Analyzing Organic Reactions
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Lewis Definition of Acids and Bases
concerns with the transfer of electrons in the formation of coordinate covalent bonds
Bronsted - Lowry Definition of Acid and Bases
focuses on proton transfer
Lewis Acid
electron acceptor in the covalent bond tend to be electrophiles vacant p-orbitals to accept electrons with or stay as positively polarized atoms
Lewis Base
electron donor for the covalent bond nucleophiles lone pair of electrons to donate or they just carry negative charge
Coordinate Covalent Bonds
when both electrons in the bond come from the same staring atom (the lewis base)
Bronsted Lowry Acid
species that donates a proton (loses positiveness)
Bronsted Lowry Base
species that accepts a proton (loses negativeness)
Amphoteric
molecules that can act as either Bronsted Lowry Acid/Base like water as it can accept and donate H+ Al(OH)3 HCO3- , HSO4-
Ka
acid dissociation constant measures strength of an acid in solution Ka = ( [H+] [A-] )/ [HA] pka = - log Ka
More acidic molecules will have _____ pKa and more basic molecules will have ____ pKa
smaller , larger
Generally, bond strength ______ down the periodic table meaning that acidity ______ . Also the more electronegative an atom, the _____ the acidity. When these two trends oppose each other, ______ takes precedence.
decreases increases higher lower bond strength
Alpha Hydrogens
attatched to the alpha carbon of carbonyl carbons they are the acidic hydrogen’s easily lost as the -enol form of carbonyl carboanions are stabilized by resonance.
Functional Groups that act as acids are _______ . They are readily accepting lone pairs from ______ reactants Functional groups that act as bases are ______.
Alcohols Aldehyde/Ketone (alpha carbons) Carboxylic Acids Carboxylic Derivatives basic (nucleophilic) amines amides
Nucelophiles
contain lone pairs/pi bonds that can from new bonds with electrophiles good bases
Nucelophilic/Electrophilic strength is determined on _________ with a common electrophile. Thus they are a ______ property. This is different from bases as acids/bases depend on _____ of a reaction, so it is a ______ property
relative rates of reaction kinetic equilibrium position thermodynamic
Nucelophilicity is determined by 4 factors:
Charge: more electron density, the more nucleophilic it is Electronegativity: decreases as electronegativity increases as they are less likely to share electron density Steric Hindrance: bulkier molecules are less nucleophilic Solvent: protic solvents can hinder nucleophilicity by protonating nucleophile or forming H bonds
In POLAR PROTIC solvents, nucleophilicity increases _____ the periodic table. In POLAR APROTIC solvents, nucleophilicity increases _______ the periodic table.
going down going up
In protic solvents, nucleophilicity decreases in halogens like this: In aprotic solvents, nucleophilicty decreases in this order:
I - > Br- > Cl - > F- F > Cl > Br > I as no protons can get in the way and nucleophilicty depends on basicity HI forms a strong acid so its less likely to form bonds with H HF is a weak acid and will easily form bonds with H
Electrophiles
electron accepting species with a positive charge or polarized atom that will accept an electron pair always act as acids nature of leaving group influences electrophilicty of of species
A greater deal of positive charge increases electrophilicity, so a carbocation is _____ electrophilic than a carbonyl carbon.
more
Carboxlyic derivatives are ranked by electrophilicity from most reactive to least
Anhydrides, Carboxylic Acids, Esters, Amides
Leaving Groups
molecular fragments that retain electrons after heterolysis
Heterolytic Reactions
opposite of coordinate covalent bonds a bond is broken and bothe electrons are given to one of the two products best one stabilize the extra electrons weak bases are more stable and make good leaving groups can be augmented by resonance and inductive events
SN1 Reaction
1) the rate limiting step where leaving group leaves and a carbocation is made 2) Nucleophile then attacks the carbocation resulting in the substitution product racemic mixture is made as it passes through a planar intermediate and the nucleophile can attack from either side