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stereochemistry cheatsheet
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rhighs committed Oct 28, 2024
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| **Atropisomers** | No | Restricted rotation biaryls (substituted biphenyls) |
| **Configurational Isomers** | Depends | Encompasses both enantiomers and diastereoisomers |
| **Homomers** | Identical | Two ethanol molecules |


### Stereochemistry defs cheatsheet

| **Category** | **Term** | **Definition** | **Key Characteristics** |
|--------------------------|------------------------|--------------------------------------------------------------------------------------------------------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| **Molecular Symmetry** | **Chiral** | Molecule that cannot be superimposed on its mirror image. | - Has at least one stereogenic center<br> - No plane of symmetry<br> - Exists as two enantiomers (R and S forms) |
| | **Achiral** | Molecule that can be superimposed on its mirror image. | - Often has a plane of symmetry<br> - No stereogenic centers in most cases<br> - No enantiomers |
| | **Meso Compound** | Achiral molecule with stereogenic centers, has internal symmetry. | - Contains stereogenic centers<br> - Plane of symmetry makes it superimposable on its mirror image<br> - Optically inactive |
| **Types of Isomers** | **Structural Isomers** | Molecules with the same molecular formula but different connectivity. | - Different physical and chemical properties<br> - Examples: chain isomers, positional isomers |
| | **Stereoisomers** | Molecules with the same molecular formula and connectivity but different spatial arrangements. | - Includes enantiomers and diastereomers |
| | **Conformational Isomers** | Isomers that differ by rotation around single bonds. | - Examples: staggered and eclipsed ethane<br> - Same connectivity, flexible arrangement |
| | **Configurational Isomers** | Isomers that cannot be interconverted without breaking bonds. | - Includes enantiomers and diastereomers<br> - Require bond breaking to interconvert |
| **Types of Stereoisomers** | **Enantiomers** | Non-superimposable mirror-image molecules. | - Opposite configurations at all stereogenic centers<br> - Same physical properties (except optical rotation direction) |
| | **Diastereomers** | Stereoisomers that are not mirror images of each other. | - Different configurations at one or more (but not all) stereogenic centers<br> - Different physical and chemical properties |
| **Enantiomeric Properties** | **Optical Activity** | Ability of chiral molecules to rotate plane-polarized light. | - Clockwise rotation: (+) or dextrorotatory<br> - Counterclockwise rotation: (-) or levorotatory<br> - Racemic mixtures are optically inactive |
| | **Racemic Mixture** | 1:1 mixture of two enantiomers, optically inactive as rotations cancel. | - Forms racemate crystal structure in solids<br> - Often requires chiral resolution techniques to separate |
| **Stereochemical Rules** | **Cahn-Ingold-Prelog (CIP)** | System to assign priority to substituents on a stereocenter for R/S configurations. | - Priority based on atomic number, bond multiplicity, and connectivity<br> - Used to determine R (clockwise) or S (counterclockwise) configurations at stereogenic centers |
| | **R/S Configuration** | Labels to specify the absolute configuration of a chiral center. | - Assign priorities, arrange so the lowest priority is away, and trace from highest to lowest to determine R or S |
| | **E/Z Configuration** | Used to designate the configuration of double bonds (geometric isomerism). | - **E**: higher priority groups on opposite sides<br> - **Z**: higher priority groups on the same side |
| **Stereogenic Centers** | **Stereogenic Center** | Atom, usually carbon, with four different substituents, giving rise to chirality. | - Necessary for chirality<br> - Each stereogenic center can have R or S configuration |
| | **Prochiral Center** | Atom that can become chiral by changing one substituent. | - Important in reactions that introduce chirality<br> - Example: carbonyl carbon in prochiral ketones |
| **Stereochemistry in Reactions** | **Enantioselective** | Reaction that selectively produces one enantiomer over the other. | - Common in synthesis of chiral drugs<br> - Requires chiral catalysts or reagents |
| | **Diastereoselective** | Reaction that favors the formation of one diastereomer over others. | - Involves chiral centers but doesn’t create mirror images<br> - Used in complex molecule synthesis |
| | **Stereospecific** | Reaction where a specific stereoisomer of the reactant leads to a specific stereoisomer of the product. | - Examples: SN2 reactions that invert configuration<br> - Mechanism inherently linked to stereochemistry |

This table covers fundamental stereochemistry terms, making it a handy reference for understanding different isomer types, configurations, and stereochemical effects in reactions.

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