Introduction to Reaction Mechanism and Kinetics with a Look at Acids and Bases Flashcards
Reaction Mechanisms
explain how molecules react to break or form new bonds, as a series of elemental (simple) steps.
Double-barbed arrows
Two electron movement
Nucleophile
An electron RICH species that reacts by donating an electron pair to an electron-poor species
Often has a lone pair
Electrophile
An electron-poor species (polarized bond or empty orbital) that reacts by accepting an electron pair from a nucleophile.
How do you determine if a molecule is an electrophile or nucleophile
Resonance
Which way to electrons move? (nuc. to elec. or vice versa)?
Electron pairs always move from nucleophile to electrophile
- are used to establish a bond
When a bond is broken where do the electrons go?
To the more electronegative atom
Polarizability
Ability to shift bonding or nonbonding electrons in response to nearby nucleophile or electrophile.
How to predict reaction mechanism
Reactions occur at or near functional groups and often involve polar bonds due to polarizability and differences in electronegativity
Between what can reactions occur?
Intermolecular (between 2 or more atoms)
Intramolecular (between 2 functional groups on the same molecule)
Which is more likely to be an electrophile, O or N?
Nucleophilic Behavior: Both oxygen and nitrogen can be nucleophilic, but nitrogen is usually a stronger nucleophile than oxygen because:
Nitrogen is less electronegative, so it holds onto its lone pair of electrons more loosely, making it more willing to donate electrons.
Oxygen, on the other hand, is more likely to be involved in electrophilic reactions (due to its electronegativity), especially in situations like carbonyl compounds or in esterification reactions.
Equilibrium
describes the extent of a reaction (how much product forms, if any)
K eq
Keq <1 = Reactants favored
Keq >1 = Products favored
Keq and ΔG equation
ΔG = -RTLnKeq
Keq and ΔG/Exergonic and Endergonic
Keq >1 and ΔG <0 = Products are favored so the reaction is exergonic
Keq <1 and ΔG >0 = reactants are favored and the reaction is endergonic
Bond Dissociation Energies (B.D.E.s)
Amount of energy required to symmetrically break a covalent bond
Total energy of bonds broken + total energy of bonds formed
Entropy
measure of freedom of movement or disorder\
ΔS more positive = more disorder = ΔG more negative
ΔS more negative= less disorder = ΔG more positive
Transition state
highest energy structure on an energy diagram
Intermediate (I)
Carbocation
Carbocation
A positively charged ion (cation) in which the positive charge is localized on a carbon atom. Carbocations are highly reactive intermediates in many organic reactions, particularly in mechanisms such as SN1 and E1 reactions.
On a graph, how do you know the speed of a reaction?
Higher barrier = slower reaction
The slowest elementary step = rate-determining step of the reaction
Delta g double dagger is the energy difference between initial reactants and…
the highest T.S
Catalyst
increase reaction rate without changing Delta G of the overall reaction
Is not consumed in the reaction
Activation energy is lowered by providing a new reaction mechanism
Bronsted Acid
Proton donor (H+)
Bronsted Base
Proton acceptor (H+)
pKa
Strength of acid
The lower the pKa value, the stronger the acid.
A weak conjugate base means the acid will be
strong
Electronegativity
Conjugate bases in which the atom carrying the negative charge is more electronegative and more stable (so is a weaker base).
High electronegativity = increased ability to accommodate negative charge.
Induction
Removal of electron density from an atom by a strongly electronegative atom nearby.
This increases the ability to accommodate negative charge and increases stability.
Hybridization
Orbitals with higher s’ character are lower in energy because s orbitals experience a greater effective nuclear charge.
Conjugate bases with unpaired electrons in orbitals with greater s’ character’ are more stable
Resonance
Charge delocalization increases the ability to accommodate negative charge and increases stability.
Lewis acid
electron pair acceptor
Lewis base
electron pair donor
