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Organic Chemistry Ch. 2 - Isomers
MCAT
16
Organic Chemistry
Undergraduate 2
05/30/2016

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Term
structural isomers
Definition
aka constitutional isomers - same molecular formula but doesn't have to have same bonding or chemical or physical properties
Term
stereoisomers
Definition
share the same structural backbone but differ in how the atoms are arranged in space
Term
conformational isomers
Definition
differ by rotation around a single (σ) bond
Term
configurational isomers
Definition
can only be interchanged by breaking and reforming bonds; E/Z molecules are configurational
Term
What are the types of conformations in Newman projections?
Definition
  • staggered - no overlap of atoms; there is anti (two largest group are on opposite sides) and gauche (two largest groups are 60o apart; right next to each other but not on top)
  • eclipsed - two largest groups are 120o apart and overlap with smaller groups
  • totally eclipsed - 0o separation between two largest groups; least energetically favorable
Term
What are the factors that cause ring strain?
Definition
  • angle strain - created by stretching or compressing angles from their normal size
  • torsional strain - from eclipsing conformations
  • nonbonded strain - from interactions between substituents attached to nonadjacent carbons
Term
axial
Definition
atoms coming off of cyclohexane that stick up or down from the plane
Term
equatorial
Definition
those atoms on cyclohexane that stick out (are parallel) to the plane of cyclohexane; larger group goes in equatorial position
Term
enantiomer
Definition
two molecules that are nonsuperimposable mirror images; they differ in rotation at every chiral carbon
Term
diastereomers
Definition
chiral molecules that differ at some but not all of their multiple chiral centers
Term

How is a compound named if it rotates light clockwise?

counterclockwise?

Definition

dextrorotatory (d) and (+)

levorotatory (l) and (-)

Term
racemic mixture
Definition
has equal concetrations of two enantiomers, will not be optically active because the two enantiomers' rotations cancel each other other
Term
meso compounds
Definition
compound with an internal plane of symmetry, will be optically inactive because the two sides of the molecule cancel each other out; planes of symmetry can be through chiral carbons or between them
Term
determining S and R
Definition
number the atoms bonded to the carbon by highest to lowest priority; if the lowest priority group isn't at the back switch it with the group at the back; make a circle from highest to lowest priority, if it is clockwise then the molecule is R, counterclockwise S; if you had to switch the lowest priority group to the back then flip the configuration
Term
determining configuration Fischer projections
Definition
  • number the constituents bound to the carbon and determine R or S
  • if the lowest priority group is pointing to the side, and thus out of the page, flip the configuration
Term
What are the placement rules for substituents on cyclohexane in a chair conformation?
Definition

cis-1,2; cis-1,4  axial-equatorial

cis-1,3  equatorial-equatorial

trans-1,2; trans-1,4  equatorial-equatorial

trans-1,3  axial-equatorial

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