Chirality - University Of Illinois

Chirality - University Of Illinois

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 * HOH2C C CHO OH H OHC C CH2OH OH enantiomers non-superimposable mirror images no plane of symmetry 3-D Representations glyceraldehyde 2,3-dihydroxypropanal

O H H * C HOH C C CHO OH 2C H OH H CHO H * OH vertical = into paper horizontal = out of paper CH2OH * * (+)-glyceraldehyde (-)-glyceraldehyde

CHO H * CHO OH CH2OH HO * H CH2OH 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 dont distinguish between enantiomers gloves chiral - no plane of symmetry chiral environments do distinguish between enantiomers Chirality CH3 O H3C enantiomers of carvone Is there a C* *

C caraway seed spearmint gum CH2 carvone Is there a plane of symmetry no Chirality CH3 CH3 O H3C O * * C C

CH2 (-) carvone spearmint rotates light to left H2C CH3 (+) carvone caraway 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 + H2O chiral

* fumaric acid COOH optically inactive HO * H CH2CO2H (+) Malic acid optically active carboxylic acid + alcohol ester + H2O O-CH3 * + CH3OH (-) lactic acid optically active

* + H2O (+) methyl lactate optically active ketone + mild reducing agent + NaBH4 pyruvic acid optically inactive H * OH 2o alcohol HO * H (-) lactic acid (+) lactic acid optically active optically active racemic mixture inactive

Compounds with more than 1 C* H H H O H C C* C* C H HO OH OH CHO CHO H * OH HO H H * OH HO H

CH2OH D-Erythrose CH2OH L-Erythrose CHO H * OH H * OH CH2OH D-Erythrose CHO HO H

H OH CH2OH D-Threose 2 C* A maximum of 2n steroisomers enantiomers rs e m o e r e t s a i d enantiomers diastereomers: non-mirror image stereoisomers CHO HO

* H HO * H CH2OH L-Erythrose CHO H HO OH H CH2OH L-Threose 22 = 4 stereoisomers H H H C C C

HO OH OH I CH2OH * HO OH H H H H O | * * H C C C C C H | H HO OH OH OH O H II HO * CH2OH

+ LiAlH4 CH2OH * * OH CH2OH | H C only 3 steroisomers III CH2OH IV CH2OH * OH HO

* * OH HO * CH2OH CH2OH plane of symmetry I and II enantiomers III and IV meso compound optically active optically inactive

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