Analyzing Organic Reactions Flashcards
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
The more _____ the carbocation, the more _____ it is due to alkyl groups stabilizing the positive charge
substituted
stable
For SN1, the rte of the reation depends only on the concentration of the substrate
rate = k [R-L] where R-L is the thing that contains the leaving group
SN2 Reaction
1) nucleophile attacks the compound at the same time as the leaving group leaves
known as a concerted reaction (1 step)
nucelophile displaces the leaving group through a back side attack, thus the substrate cannot be sterically hindered. THEREFORE, the less subsituted carbon, the more reactive it is to SN2 reactions
there will be an inversion of the relative configuration
Rate of SN2 reaction determined by concentration of both the nucleophile and the original substrate
rate = k [Nu] [R-L]
When SN2 reaction occur, the position of subsituents around the carbon will be ____. an R will become an _____
inverted
S
Oxidation State
indicator of hypothetical chage an atom would have if all the bonds were completely ionic
Oxidation of Derivatives (most to least)
Carboxylic Acids > Aldehydes >Ketones > Imines > alcohols > alkl halides > amines
Oxidation
increase in oxidation state, lossing electrons or increasing number of bonds to oxygen and other hetero atoms (non C and H atoms)
Reduction
decrease in oxidation state, gain in electrons
increase in the number of bonds to hydrogen
Oxidation of Carbon
when bond betwe C - less electronegative atom is replaced by C - more electronegative atom (c’s nitrogen, oxygen, halides)
Oxidizing Agent
is the element/compound which accepts the electron and
is reduced
good ones have high affinity for electrons or high oxidation states
Oxidation reactions tend to feature an ____ in the bonds to oxygen while oxidizing agents often contain ______ bonded to a large number of oxygen atoms.
increase
metals
Reduction of a Carbon
when a bond between a Carbon and an atom that is more electronegtaive gets replaced with Carbon with less electronegative atom
increasing bonds to hydrogen mostly
Good reducing agents
low electronegticities and ionization energies (sodium, magnesium, alumnimu, zinc)
or those with H- ion
Aldehydes and Ketones will be reduced to ____ and ____ alcohols respectively but slowly without a catalyst. (LiAlH4)
Amides can be reduced to amines using _______ which can also reduce carboxylic acids to _______ and esters to a pair of _____
primary and secondary
LiAlH4
primary alcohols
alcohols
Chemoselectivity
preferential reaction of one functional group in the presence of another functional group
A redox reagent will tend to act on the ______ priority fxnal group. Thus a molecule with alcohol/carboxylic acid will most likely react on a carboxylic acid than a alchol. This is because they have the _____ carbon.
More oxidized the carbon, the ____ electronegative groups around it and a more ____ charge for an electrophile to attack.
highest
most oxidized
more
positive
Priority of Functional Groups
Carboxylic Acids and Derivatives, Aldehyde/Ketone, Alcohol, Amine
Carbon of A Carbonyl
1) carbonyl carbon has positive charge due to electronegativity of oxygen, this causes alpha Hydrogen to be pulled away by strong base forming an enolate
2) enolate is strong nucleophile (oxygen has 3 lone pairs) and with electrophile can get a Hydrogen and form an enol
Sn2 vs Sn1 Favorability
Sn1: tertiary > secondary > primary
Sn2: Primary > Secondary > tertiary
Steric Hinderance
prevention of reactions at a particular location due to a substituent groups.
Steric protection
useful in synthesis of desire molecules by making it impossible for nucleophile to reach the most reactive electrophile
can also mask a reactive leaving group by forming a protecting group (aldehyde/ketone to acetal/ketal) to protect the functional groups
Steps To Problem Solving
1) Known Nomenclature
2) Identify Functional Groups
4) Identify other reagents
4) Identify the Most Reactive Functional Groups
5) Identify First step of the Reaction
6) Consider Steroselectivity
