Structural Effect On Acidity and Basicity Flashcards
Hydrogen
Acid
Lone-pair
Base
A substance capable of acting as either an acid or base is called
Amphiprotic
Measure of the tendency of a compound to lose a proton
Acidity
Measure of a compound’s affinity for a proton
Basicity
The stronger the —–, the —— its conjugate base
Acid and Base Strengtg
Ka and pKa
Common Strong Acids include Six Monoprotic Acids
HCl, HBr, HI, HNO3, HClO3 and HClO4
Strong Bases include Hydroxides of the Alkali Metals and Alkaline Earth Metals
NaOH, KOH
(Ca(OH)2, Sr(OH)2, Ba (OH)2
Strong Acids and Base ionize —- in water
Completely
Weak Acids and Base ionize —— in Water
Partially
Acid
Electron pair acceptor
Base
Electron pair donor (donates)
Lewis Acids
Electrophiles (electron pair acceptor)
Lewis bases
Nucleophiles (electron pair donor
Electronegativity
Stabilize the negative charge of the conjugate base
Hybridization
Affects Electronegativity
Size
Size of the atom is more importanr than its electronegativity in determining acid strength
Inductive Effect
Shift in Electron density through charge polarization transmitted through sigma bonds
Electron withdrawing inductive effect
Stabilizing
Electron donating inductive effect
Destabilizing
Steric Effect
-Results from the presence of bulky groups.
-Results to congestion and twisting of bonds.
PI Electron Delocalization/Resonance
Delocalization of charge in the conjugate base anion increases acidity
Inductive Effect due to hybridization —— acidity
Resonance —— acidity
Increases
Weakens
Ortho position
Meta position
Para position
-steric effect>resonance effect
-inductive effect
-resonance effect
Structural Effects on Basicity
-The more stable the base, the less likely it is to be protonated
-The less stable the base, the stronger the base
Intermolecular Forces
Attractive forces between molecules
-Categorized into dipole-dipole forces, london dispersion forces and hydrogen bonding forces
Electrostatic
All intermolecular interactions are electrostatic, involving attractions between + and - species
Intramolecular force
Forces that hold atoms in a molecule (chemical bonds)
-Categorized into covalent, ionic and metal bonds
Van der Waals forces
3 types
London
Debye
Keesom
London dispersion force
dipole-induced dipole interaction
-weakest
-present in all substances
-significant only when molecules are close together
Keesom Force
Dipole-dipole interaction
-present in polar compounds
-stronger than London dispersion force
Hydrogen Bonding
-Strong type of dipole-dipole interaction
-Depends on the electronegativity of atom interacting with hydrogen
Ion-Dipole Interaction
Depends on ionic charge and polarity
Solubility
-Extent to which a substance is soluble
-mass of solute per volume of solvent
Like dissolves like
Solubility Rule
Dielectric Constant
-Related to polarity
-measure of the ability of the solvent to separate ionic charges
High dielectric constant =
Polar solvent
Low dielectric Constant =
Nonpolar solvent
Water as solvent
-dielectric constant of 80
- H bonds (polar)
Ether as Solvent
Dielectric constant of 4.3
-London dispersion forces (nonpolar)
Melting Point
-temperature at which a substance’s solid form is converted into liquid
Boiling Point
Temperature at which a substance’s liquid form is converted into gas
Ionic compounds
Higher MP because of ionic bonding
Covalent Compounds
Lower MP/BP because of London dispersion and H-bonding only
Reaction Equation
Describes what happens in a chemical reaction
Reaction Mechanism
-a detailed step by step description of how a chemical reaction occurs
-involve the movement of electrons
-allows one to preduct the likely outcome of a reaction
Ionic Reactions
Heterolytic cleavage
Heterolytic cleavage
Assymetrical cleavage of a bond
Radical reactions
Homolytic Cleavage
Radical
Homolytic Cleavage
Symmetrical cleavage of a bond
Radical
High energy species carrying an unpaired electron
Nucleophiles (Nu-, Nu:)
Electron rich, nucleus seeking reagents
-typically have a negative charge (anions), lone pair, or multiple bonds
Electrophiles (E+)
-electron defficient, electron seeking reagents
- have a + charge (cations), or are polarizable molecules that can develop an electron defficient center
Leaving Group (L-, L:)
-ions or neutral molecules that are displaced from a reactant as part of a mechanistic sequence
-displacement when a nucleophole attacks an electrophile that carries a suitable leaving group
Dependencd of the reaction rate on the concentration of reagents and other variables indicates the —— and —— of the molecules involved in the rate-determining step
Number
Nature
Molecularity
Number of reactant molecules involved in the rate determining step
-usually equivalent to the kinetic reaction order
Intermediate and Transition States
Transition State
Intermediate State
Transition State
Cannot be isolated, or even detected
-energy maximum
Intermediate
Stable and can be isolated
-Energy minimum
Types of Organic Reactions
Substitution
Elimination
Addition
Rearrangement
Radical Reactions
Types of Isomers
-Constitutional Isomer (Functional, Positional, Skeletal)
- Stereoisomers (Configurational, Conformational)
Arrhenius Acids and Bases
Concept is based om whether yields H+ or OH- in aqueous solution
Arrhenius Acid
Prodice hydrogen or hydronium ions in aqueous solution
Arrhenius Base
Produce hydroxide ion in aqueous solution
Bronsted Lowry Acid
Proton donor
Bronsted lowry base
Proton acceptor
Lewis Acid
Electron pair acceptor
Lewis base
Electron pair donor
Dipole-dipole Interaction
Keesom Force
Dipole-induced dipole interaction
London Disoersion Force
