exam 2: Ch 4 & 14 Flashcards
polycyclic ring systems
classified by the number of rings they contain
named by how many bond disconnections to make a linear structure (bicyclic, tricylic)
fused ring systems
share a bond
bridged ring system
connected at 2 nonadjacent atoms
spirocyclic ring system
share a single C atom
heteroaromatic rings
aromatic rings that include 1+ heteroatom
have resonance structures, incorporating lone pair on heteroatom
newman projections
toward = right side
chair conformations
up C have up axial H and down equatorial H
ring flip: axial becomes equatorial, but up stays up
stable when most and largest groups are equatorial
up = wedge
fischer projections
horizontal = wedge/towards
vertical = dashed/away
orient so C chain is vertical with lowest numbered C at the top
chiral C/stereoisomer
C with 4 different groups
not part of a multiple bond
if in a ring, different path in both directions
plane of symmetry
if present, achiral
cuts through molecule such that one half is the mirror of the other
number of stereoisomers
2^# of stereocenters
Cahn Ingold Prelog Rules
rank atoms bound to stereocenter according to atomic number, highest first
orient molecule so lowest priority is facing away
draw arrow 1 through 3
clockwise: R
counterclockwise: S
enantiomer
kind of stereoisomer
chiral molecule
opposite chirality at all stereoisomers
diastereomers
stereoisomer that is not a mirror image
draw by changing chirality of some of the stereocenters
cis and trans are diastereomers
meso compound
achiral molecule with chirality centers
mirror image is identical to itself, no enantiomer
contain at least 2 chiral centers and a plane of symmetry
physical properties
enantiomers have the same physical properties, except optical purity
optical purity/activity
ability to rotate plain polarized light
substance must be chiral and one enantiomer must be in excess
(specific rotation of sample)/(specific rotation of pure enantiomer)
enantiomeric ratio (er)
%major enantiomer : %minor enantiomer
enantiomeric excess (ee)
%major enantiomer - %minor enantiomer
0 when it’s 50/50 (racemic mixture)
100 when there’s a single enantiomer (enantiopure)
IR spectroscopy
vibration of a bond is related to strength
good for identifying functional groups
Hooke’s Law
frequency is directly related to force constant and indirectly related to mass
force constant (k)
stiffness = bond strength
increase bond strength, increase frequency
influenced by hybridization, resonance, nearby EN
reduced mass (m1 and m2)
mass of either side of the bond
decrease mass, increase frequency
hybridization and frequency
more s character (sp) increases k, which increases frequency
resonance and frequency
reduces double bond character, decreases k, which decreases frequency
nearby EN and frequency
pulls e-, reducing contribution from a single bond resonance form, increases k and frequency