Stereochemical aspects
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This document discusses various aspects of stereochemistry. It begins by explaining Fischer's D and L notation system for assigning configurations based on a compound's relation to glyceraldehyde. It then discusses pseudo asymmetric centers in meso compounds and cis-trans isomerism that can occur due to restricted bond rotation around double bonds. Finally, it introduces the E-Z system for naming geometric isomers with three or more different groups, which is based on Cahn-Ingold-Prelog priority rules to determine whether higher priority groups are on the same or opposite sides of the double bond.
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L 8 geometric-isomerism_pch217_2013_2014
1. The document discusses geometric isomerism in cyclic compounds and alkenes. Geometric isomers occur when restricted rotation around double bonds results in fixed positions of groups on the same or opposite sides.
2. It introduces the cis/trans system for naming geometric isomers as well as the E/Z system which is used when there are three or more different groups around a double bond.
3. The document also discusses conformations in open-chain compounds, which can rotate freely around sigma bonds and exist as staggered or eclipsed conformers.
Stereochemistry
The document discusses various topics in stereochemistry including:
1. Stereochemistry deals with the three dimensional structure of molecules and how it affects properties.
2. Isomers can be classified as structural, positional, functional, ring-chain, metamers, and tautomeric depending on their structure.
3. Chiral molecules have "handedness" and lack a plane of symmetry, allowing the existence of enantiomers which are non-superimposable mirror images. Systems like R/S, D/L, and E/Z are used to describe chiral molecule stereochemistry.
Stereochemistry(s.r.y.)
The document discusses different types of isomers and stereochemistry. It begins by defining constitutional isomers as compounds with the same molecular formula but different connectivity of atoms. Stereoisomers are described as having the same molecular formula and connectivity but different three-dimensional orientations of atoms. The two main types of stereoiosmers are discussed as enantiomers, which are non-superimposable mirror images, and diastereomers, which are not mirror images. Various examples of geometric isomers, optical isomers and assigning stereochemistry are also provided.
Absolute & relative configuration
1. Relative configuration compares the arrangement of atoms in space of one compound to another, while absolute configuration precisely describes the arrangement of atoms in space.
2. Cahn-Ingold-Prelog rules were developed in the 1950s to determine absolute configuration, assigning R or S based on the atomic priorities and spatial arrangement of groups around chiral carbons.
3. To determine absolute configuration using Cahn-Ingold-Prelog rules, groups attached to a chiral carbon are ranked by priority and the molecule is oriented such that the lowest priority group is in the back. Clockwise arrangement is labeled R and counterclockwise is S.
Optical activity in helicines
The document discusses helicity and chirality in organic chemistry. It explains that helicity arises in molecules with a helical shape, which are inherently chiral. It also describes how overcrowding in molecules like helicenes can lead to helicity. The document then discusses asymmetric synthesis and how existing chiral centers induce asymmetric induction to form diastereomers in unequal amounts. It presents Cram's rule and Prelog's rule as methods to predict the configuration of the predominant diastereomer based on the existing chiral centers.
Bp401tt fmf rnjrkNEW STEREOCHEMISTRY .pdf
This document discusses stereochemistry and optical isomerism. It defines stereochemistry as the detailed study of the three dimensional structure of organic compounds. Isomers can be constitutional/structural isomers or stereoisomers. Stereoisomers differ in the spatial arrangement of atoms but have the same connectivity. Optical isomers are stereoisomers that are non-superimposable mirror images called enantiomers. For a molecule to exhibit optical activity, it must lack symmetry elements like a plane of symmetry and have a chiral center. The R-S system and CIP rules are used to assign configuration of chiral centers.
Steriochemistry ppt
This document provides an outline and overview of stereochemistry concepts including isomerism, chiral and achiral carbons, enantiomers, diastereomers, geometric isomerism, asymmetric synthesis, and optical resolution methods. Key topics covered are classification of isomers, properties of chiral carbons, differences between enantiomers and diastereomers, cis-trans isomers in cyclic compounds, how asymmetric synthesis produces unequal product amounts, and methods for separating enantiomers including mechanical, biochemical and chemical separation. Applications of stereochemistry in medicinal compounds and biological systems are also briefly discussed.
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Stereochemical aspects
- 1. STEREOCHEMICAL ASPECTS PREPARED BY- MOHAMAD HAIDER ROLL NO.- 04/MPH/DIPSAR/19 DEPARTMENT OF PHARMACEUTICAL CHEMISTRY, DIPSAR
- 2. CONTENTS Fischer’s D and L notation Pseudo asymmetric centers Cis-Trans isomerism E-Z system
- 3. Fischer’s D and L notation The D-L system corresponds to the configuration of the molecule: spatial arrangement of its atoms around the chirality center. D-L system tells us about the relative configuration of the molecule, compared to the enantiomers of glyceraldehyde as the standard compound.
- 4. Compounds with the same relative configuration as (+)-glyceraldehyde are assigned the D prefix, and those with the relative configuration of (-)-glyceradehyde are given the L prefix. It only relates the stereochemistry of the compound with that of glyceraldehyde, but says nothing about its optical activity.
- 5. In assigning the D and L configurations of sugars, we could directly look for the OH group of the bottom asymmetric carbon in the Fischer projection. If it's located on the right, we designate it with D, and vice versa.
- 6. Pseudo Asymmetric Centers A pseudo asymmetric centre is found in a meso molecule (a molecule with multiple stereocenters that is superimpossible on its mirror image) where a plane of symmetry runs through a streogenic centre and that stereogenic centre’s two substituents are constitutionally the same but configurationally different.
- 7. Example: 1. Other examples:
- 8. Cis-Trans Isomerism Cis-trans isomerism (also known as geometric isomerism) is a form of stereoisomerism. These isomers occur where there is restricted rotation somewhere in a molecule, generally in carbon-carbon double bond. Cis isomer is an isomer where two of the same atoms are on the same side of the double bond in a molecule.
- 9. A trans isomer consists of molecule with two same atoms but here the atoms lie in the opposite side of the double bond. Example: Cis-2-butene has both methyl groups on the same side of the molecule. Trans-2-butene has the methyl groups on opposite sides of the molecule. Their structural formulas are as follows:
- 10. There are two requirements: 1. Rotation must be restricted. 2. There must be two nonidentical groups on each doubly bonded carbon. When there is free rotation about the C–C bond, the two models represent exactly the same molecule; they are not isomers. Two structural formulas that look different can be drawn, but because of possibility of this free rotation about single bonds, these two structures represent the same molecule:
- 11. The presence of a double bond does not necessarily lead to cis-trans isomerism as shown:
- 12. E-Z System The traditional system for naming the geometric isomers of an alkene is to name them as cis or trans. But if there are three different groups (or four), then the cis/trans approach is insufficient to describe the different isomers. For such alkenes E-Z system is use. It is based on the same set of ‘Priority rules’ on which the R-S is based. These priority rules are often called the Cahn-Ingold- Prelog (CIP) rules.
- 13. The general strategy of the E-Z system is to analyze the two groups at each end of the double bond. At each end, rank the two groups using the CIP priority rules. Then, see whether the higher priority group at one end of the double bond and the higher priority group at the other end of the double bond. If they are on the same side it will be Z isomer (Z, from German zusammen = together) and on opposite sides, E isomer (E, from German entgegen = opposite).
- 14. • In simple cases, such as 2-butene, Z corresponds to cis and E to trans. However, that is not a rule as indicated in the following example:
- 15. THANK YOU