University:
York University
Course:
CHEM 1000 | Chemical Structure
Academic year:

2021
Views:

110

Pages:

4
Author:

Niklas

Lecture 8 (02/04/21) Stereogenic element? Is a center, axis, or plane that is a Focus of Stereoisomerism, such that an interchange of two groups attached to the feature leads to Stereoisomers. Br H \ / C=C / \ H Br Alkene is Stereogenic Two Stereoisomers Br H \ / C=C / \ H Br Br Br \ / C=C / \ H H Alkene is Non-Stereogenic No Stereoisomers Molecules with > 1 chiral center 2,4-dihydroxy pentane HO-C-H-C-OH | | H H Max # Stereoisomers = 2^(# chiral centers) Assign Priority Based on groups Prioritize Based on MASS If tie, 1st pt. of diff. When you flip, what's R becomes S & vice versa. Absolute Configuration Chirality is a property of an object. R/S isomers have chiral centers. Molecule has chiral centers, but a plane of sym = "meso" Diastereomers: any stereoisomer of a given molecule that is not its enantiomer. Physical Properties of Enantiomers/Diastereomers Enantiomers: SAME: Identical physical properties: mp, bp, H/C NMR spectra Difficult to physically separate Different: Rotate plane polarized light Can interact with proteins differently Diastereomers: Different: mp, bp, H/C NMR spectra More easily separated Ex: polyols - alkanes w/ mult. -OH groups n = 4 max # isomers = 16 HO-OH-OH-OH 1 2 3 4 HO-OH-OH-OH 1 2 3 4 Enantiomers: All Flipped HO-OH-OH-OH 1 2 3 4 HO-OH-OH-OH 1 2 3 4 Diastereomers: 2 Flipped HO-OH-OH-OH 1 2 3 4 HO-OH-OH-OH 1 2 3 4 Diastereomers: 2 Flipped HO-OH-OH-OH 1 2 3 4 How to Spot Chiral Molecules: Lowest level of symmetry Cannot have plane of symmetry or inversion center OH | C---C | | OH OH Achiral OH | C---C | | OH OH Chiral Centers of Inversion: Ph = H / \ C C / \ / \ H C C H / \ / \ C C C H \ / \ / C C \ / H Phenyl Group X-Truxillic Acid: HO | HO-C-C-C-Ph | | Ph OH 4 Chiral Centers BUT ACHIRAL CREAM of TARTAR: (salt) potassium bitartrate Found in lees of wine (crystals on bottom of bottle & good wine) Biot (1832) - Rotated plane polarized light Pasteur (1847) - Sodium ammonium tartrate Diff. crystals (rotated light in opp. direction) HO-C-H | HO-C-H | COOH HO-C-H | HO-C-H | COOH HO-C-H | HO-C-H | COOH Tartaric Acid Stereoisomers