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Ch 4 : Analyzing Organic Reactions
Terms in this set (31)
Lewis Acid - Electron Acceptor
An atom, ion, or molecule that accepts an electron pair to form a covalent bond
Tend to be electrophiles
Lewis Base - Electron Donor
An atom, ion, or molecule that donates an electron pair to form a covalent bond
Tend to be nucleophiles
Coordinate Covelent Bonds
Covalent bonds in which both electrons in the bond come from the same starting atom
a molecule or ion that is a proton donor
a molecule or ion that is a proton acceptor
Molecules that can act as both a Bronsted-Lowry Acid or Base
Ex : H20
The acidity and basicity of a molecule is dependent on its properties of the solution the molecule is in
Water can only act as a base in acidic solutions and as an acid in basic solutions
Acid Dissociation Constant - Ka
Measures the strength of an acid in solution
Ratio of the concentration of the dissociated form of an acid to the undissociated form
Stronger acids have larger K(a) values than weaker acids
Ionization constant of a chemical compound.
the pH at which half of the molecules of that species are deprotonated
Stronger acids have smaller pKa values than weaker acids, pKa = -logKa
The carbon adjacent to a carbonyl;
Because enol forms of carbonyl-containing carbanions are stabilized by resonance acidic hydorgens are easily lost
Hydrogen attached to the alpha-carbon
Due to the resonance stability of the carbonyl carbon, these hydrogns are easily lost and are typically the first to deprotonate
Acidity of Common Functional Groups
Alkanes < Alkenes < H2 < Amines < Alkynes < Ketones < Alcohols < Water < Carboxylic acids < Hydronium Ion
Alcohols, Aldehydes, Ketones, Carboxylic Acids, and Carboxylic Acid derivatives tend to act as acids - Are easier to target with nucleophilic reactants
Amines and Amides tend to act as bases - the Nitrogen of these compounds tend to form coordinate covalent bonds by donating a lone pair of electrons to the Lewis Acid
Nucleus loving species with either lone pairs or pi bonds that are used to form bonds with electrophiles
Tend to be electron rich and act similar to bases
Good nucleophiles tend to be good bases
Nucleophilicity is determined by reactions rates with common electrophiles - kinetic property
Basicity is dependent on the equilibrium position of the reaction - thermodynamic property
Anions (Br, OH, CN ions)
Alkenes and alkynes
Atoms with lone pairs (Water, and Ammonia)
Factors of Nucleophilicity
Charge - Nucleophilicity increases with increasing electron density, negative charge
Electronegativity - Nucleophilicity decreases with increasing electronegativity as atoms are less likely to share electrons
Steric Hinderance - Nucleophilicity decreases with larger bulkier molecules
Solvent - protic solvents decrease nucleophilicity, by protonating the nucleophile or through hydrogen bonding
Solvent Effects ???
In polar protic solvents, nucleophilicity increases down the periodic table
Common protic solvents are carboxylic acids, ammonia/amines, and water/alcohols. In polar aprotic solvents
In aprotic solutions, nucleophilicity increases up the periodic table. Common aprotic solvents are DMF, DMSO, and Acetone.
Electron loving species with a positive charge or positively polarized atom.
Accepts an electron pair when forming new bonds with a nucleophile
Greater degree of positive charge results in greater electrophilicity
Good Electrophiles : Carbocations, carbonyls, then alcohols
Electrophilicity and Acidity are identical properties
Molecular fragments that retain electrons after heterolysis
The best leaving groups will be able to stabilize the extra electrons.
Weak bases are more stable with an extra set of electrons and therefore make good leaving groups.
Conjugate bases of strong acids make good leaving groups.
Alkanes and hydrogens almost never serve as leaving groups - form very reactive basic ions
Essential opposite of coordinate covalent bond formation - when the bond is broken both electrons are given to 1 of the 2 products
Nucleophilic Substitution Reactions
Occurs when the nucleophile forms a bond with a substrate carbon and the leaving group leaves
SN1 and SN2 Reactions
Nucleophilic substitution reaction
Has 2 Steps :
1. Leaving group leaves generating positively charged carbocation
- Rate limiting step
2. Nucleophile attacks the carbocation resulting in the substitution product
An organic ion in which a carbon atom has a positive charge
Forms when the leaving group leaves the molecule
The formation and stabilization of this determines all other aspects of SN1 reactions
Unimolecular Nucleophilic Substitution
Bimolecular Nucleophilic Substitution
Nucleophilic substitution reaction
Has 1 Step :
Nucleophile attacks the compound at the same time as the leaving group leaves
Single rate-limiting step involved two molecules
Nucleophile attacks the compound at the same time as the leaving group leaves.
Single rate-limiting step involved two molecules.
Nucleophile displaces the leaving group this way.
Nucleophile must be strong and the substrate can't be sterically hindered.
Oxidizing Agents and Reactions
element or compound in redox reactions that accepts electron from another species
because it gains electrons, it is reduced
good oxidizing agents:
high affinity for electrons or have high oxidation states ; O2, O3, Cl2, MnO4-, CrO42-, dichromate and PCC; often contain a metal and a large # of oxygen atoms
Reducing Agents and Reactions
element or compound in redox reactions that loses electron from another species
because it loses electrons, it is oxidized
good reducing agents:
have low EN and ionization energies or contain a hydride ion (H-); often contain a metal and a large # of hydrides; examples are sodium, magnesium, aluminum, zinc, sodium hydride (NaH), calcium dihydride (CaH2), lithium aluminum (LiAlH4) and sodium borohydride (NaBH4)
Preference of one functional group over other functional groups
Steric Hinderance / Prevention
Prevention of reactions at a location.
Protects the reaction of synthesis formation.
Convert certain functional groups to prevent reactions from occurring.
Steps to Problem Solving
2. Identify functional groups
3. Identify reagents
4. Identify most reactive functional groups
5. Identify first step of the reaction
6. Consider steroselectivity
THIS SET IS OFTEN IN FOLDERS WITH...
Ch 1: Nomenclature
Chapter 2: Isomers
Ch 3: Bonding
Ch 5 : Alcohols
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