chiralityg

chiralityg - Stereochemistry 1 Copyright, Arizona State...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Stereochemistry 1 Copyright, Arizona State University Copyright, Arizona State University Chirality Molecular "Handedness" (more...) • Stereoisomers differ in orientation of atoms in space Example (seen already) Diastereomers C H H C Cl Cl C H Cl C Cl H + trans-diastereomer (no dipole) cis-diastereomer NON-Superimposable!! C H Cl C Cl H C H H C Cl Cl X X NON-Superimposable!! • DIASTEREOMERS have same molecular formula but different physical and chemical properties, they are different molecules. They are also NON-SUPERIMPOSABLE 1 Enantiomers • Important NEW type of stereoisomer is the ENANTIOMER • Enantiomers are "mirror image" stereoisomers • Enantiomers have the property of chirality • Chiral objects have a "handedness" W C X Y Z W C X Y Z mirror image not the same (non-superimposable) W C X Z Y not the same asymmetric (chiral) center (starred) * * * • The molecule on the left is the enantiomer of that on the right, they are enantiomers • Both isomers are chiral (they differ from their mirror image), in this case as a consequence of a "chiral center" • A chiral center is an atom with four different groups attached to it (starred above) • The presence of a chiral center (also known as an asymmetric center) is the most common reason for a molecule to be chiral Example : lactic acid (the chiral/asymmetric centers are starred) H C H 3 C OH CO 2 H H C CH 3 HO HO 2 C * * "R-lactic acid" "S-lactic acid" Example : 4-bromooctane CH 3 CH 2 CH 2 CH 2 –C–CH 2 CH 2 CH 3 H Br * small difference between these groups, still chiral! • switch any two substituents on a chiral center to get the enantiomer F C Br Cl H F C Br Cl H F C Br H Cl = switch enantiomers Stereochemistry 2 Copyright, Arizona State University Example : substituted cyclohexane Me Et Et Me * * * * Me Et Et Me * * * * enantiomers conformers conformers Et Me Et Me = = enantiomers 1.1 Specifying Configuration (Chirality); Cahn-Ingold-Prelog Notation • Specifies the "configuration" at each asymmetric or chiral/asymmetric center, equivalent to "cis-" and "trans-" • Same rules used to decide priority of the substituent groups as used iwhen determining Z and E in alkenes 1) Assign priorities to groups attached to chiral center according to atomic # 2) Compare 2nd, 3rd etc. atom from center as necessary, look for first point of difference 3). Multiple bonds "add up" 4) Determine direction of rotation 1 > 2 > 3 looking with #4 group pointing "away" Example H C H 3 C OH CO 2 H H C CH 3 HO HO 2 C * * 4 1 2 3 4 1 2 3 OH CO 2 H H 3 C look towards 4 1 2 3 HO HO 2 C CH 3 1 2 3 clockwise (R)-lactic acid anticlockwise (S)-lactic acid Example H C C C CH 3 C CH 3 H H H CH 3 H this group has priority 1 3 4 clockwise - (R) * this group has priority 2 H C C C CH 3 C CH 3 H H H CH 3 H * C, C, H attached C, C H attached H, H, and C attached (back to the previous carbon, C=C) H, H, H attached C C 2 1 • treat each double bond as an additional single bond to count the 3 atoms that are further connected to each...
View Full Document

This note was uploaded on 01/07/2012 for the course CHM 233 taught by Professor Skibo during the Fall '08 term at ASU.

Page1 / 13

chiralityg - Stereochemistry 1 Copyright, Arizona State...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online