saturated
if a compound contains no pi bonds and no rings, will have 2n+2 hydrogen atoms
unsaturated
a compounds has at least one pi bond or a ring, will have fewer than 2n+2 hydrogen atoms
degree of unsaturation (d)
(2n+2-x)/2 (x is the number of hydrogens and any monovalent atoms, oxygen has no effect, replace each N with 1 C and 1 H)
inductive effects
the stabilization of reaction intermediates by sharing of electrons through sigma bonds
electron-withdrawing groups
pull electrons toward themselves through sigma bonds, can stabilize e- rich regions
electron-donating groups
push electron density away from themselves through sigma bonds, can stabilize e- deficient regions
resonance effects
stabilize charge by delocalization through pi bonds
conjugated system
contains three or more atoms that each bear a p orbital and are aligned parallel to one another, creating the possibility of delocalized electrons
localized
electrons that are confined to one orbital; either a bonding orbital between atoms or a lone pair orbital
delocalized
electrons that can interact with orbitals on adjacent atoms
resonance hybrid
the average of all resonance contributors
strength of an acid refers to:
the degree to which it dissociates (or donates its proton) in solution
the strength of the acid is determined by:
the extent to which the negative charge on the conjugate base is stabilized
nucleophiles
species that have unshared pairs of electrons or pi bonds and, frequently, a negative charge. “nucleus-loving”
nucleophiles are also known as:
Lewis bases (electron-pair donators)
nucleophilicity
a measure of how strong a nucleophile is, or how easily it can donate an e- pair
what are some trends in nucleophilicity?
CARIO
polarizability
how easy it is for the electrons surrounding an atom to be distorted, larger atoms are generally more polarizable and thus more nucleophilic. generally apply down columns in the periodic table.
electrophile
electron-deficient species that often have a positive charge and an incomplete octet. “electron-loving”
electrophilicity
a measure of how strong an electrophile is, or how well it can accept an electron pair
electrophiles are also known as:
Lewis acids (electron-pair acceptors)
what determines a good leaving group?
they are more likely to dissociate from their substrate because they are more stable in solution. Ex. weak bases, large atoms, less charged/uncharged
ring strain
arises when bond angles between ring atoms deviate from the ideal angle predicted by the hybridization of the atoms. the strain weakens carbon-carbon bonds and increases reactivity
what are conditions required for hydrogenation reactions?
heat (120 degrees Celsius), H2, Ni, a ring structure with ring strain (ex. cyclopropane, cyclobutane)
constitutional isomers
compounds that have the same molecular formula but different connectivity
conformational isomers
compounds that have the same molecular formula and connectivity, but differ from on another by rotation about a sigma bond (ex. staggered vs. eclipsed)
which conformation (staggered, eclipsed) is more stable and why?
staggered is more stable because it has less electronic repulsion and less steric hindrance
what conformation has the absolute maximum potential energy?
syn conformation
what conformation has the absolute minimum potential energy?
anti conformation
in the chair conformation, why do larger groups prefer to be in the equatorial axis?
to reduce 1,3-diaxial interactions
stereoisomers
molecules that have the same molecular formula and connectivity but differ in the spatial arrangement of the atoms (cannot be interconverted by rotation about sigma bonds)
chiral
any molecule that cannot be superimposed on its mirror image
achiral
a molecule that can be superimposed on its mirror image, has a plane of symmetry
stereocenter/stereogenic centre/asymmetric centre
a carbon atom that is a chiral centre and attached to four different groups
absolute configuration
R/S configuration assigned to chiral centres
absolute configuration R
clockwise
absolute configuration S
counter-clockwise
enantiomers
non-superimposable mirror images, can occur when chiral centres are present
what are some properties of enantiomers?
will always have opposite absolute configurations, will have many identical physical properties, opposite rotation of plane-polarized light (optical activity)
what is an important property that differs between enantiomers?
the manner in which they interact with plane-polarized light
optically active
a compounds that rotates the plane of polarized light
dextrorotatory (d), (+)
a compound that rotates plane-polarized light clockwise
levorotatory (l), (-)
a compound that rotates plane-polarized light counterclockwise
specific rotation
the magnitude of rotation of plane-polarized light for any compound
what does specific rotation depend on?
the structure of the molecule, the concentration of the sample, the path length through which the light must travel
a pair of enantiomers will rotate plane-polarized light with:
equal magnitude but opposite directions
racemic mixture
a 50/50 mixture
racemate
a racemic mixture of enantiomers
what is a property of a racemate/racemic mixture of enantiomers?
it is not optically active
is there a relationship between configuration (R/S, alpha/beta) and optical activity (+)/(-)?
NO
if n is the number of chiral centres, how do you determine the number of possible stereoisomers?
2^n
diastereomer
stereoisomers that are non-superimposable, non-mirror images
what are some of the properties between diastereomers?
different physical and chemical properties, no predictable relationship between the specific rotations of diastereomers
how do you separate enantiomers (lab process)?
RESOLUTION (use an enantiomerically pure chiral probe that associates with the components of the mixture through either covalent bonds or intermolecular forces to create diastereomers with different physical properties, allows for separation by filtration, work-up step generates the isolated enantiomerically pure product)
epimers
a sub-class of diastereomers that differ in their absolute configuration at a single chiral centre
anomer
epimers that form as a result of ring closure
anomeric centre/anomeric carbon
the carbon/chiral centre that distinguishes the two anomers
alpha configuration
hydroxyl group is down
beta configuration
hydroxyl group is up
meso compound
have chiral centres but are not optically active (achiral) because there is an internal plane of symmetry
geometric isomers
diastereomers that differ in orientation of substituents around a ring or a double bond (constrained by geometry and cannot rotate freely, fixed configuration)
cis configuration
two longer alkyl chains are on the same side of the molecule
trans configuration
two longer alkyl chains are on opposite sides of the molecule
(Z) configuration
higher priority groups are on the same side of the double bond
(E) configuration
higher priority groups are on opposite sides of the double bond
