organic exam 2
meso compounds
-have chiral centers -overall molecule is achiral -have internal plane of symmetry -not optically active --> don't rotate plane polarized light -each chiral center rotates light in opposite directions so overall the rotations cancel out
# of configurational isomers=
2^n n=# of stereocenters
nonsuperimposable
when mirror images of organic molecules cannot be completely matched
chiral
A molecule or carbon atom bonded to four different groups and without a plane of symmetry; thus, it is not superimposable upon its mirror image and has an enantiomer. no double bonds
anti conformation
A type of staggered conformation in which the two largest groups are antiperiplanar to each other; the most energetically favorable conformation
sterioisomer
Compounds with the same structural formula but with a different arrangement of the atoms in space.
conformational isomers
Stereoisomers that differ by rotation about one or more single bonds, usually represented using Newman projections.
torsional strain
Strain associated with adjacent bonds getting too close
steric strain
Strain associated with atoms "bumping" into each other
angle strain
Strain associated with improper bond angles
Two molecules that have the same molecular formula and connectivity but are nonsuperimposable mirror images of each other are related by being labeled as __________.
enantiomers
half-chair conformation
The unstable conformation halfway between the chair conformation and the boat conformation. Part of the ring is flat in the half-chair conformation.
gauche conformation
a conformation with a 60 degree dihedral angle between the largest groups
twist boat conformation
a nonplanar conformation of a cyclohexane ring that is twisted from and slightly more stable than a boat conformation
ring strain
arise from angle strain, torsional strian and nonbonded strain; multiplying strain by each CH2 group
A molecule and its chair flip are related by being labeled as __________.
conformational isomers
An eclipsed and a staggered Newman projection are related by being labeled as __________.
conformational isomers
constitutional isomers
differ in the order of attachment of atoms
Two molecules are not mirror images of each other. However, rotating the single bonds of one of the molecules such that it becomes a nonsuperimposable mirror image of the other molecule creates __________.
enantiomers
superimposable
identical in all respects. the three-dimensional positions of all atoms coincide when the molecules are placed on top of each other.
Cyclobutane adopts a nonplanar structure called the puckered conformation. Why does cyclobutane adopt the puckered conformation rather than a planar structure?
less torsional strain
chair conformation
most stable conformation of cyclohexane
envelope conformation (cyclopentane)
nonplanar; strain is minimized
pseudorotation
occurs by partial rotations about the C-C bond
constitutional isomers
same molecular formula, different connectivity
dihedral angle
the angle created by two intersecting planes
Newman projection
the nearer atom is depicted as a point, the further atom is depicted as a circle