if a compound contains no pi bonds and no rings, will have 2n+2 hydrogen atoms
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)
the stabilization of reaction intermediates by sharing of electrons through sigma bonds
pull electrons toward themselves through sigma bonds, can stabilize e- rich regions
push electron density away from themselves through sigma bonds, can stabilize e- deficient regions
stabilize charge by delocalization through pi bonds
contains three or more atoms that each bear a p orbital and are aligned parallel to one another, creating the possibility of delocalized electrons
electrons that are confined to one orbital; either a bonding orbital between atoms or a lone pair orbital
electrons that can interact with orbitals on adjacent atoms
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
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)
a measure of how strong a nucleophile is, or how easily it can donate an e- pair
what are some trends in nucleophilicity?
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.
electron-deficient species that often have a positive charge and an incomplete octet. “electron-loving”
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
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)
compounds that have the same molecular formula but different connectivity
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?
what conformation has the absolute minimum potential energy?
in the chair conformation, why do larger groups prefer to be in the equatorial axis?
to reduce 1,3-diaxial interactions
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)
any molecule that cannot be superimposed on its mirror image
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
R/S configuration assigned to chiral centres
absolute configuration R
absolute configuration S
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
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
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
a 50/50 mixture
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 (+)/(-)?
if n is the number of chiral centres, how do you determine the number of possible stereoisomers?
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)
a sub-class of diastereomers that differ in their absolute configuration at a single chiral centre
epimers that form as a result of ring closure
anomeric centre/anomeric carbon
the carbon/chiral centre that distinguishes the two anomers
hydroxyl group is down
hydroxyl group is up
have chiral centres but are not optically active (achiral) because there is an internal plane of symmetry
diastereomers that differ in orientation of substituents around a ring or a double bond (constrained by geometry and cannot rotate freely, fixed configuration)
two longer alkyl chains are on the same side of the molecule
two longer alkyl chains are on opposite sides of the molecule
higher priority groups are on the same side of the double bond
higher priority groups are on opposite sides of the double bond