Organic Chemistry Isomers

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Structural Isomers
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Also called constitutional isomer. The least similar of all isomers, only sharing their molecular formula
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Physical Properties
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Characteristics that don’t change the composition of the matter, including melting point, boiling point, solubility, odor, color, and density
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Chemical Properties
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Characters that have to do with the reactivity of the molecule with other molecules and result in changes in chemical composition
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Stereoisomers
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Isomers that have the same formula and the same connectivity, but differ in how the atoms are arranged in space. This group includes conformational and configurational isomers
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Conformational Isomers
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Isomers that are the same molecule, only at different points in their natural rotation around single bonds
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Newman Projection
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A depiction of a molecule in which it is visualized along a line extending through a carbon-carbon bond axis
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Staggered
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Conformation where there is minimal steric repulsion between electron clouds due to no overlapping of the atoms
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Anti
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Staggered conformation in which the largest groups are 180 degrees apart
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Gauche
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Staggered conformation in which the largest groups are 60 degrees apart
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Eclipsed
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Conformation in which the largest groups are 120 degrees apart and the atoms are overlapping
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Totally Eclipsed
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Conformation in which the largest groups have 0 degrees of separation. This is the highest energy state
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Ring Strain
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Strain that affects the stability of cycloalkanes based on angle strain, torsional strain, and nonbonded strain (steric)
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Angle Strain
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Strain that results when bond angles deviate from their ideal values by being stretched or compressed
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Torsional Strain
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Strain that results when cyclic molecules must assume conformations that have eclipsed or gauche interactions
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Nonbonded Strain
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(ven der Waals repulsion) Strain that results when nonadjacent atoms or groups compete for the same space
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Axial
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Perpendicular to the plane of the ring (sticking up or down)
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Equatorial
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Parallel to the plane of the ring (sticking out)
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Configurational Isomers
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Isomers that can only change from one form to another by breaking and reforming covalent bonds. Two categories include enantiomers and diastereomers
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Optical Isomers
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Isomers that affect the rotation of plane-polarized light. Enantiomers and diastereomers are examples of these
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Chiral
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Describes a molecule that’s mirror image cannot be superimposed on itself, due to lack of an internal plane of symmetry
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Achiral
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Describes a molecule that can be superimposed on itself and possesses a plane of symmetry
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Chiral Center
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A carbon that has four different substituents attached
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Enantiomers
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Chiral isomers that are nonsuperimposable mirror images of each other
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Diastereomers
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Chiral isomers that share the same connectivity but are not mirror images of each other
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Racemic Mixtures
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When both (+) and (-) enantiomers are present in equal concentrations
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Geometric Isomers
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Subtype of diastereomers in which substituents differ in their position around an immovable bond (double bond, ring structure, etc)
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Cis
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When two substituents are on the same side of an immovable bond
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Trans
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When two substituents are on opposite sides of an immovable bond
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Meso Compound
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A molecule with chiral centers that has an internal plane of symmetry
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Configuration
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Spatial arrangement of atoms or groups in a molecule
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Relative Configuration
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A chiral molecule’s configuration in relation to another chiral molecule. Used to determine which type of isomers two molecules are
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Absolute Conformation
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A chiral molecule’s exact spatial arrangement of atom or groups, independent of other molecules
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(E)
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When the two highest priority substituents are on opposite sides of a double bond
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(Z)
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When the two highest priority substituents are on the same side of a double bond
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(R)
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After groups are assigned priority in an asymmetric molecule, the arrow is clockwise
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(S)
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After groups are assigned priority in an asymmetric molecule, the arrow is counterclockwise
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Fischer Projection
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A way to represent three-dimensional molecules using horizontal lines (out of page) and vertical lines (into page). Point of intersection is carbon atom

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