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MCAT Org. Chem Ch. 4

QuestionAnswer
Lewis Acids Electron acceptors that have vacant orbitals or positively polarized atoms.
Lewis Bases Electron donors that have a lone pair of electrons and are often anions.
Bronsted-Lowry Acids Proton donors
Bronsted-Lowry Bases Proton acceptors
Amphoteric Molecules Can act as either acids or bases, depending on reaction conditions. ex: Water
Acid Dissociation Constant, ka Measure of acidity. It is also the equilibrium constant that corresponds to the dissociation of an acid, HA, into a proton, H+, and its conjugate base, A-.
pKa negative log of Ka
Note About A Lower pKa value This indicates a stronger acid
Note About pKa Periodic Trend pKa decreases down the Periodic Table and increases with electronegativity.
Common Acidic Functional Groups Include: Alcohols, aldehydes, ketones, carboxylic acids, and carboxylic acid derivatives
Alpha-Carbon A carbon adjacent to a carbonyl
Note About Alpha-Hydrogens And Their Acidity Hydrogens attached to an alpha-carbon are acidic
Nucleophiles "Nucleus-loving" molecules that contain a lone pair of pi-bonds. they also have increased electron density and carry a negative charge.
Note About Nucleophilicity's Property Type It is a kinetic property
Note About Basicity's Property Type It is a thermodynamic property.
Properties That Can Affect Nucleophilicity Charge, electronegativity, steric hindrance, and a solvent
Common Organic Nucleophiles Amino groups
Electrophiles "electron-loving" molecules that contain a positive charge or are positively polarized.
Note About Positive Compounds And Their Electrophilicity They are more electrophillic
Examples Of Electrophiles Alcohols, aldehydes, ketones, carboxylic acids and their derivatives.
Leaving Groups Molecular fragments that retain the electrons after heterolysis.
Note About Best Leaving Groups And Charge The best leaving groups can stabilize additional charge through resonance or induction.
Good Leaving Groups Weak bases (the conjugate bases of strong acids)
Reason Why Alkanes And Hydrogen Ions Are Rarely Leaving Groups They form reactive anions.
First Step Of Unimolecular Nucleophilic Substitution (SN1) Reactions The leaving group leaves and forms a carbocation.
Carbocation An ion with a positively charged carbon atom.
Second Step Of Unimolecular Nucleophilic Substitution (SN1) Reactions Nucleophile attacks teh planar carbocation from either side, which leads to a racemic mixture of products.
Reason Why SN1 Reactions Prefer More-Substituted Carbons Alkyl groups can donate electron density and stabilize the positive charge of the carbocation.
Rate Equation For SN1 Reaction rate = k[R-L]. This only depends on the concentration of the substrate
One Concerted Step For Bimolecular Nucleophilic Substitution (SN2) Reactions (FIRST PART) 1. The nucleophile attacks at the same time the leaving group leaves.
One Concerted Step For Bimolecular Nucleophilic Substitution (SN2) Reactions (SECOND PART) 2. The nucleophile must perform a backside attack, which inverts stereochemistry. 3. The abs. config. is changed from R to S (vice-versa) if the incoming nucleophile and leaving group have the same priority in the molecule.
Reason Why SN2 Reactions Prefer Less-Substituted Carbons The alkyl groups create steric hindrance and inhibit the nucleophile from accessing the electrophilic substrate carbon.
Rate Equation For SN2 Reaction rate = k[Nu:][R-L]. Rate is dependent on concentration of substrate.
Oxidation State Of An Atom The charge an atom would have if all its bonds were completely ionic.
Lowest Oxidation State of Carbon CH4
Highest Oxidation State of Carbon (Most Oxidized) CO2
List Of Greatest To Least Oxidized Groups Carboxylic acids, and carboxylic acid derivatives.Then, aldehydes, ketones, and imines. Then, alcohols, alkyl halides, and amines.
Oxidation Increase in oxidation state and is assisted by oxidizing agents.
Oxidizing Agents Accept electrons and are reduced in the process. They have a high affinity for electrons or an unusually high oxidation state. They often contain a metal and a large number of oxygens.
Note Of How Primary Alcohols Can Be Oxidized To Aldehydes By using Pyridinium chlorochromate (PCC) or to carboxylic acids by stronger oxidizing agents like chromium trioxide (CrO3) or sodium / potassium dichromate (Na2Cr2O7, K2Cr2O7)
Note Of How Secondary Alcohols Can Be Oxidized To Ketones By using most oxidizing agents.
Note Of How Aldehydes Can Be Oxidized To Carboxylic Acids By using most oxidizing agents.
Reduction Decrease in oxidation state and is assisted by reducing agents
Reducing Agents Donate electrons and are oxidized in the process. They have low electronegativity and ionization energy. They often contain a metal and a large number of hydrides.
Note Of How Aldehydes, Ketones, And Carboxylic Acids Can Be Reduced To Alcohols By using lithium aluminum hydride (LiAlH4)
Note Of How Amides Can Be Reduced To Amines By using lithium aluminum hydride (LiAlH4)
Note Of How Esters Can Be Reduced To A Pair Of Alcohols By using lithium aluminum hydride (LiAlH4)
Note About Nucleophile-Electrophile and Oxidation Reduction Reactions And Functional Groups They occur at the highest priority (most oxidized) functional group.
Note About Diols They are often used as protecting groups for aldehyde or ketone carbonyls
Note About Alcohols They may be protected by conversion to tert-butyl ethers.
Steps For Problem Solving: 1. Know your nomenclature. 2. Identify the functional groups. 3. Identify the other reagents. 4. Identify the most reactive functional group(s). 5. Identify the first step of the reaction. 6. Consider stereo selectivity.
Eq. 4.1 Acid Dissociation Constant Ka = [H+][A-] / [HA]
Eq. 4.2 Definition of pKa pKa = -log Ka
Created by: SamB91