When one or more shape is possible, it is determined by the number and position of the lone
pairs of electrons.
Instantaneous Dipole Moment - answer✔✔Exists in an otherwise nonpolar molecule. Occurs
because the electrons in a bond move about the orbital and at any moment may not be distributed
exactly between the two bonding atoms, even when the atoms are identical.
London Dispersion Forces - answer✔✔Occur between two instantaneous dipoles; the weakest
dipole-dipole force (vs. hydrogen bonds which are the strongest dipole-dipole forces).
Zwitterion - answer✔✔A neutral molecule with a positive and negative electrical charge at
different locations within the molecule at a pH of 7.
Ex: amino acids -> amine group deprotonates the carboxylic acid group.
Isomers - answer✔✔Molecules that have the same molecular formula but are different
compounds.
Conformational Isomers (Conformers) - answer✔✔Not true isomers - different spatial
orientations of the same molecule. At low temperatures, the anti-conformation is the most
common.
Structural Isomers - answer✔✔Have the same molecular formula but different bond-to-bond
connectivity; simplest form of isomer.
Stereoisomers - answer✔✔Two molecules with the same molecular formula and same bond-to-
bond connectivity that are not the same compound. Like conformational isomers but contain at
least one *chiral/stereo center (C bonded to 4 different substituents).
2 types:
- Enantiomers
- Diastereomers
Enantiomers - answer✔✔Stereoisomers that have opposite absolute configurations at EACH
chiral center (mirror images). Cannot be separated by physical means.
When in equal concentrations -> racemic mix.
Resolution = the separation of enantiomers.
Same physical and chemical characteristics except in 2 cases:
1) Reactions with other chiral compounds.
2) Reactions with polarized light.
Diastereomers - answer✔✔Stereoisomers that are not mirror images (are not the same
compound). Can be separated by physical means (crystallization).
Geometric isomer: special type of diastereomer, have different physical properties.
- Cis: has dipole moment -> strong intermolecular forces so has high boiling point; lower
symmetry does not form crystals as easily so has lower melting point; has steric hindrance so has
higher heats of combustion.
- Trans: no dipole moment - lower boiling point, higher melting point, lower heats of
combustion.
--> better to use E (Opposite) and Z (same)
Epimer - answer✔✔Diastereomers that differ at only one chiral center.
Anomers - answer✔✔Two diastereomers formed from a ring closure at an epimeric C.
Anomeric carbon: the chiral carbon of the anomer.
Ex: glucose - anomeric C determines if it's α-glucose or β-glucose.
Meso Compounds - answer✔✔Optically inactive (achiral) molecule with two chiral centers;
have a plane of symmetry between their centers which divides the molecule into halves that are
mirror images of each other.
Absolute Configuration - answer✔✔The only way to absolutely describe a chiral molecule.
R = rectus: right (clockwise)
S = sinister: left (counterclockwise)
*for when H (or any other 4th priority substituent) is on DASHES.
Mirror images of chiral molecules always have opposite absolute configurations.
*Note: retention of configuration does not mean that absolute configuration is retained; it means
that there is no inversion.
# stereoisomers of a chiral molecule = 2^n where n = # of chiral Cs
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