Isomers
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same formula but different chemical structure
isomers
isomers that share only molecular formula
structural isomers (constitutional)
isomers that share molecular formula and atom connectivity
stereoisomers
stereoisomers that differ in rotation around single (sigma) bonds
conformational isomer
stereoisomers that can be interconverted only by breaking bonds
configurational isomer
if mirror image cannot be superimposed on original object, has handedness (a left and a right side), no internal plane of symmetry
chiral
has mirror image that can be superimposed on original object
achiral
an asymmetric core of optical activity; e.g. a C atom with four different ligands
chiral center
formula representing possible number of stereoisomers
2^n (n = number of chiral centers)
molecules that are non-superimposable mirror images of each other, have same atom connectivity but opposite configurations at EVERY chiral center, identical chemical and physical properties except optical activity and reactions in chiral environments
enantiomers
molecules that are chiral and share same atom connectivity, but are not mirror images of each other, differ at SOME (but not all) of multiple chiral centers, have different chemical properties
diastereomers
refers to rotation of plane-polarized light by a chiral molecule, enantiomers rotate plane-polarized light at same angle but in opposite directions; d- or (+) = clockwise rotation, l- or (-) = counterclockwise rotation
optical activity
specific rotation ([α])
[α] = α(obs) / (c * l) where: α(obs) = observed rotation in degrees c = concentration in g/mL l = path length in dm
when (+) and (-) enantiomers are present in equal concentrations, rotations cancel out and no optical activity is observed
racemic mixture
diastereomers in which substituents differ in their position around an immovable bond, in simple compounds we use cis and trans, in more complicated molecules with polysubstituted double bonds (E) and (Z) are used; (Z) = zame zide, (E) = opposite sides
cis-trans isomers (geometric)
a molecule with chiral centers that has an internal plane of symmetry, not optically active
meso compound
spatial arrangement of atoms or groups in a stereoisomer
configuration
a chiral molecules’ configuration in relation to another chiral molecule
relative configuration
describes exact spatial arrangement of atoms or groups of a chiral molecule, independent of other molecules, R or S
absolute configuration
steps to assign R vs S
1) assign priority to ligands by atomic number (4 doesn’t matter) 2) arrange lowest priority substituent in back 3) draw a circle around molecule from highest to lowest priority (skip 4) 4) clockwise = R, counterclockwise = S
favored position of bulky groups on boat confirmation
equatorial (E)