Organic Chemistry Ch 4. Analyzing Organic Reactions Flashcards
Lewis acids
Electron acceptors, have vacant orbitals or positively polarized atoms
Lewis bases
Electron donors, have a lone pair of electrons and are often anions
Bronsted-Lowry acids
Proton donors
Bronsted-Lowry abses
Proton acceptors
Amphoteric molecules
Can act as either acids or bases depending on reaction conditions, water is a common example
Acid dissociation constant
Ka - measure of acidity, it is the equilibrium constant corresponding to the dissociation of an acid, HA, into a proton and its conjugate base (A-)
pKa
The negative logarithm of Ka, a lower (or negative) pKa indicates a strong acid, decreases down the periodic table and increases with electronegativity
Common acidic functional groups
Alcohols, aldehydes, ketones, carboxylic acids, and carboxylic acid derivatives
alpha hydrogens
Hydrogens connected to an alpha carbon, are acidic
alpha carbon
Carbon adjacent to a carbonyl carbon
Common basic functional groups
Amines and amides
Nucleophiles
Nucleus loving and contain lone pairs or pi bonds, they have increased electron density and often carry a negative charge, kinetic property, can be impacted by charge, electronegativity, steric hindrance, and the solvent, common nucleophiles are amino groups
Electrophiles
Electron loving and contain a positive charge or are positively polarized, common electrophiles include alcohols, aldehydes, kenos, carboxylic acids, and their derivatives
Leaving groups
The molecules fragments that retain the electrons after heterolysis, the best groups can stabilize additional charge through resonance or induction, weak bases (or conjugate bases of strong acids) are also good leaving groups, alkanes or hydrogen ions almost never leaving groups because they form reactive anions
Sn1 reaction
Unimolecular nucleophilic substitution, rate depends only on the concentration of substrate, prefer more substituted carbons because the alkyl groups can donate electron density and stabilize the positive charge of the carbocation
1) the leaving group leaves, forming a carbocation
2) the nucleophile attacks the planar carbocation from either side, leading to a racemic mixture of products
Carbocation
An ion with a positively charged carbon atom
Sn2 reaction
Bimolecular nucleophilic substitution, prefer less-substituted carbons because the alkyl groups create steric hinderance and inhibit the nucleophile from accessing the electrophilic substrate carbon, rate dependent on concentrations of both the substrate and the nucleophile
One concerted step where nucleophile attacks at the same time as the leaving group lives, nucleophile must perform a backside attack (leads to inversion of stereochemistry - R to S or vise versa if leaving group and nucleophile have same priority)
Oxidation state
The charge an atom would have if all of its bonds were completely ionic, CH4 is the lowest oxidation state of carbon (most reduced) and CO2 is the highest (most oxidized)
Oxidation
An increase in the oxidation state and is assisted by oxidizing agents
Oxidizing agents
Accept electrons and are reduced in the process, they have a higher affinity for electrons or an unusually high oxidation state, they often contain a metal and a larger number of oxygens
Oxidation of primary alcohols
Primary alcohols can be oxidized aldehydes by pyridinium chlorochromate (PCC) or to carboxylic acid by stronger oxidizing agents such as chromium trioxide (CrO3) or sodium or potassium dichromate (Na2Cr2O7 or K2Cr2O7)
Oxidation of secondary alcohols
Can be oxidized to ketones by most oxidizing agents
Oxidation of aldehydes
Can be oxidized to carboxylic acids by most oxidizing agents
Reduction
Decrease in oxidation state and is assisted by reducing agents
Reducing agents
Donate electrons and are oxidized in the process, have low electronegativity and ionization energy, often contain a metal and a large number of hydrides
Reduction of aldehydes, ketones, and carboxylic acids
Can be reduced to alcohols by lithium aluminum hydride (LiAlH4)
Reduction of amides
Can be reduced to amines with LiAlH4
Reduction of esters
Can be reduced to a pair of alcohols with LiAlH4
Chemoselectivity
Both nucleophile electrophile and oxidation reduction reactions tend to happen at the highest priority or most oxidized functional group, one can make use of steric hindrance properties to selectively target functional groups that might not primarily react or protect functional groups (diols often protecting groups for aldehyde or ketone carbonyls, alcohols can be protected by conversion to tert-butyl ethers)
