Ch. 4: Analyzing Organic Reactions Flashcards
Lewis acids
Electron acceptors; have vacant orbitals or positively polarized atoms
Lewis bases
Electron donors; they have a lone pair of electrons and are often anions
Brosnsted-Lowry acids
Proton donors
Bronsted-Lowry bases
Proton acceptors
Amphoteric molecules
act as either acids or bases, depending on reaction conditions (ex: water)
Acid dissociation constant: Ka
Measure of acidity, equilibrium constant corresponding to the dissociation of an acid, HA, into a proton (H+) and its conjugate base (A-). pKa is the negative log of Ka. a lower or negative pKa indicates a stronger acid. pKa decreases down the periodic table and increases w electronegativity
Common acidic functional groups
Alcohols, aldehydes, ketones, carboxylic acids and carboxylic acid derivatives. 𝞪-hydrogens (hydrogens connected to a 𝞪-carbon, a carbon adjacent to a carbonyl) are acidic
Common basic functional groups
Amines and amides
Nucleophiles
Nucleus loving, contain lone pairs or pi bonds. They have increased electron density and often carry a negative charge
Nucleophilicity
Similar to basicity; however, nucleophilicity is a kinetic property, while basicity is thermodynamic. Charge, electronegativity, steric hindrance, and the solvent can all affect nucleophilicity. Amino groups are common organic nucleophiles
Electrophiles
Electron loving and contain a positive charge or are positively polarized. More positive compounds are more electrophilic. Alcohols, aldehydes, ketones, carboxylic acids, and their derivatives can act as electrophiles.
Leaving Groups
The molecular fragments that retain the electrons after heterolysis. The best leaving groups can stabilize additional charge through resonance or induction. Weak bases make good leaving groups. Alkanes and hydrogen ions are almost never leaving groups bc they form reactive anions
Unimolecular nucleophilic substitution (SNI) reactions
Proceed in 2 steps: 1. The leaving group leaves forming a carbocation, an ion with a positively charged carbon atom. 2. The nucleophile attacks the planar carbocation from either side, leading to a racemic mixture of products. SNI reactions prefer more substituted carbons bc the alkyl groups can donate electron density and stabilize the positive charge of the carbocation. The rate of a SNI reaction dependent only on the concentration of the substrate: rate = k[R-L]
Bimolecular nucleophilic substitution SN2 reactions
Proceed in one concerted step. Nucleophile attacks at the same time as the leaving group leaves. The nucleophile must perform a backside attack, which leads to an inversion of stereochemistry. The absolute configuration is changed– (R) to (S) and vice versa– if the incoming nucleophile and the leaving group have the same priority in the molecule. SN2 reactions prefer less substituted carbons bc the alkyl groups create steric hindrance and inhibit the nucelophoe from accessing the electrophilic substrate carbon. The rate of an SN2 reaction is dependent on the concentrations of both the substrate and the nucleophile: rate = k[Nu:][R-L]
Oxidation state
Charge it would have if all of its bonds were ionic
