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MCAT Org. Chem Ch. 2

QuestionAnswer
Structural isomers Isomers that share only a molecular formula and have different physical and chemical properties.
Conformational Isomers Isomers that differ by rotation around a single (sigmal) bond
Staggered Conformations Conformations that have groups 60 degrees apart, as seen in a Newman projection
Anti-staggered Confirmations Conformations in which the two largest groups are 180 degrees apart, and strain is minimized.
Gauche Staggered Molecules Molecules whose two largest groups are 60 degrees apart.
Eclipsed Conformations Conformations that have groups directly in front of each other, as seen in a Newman projection.
Totally Eclipsed Conformations Conformations whose two largest groups are directly in front of each other, so that strain is maximized.
Angle Strain Strain created by stretching or compressing angles from their normal size in cyclic molecules.
Torsional Strain Strain that results from eclipsing conformations
Nonbonded Strain Strain that results from interactions between substituents attached to nonadjacent carbons.
Note About Cyclic Molecules Minimizing Strain Cyclic molecules usually adopt nonplanar shapes to minimize angle strain
Axial Substituents Substituents that are attached to cyclohexane that are sticking up or down from the plane of the molecule. Axial substituents create more nonbonded strain.
Equatorial Substituents Substituents that are attached to cyclohexane that are sticking up or down from the plane of the molecule.
Note About Cyclohexane Molecules With Multiple Substituents The largest substituent will usually take the equatorial position to minimize strain.
Configurational Isomers Isomers that can only be interchanged by breaking and reforming bonds
Enantiomers Nonsuperimposable mirror images that have opposite stereochemistry at every chiral carbon. They have the same chem. and phys. properties except for rotation of plane-polarized light and reactions in a chiral environment.
Optical Activity The ability of a molecule to rotate plane-polarized light. d- or (+) molecules that rotate light to the right. I- or (-) molecules rotate light to the left.
Racemic Mixtures They have equal concentrations of two enantiomers, and will not be opitcally active because the two enantiomers' rotations cancel each other out.
Meso Compounds Compounds that have an internal plane of symmetry and will be optically inactive because the two sides of the molecule cancel each other out.
Disastereomers Non-mirror image stereoisomers that differ at some but not all chiral centers. They also have different chemical and physical properties.
Cis-trans Isomers A subtype of disastomers in which groups differ in position about an immovable bond. ex: double bond, or in a cycloalkane.
Chiral Centers Have four different groups attached to the central carbon.
Relative Configuration Gives the stereochemistry of a compound in comparison to another molecule.
Absolute Configuration Gives the stereochemistry of a compound without having to compare to other molecules.
Cahn-Ingold-Prelog priority rules Rules for absolute configuration in which priority is given by looking at the atoms connected to the chiral carbon or double-bonded carbons. Whichever has the highest atomic number gets the highest priority.
Note About Tie For Cahn-Ingold-Prelog Priority Rules If a tie exists, move outward from the chiral carbon or double-bonded carbon until the tie is broken.
Z Value For Alkene This occurs if the alkene has its highest-priority substituents are on the same side of the double bond
E Value For Alkene This occurs if the alkene has its highest-priority substituents are on opposite sides of the double bond.
Note On How To Determine A Stereocenter's Configuration Put the lowest priority group in the back and draw a circle from group 1 to 2 to 3 in descending priority.
R Stereocenter Configuration This occurs if the circle made for determining priority is clockwise.
S Stereocenter Configuration This occurs if the circle made for determining priority is counterclockwise.
Fischer Diagram Diagrams that have vertical lines that go into the page, which are shown by DASHES, and have horizontal lines that come out of the plane out of the page, which are shown by WEDGES.
Note About Switching One Pair Of Substituents In A Fischer Diagram This inverts the stereochemistry of the chiral center.
Note About Switching Two Pairs Of Substituents In A Fischer Diagram This makes the stereochemistry stay the same.
Note About Rotating A Fischer Diagram 90 degrees This inverts the stereochemistry of the chiral center. Rotating 180 degrees retains the stereochemistry.
Eq. 2.1: Specific Rotation [alpha] = alphaobs / c x l. [alpha] = specific rotation in degrees. alphaobs = observed rotation in degrees. c = conc. in g/mL. l = path length in dm (decameters)
Created by: SamB91