Ch 3 Curved Arrow, Resonance, Acids/Bases, Chem Equilibrium Flashcards
Lewis Acid-Base Association
electron deficient compound (less than an octet): acid
electron donor (makes new bond): base
Curved arrow notation
movement of electrons
Electron-pair displacement reactions
electrons don’t always go to electron deficient molecules
*require two arrows - break into 3 particles
Nucleophile - likes nuclei so is negative (electron rich!)
- donates electrons: can come from a bond or from an electron pair
Electrophile - likes electrons so is positive (electron poor…)
Leaving group - group accepting electrons from breaking bond
*reversing a reaction reverses the roles
Resonance
electrons move
-more than two structures can be present
*DO NOT break or make single bonds
*include formal charges
*overall charge of each contributor must be the same
-hybrid structure is the most stable
Importanter Structures:
*complete octet resonance structures > electron deficiency
*neg charges on electronegative molecules and pos on less electronegative
*neutral structures > separated strutures
Bronsted Acids and Bases
acid: donates proton (not electron!)
base: accepts proton (a positive molecule: H+)
Reaction: electron-pair displacement reaction with proton as electrophilic center (a positive molecule being moved around)
Conjugate base: acid that lost a proton (accepted electrons)
Conjugate acid: base that gained a proton (donated electrons)
Amphoteric: compounds that can act as acid OR base; water! (watch in reaction to see what it acts as)
Equilibrium Constant
= products/reactants * concentrations
At Equilibrium -
K > 1: products favored
K < 1 : reactants favored
K = 1 : neither favored
Standard Free Energy (G)
K is related to difference in G between reactants and products
*lower G = more stable (favored at equilibrium)
*products favored in equilibrium (K > 1), then change in G is negative
-products are at lower energy
*reactants favored in equilibrium (K < 1), then change in G is positive
-products must have more energy
K and change in G
K > 1 G < 0
K < 1 G > 0
K = 1 G = 0
Bronsted Acids
Strength
-how well it transfers a proton to a Bronsted base
*Lewis and Bronsted are the same base and acid but wording has to change lots
Dissociation Constant (Ka)
how far a reaction will go in a direction
*strong acid = small pKa (big Ka)
*weak acid = big pKa (small Ka)
-log (Ka) = pKa
Autoionization of water: pKa = 14
Henderson Hasselbach
helps you figure out if a dissociation reaction is dominantly acid, base or mix
Stronger acids/bases
more reactive
(reactions progress because reactants want to be more stable)
Impacts on acidity
Charge effect: more positive molecules are more acidic
Element effect: more electronegative molecules are more acidic
Hybridization effect: tighter molecules are more acidic (triple bonds
Resonance effect: more resonance (more stable) = more acidic
Induction (polar effect): tighter molecule increases stability -> increases acidity; but electron donating groups destabilize the acid (becomes weaker)
