 2 OH * * OH HO enantiomersI and II optically active III CH 2 OH * * OH IV CH 2 OH * * HO plane of symmetry III and IVmeso compound optically inactive only 3 steroisomers

** 2 2 = 4 stereoisomers COOH OH HOH H COOH H HOH HO enantiomers COOH OH H H H COOH HHO plane of symmetry I II I and II IIIIV III and IV meso compound superimposible mirror images same optically active optically inactive