1-review Flashcards
formal charge formula
(group #) – (# of bonds) – (# of non-bonded electrons)
what are exceptions to the octet rule (2)
- incomplete octets common for first-row elements`
- expanded octets: common for elements with d orbitals
definition of electronegativity
ability of an atom to attract shared electrons in a bond towards itself from the surrounding atoms
what are bond dipoles
polarization of the bond
de Broglie regarding movement of electrons
the electrons’ movement can be described by mathematical equations (waves’ equations)
schrödinger regarding movement of electrons
this movement is related to a series of energy levels (solutions to waves’ equations)
heisenberg and Born regarding movement of electrons
the exact position of an electron cannot be determined (probability region)
probability of finding electrons in nodes
probability of finding electrons on the top and bottom nodes of the p orbital is the same, in the middle is 0
vsepr theory of electrons
to determine three-dimensional distribution of electrons around atoms.
valence bond model
probability of finding the shared spin-paired electrons is confined to the regions between the atoms (localized bonds).
definition of hybrid orbitals:
result from mixing atomic orbitals s and p to give a sp type of orbital.
hybridization sp3
1 s orbital, 3 p orbitals, tetrahedral, SN = 4
hybridization sp2
1 s orbital, 2 p orbitals, trigonal planar, SN = 3
hybridization sp
1 s orbital, 1 p orbital, linear, SN = 2
in what type of orbitals do lone pairs reside
As for the lone pairs, the ones that contribute to the resonance and by that were delocalized into an adjacent bond will be in 2p orbitals and the one that didn’t will reside in a sp2 orbital. otherwise it’s just matches the main atom that it’s on
what is resonance
concept developed to explain the structures that can’t be explained by simple Lewis structures. electrons are delocalized (shared) between multiple atoms via p orbitals. resonance hybrids are the true structures
how many arrows with empty orbitals (resonance)
only show one arrow per resonance form
how many arrows with excess orbitals (resonance)
show two arrows per resonance form
list the three resonance contributors
- incomplete octet (it becomes the minor contributor right away)
- charge (which one has lowest charge, becomes major contributor)
- electronegativity (more EN atom, it will accommodate charge better)
list of 5 things to look for in major resonance form
- The most atoms with complete octets.
- fewest number of formal charges
- The most covalent bonds
- negative charges on most electronegative atoms and positive charges on least electronegative atoms
- charge separation: like charges have max separation and unlike charges have min separation
list of 4 things to look for in minor resonance form
- The most atoms with the least filled octets
- Resonance contributors in which there is a greater separation of charge
- A resonance structure with a lower number of total bonds
- Negative charge is located on the less electronegative atom
what are atomic orbitals
formed by an electron cloud around an atom, it is the region having the highest probability of finding an electron in an atom
what are molecular orbitals
formed by a combination of atomic orbitals, it is the region having the highest probability of finding an electron in a molecule. the number of molecular orbitals formed is equal to the sum of atomic orbitals combined.
what are the two possibilities of overlapping
- in-phase overlap: bonding (sigma, pi)
- out-out-phase overlap: anti bonding (sigma, pi)
sigma bond
direct (head on) overlap
pi bond
indirect (side by side) overlap
homo
highest occupied molecular orbital. for nucleophiles, the HOMO is where electrons are given
lumo
lowest unoccupied molecular orbital, for electrophiles, the LUMO is where the electrons are received
what are conformations?
rotation around single bonds (staggered, eclipsed, gauche, and antiperiplanar)
acyclic molecules are illustrated how?
conformations illustrated by Newman projections
cyclic molecules allieviate their strain how?
adopting chair conformations
what are newmann projections
standardized method of representation of conformations around a single bond for acyclic structure
what is antiperiplanar
conformation in which the two angle between two groups of atoms is between 150º and 180º
what happens during a chair flip
axial hydrogens rotate to equatorial positions, equatorial hydrogens rotate to axial positions
what most stable conformation?
equatorial because of less 1.3 diaxial interactions
chiral molecules have what characteristic
no internal symmetry
achiral molecules have what characteristic
in the presence of a plane of symmetry
what is superimposable
able to be superimposed so as to align with another exactly and show no perceptible difference
what are enantiomers
mirror image non-superposable
stereogenic center
carbon with four different substituents (asymmetric carbon)
cahn-Ingold Prelog priorities and configurations
look at the stereocenter axis with the atom with the lowest priority in the back then verify the order of priority of the other 3 groups
- if it is counterclockwise then its S
- if it is clockwises then its R
- if the small group is in the front: rotate the molecule 120º or invert structure
what are configurations
the spatial arrangement of the bonds of the groups attached to a stereogenic center (fixed bonds) AND OR changing connectivity and spatial arrangement leading to stereoisomers
diastereomer
stereoisomers that are not enantiomer (changing the configuration of some of the stereocenters)
what is cis
when substituent bonds are oriented in the same direction
what is trans
when the substituent bonds are oriented in opposing directions
higher pKa
more basic
lower pKa
more acidic
henderson-hasselbalch equation
pH= pKa + log (A-)/(HA)
- pH < pKa -> HA major
- pH - pKa -> 50% of both
- pH > pKa -> A- major
how to predict the course of a reaction? (2 steps)
1- identify the most acidic and the most basic atom using these 2 methods
(- compare the values of pKa of acidic protons
- compare the relative stability of the 2 molecules or their conjugates)
2- determine the direction of the equilibrium:
- the equilibrium favours the side of the most stable compounds (weak acid and weak base)
list 5 things that are qualitative prediction of equilibria
- electronegativity
- atom size
- hybridization
- resonance (charge delocalization)
- induction
prediction of equilibria- 1) electronegativity
in the same row, the more electronegative atom has the ability to better accommodate negative charge
- stronger acid has a weak conjugate base (the base has a negative charge on the more electronegative atom)
- weaker acid had a strong conjugate base (the base has a negative charge on the less electronegative atom)
prediction of equilibria- 2) atomic size
in the same group, the acidity increases with the size of the atom. larger atom accommodates better the negative charge
- stronger acid has a weak conjugate base (the base has a negative charge on the larger atom)
- weaker acid has a strong conjugate base (the base has a negative charge on the smaller atom)
prediction of equilibria- 3) hybridization:
since s orbitals lower in energy than p, greater s character leads to greater stability. sp (50%) > sp2 (33%) > sp3 (25%)
prediction of equilibria- 4) charge delocalization- resonance
(by resonance) the delocalisation of the negative charge by resonance stabilizes the charge (charge distributed over multiple atoms)
- double bond adjacent to a charge makes delocalization possible
prediction of equilibria- 5) induction
when the substituents are more electronegative, there is better accommodation of the negative charge. the inductive effect decreases with distance.
lewis acid
acceptor of the pair of electrons
lewis base
donor of the pair of electrons
requirements for aromaticity (4 things)
- be cyclic
- have a p orbital on all participating ring atoms
- be planar
- have (4n+2)π electrons delocalizing in the ring (with n an integer; Hückel’s rule)
requirements for anti aromaticity (4 things)
- be cyclic
- have a p orbitial on all participating ring atoms
- be planar
- have (4n)π electrons delocalizing in the ring (with n an integer)
requirements for non-aromaticity (3 things)
- be cyclic
- have at least one sp3 atom as part of the ring
- be non-planar
