ORGO Ch. 4 Analyzing Organic Reactions Flashcards
What is the diff b/w Lewis and Bronsted theory?
Lewis’s definition is the transfer of electrons, while Bronsted-Lowry’s definition is the transfer of protons
When will an acid-base reaction proceed?
only when the conjugate acid and base are weaker than the original reactants
What is a Lewis Acid?
An electron acceptor due to vacant p-orbital, and electrophile
What is a Lewis base?
An electron donor due to a lone pair that can be donated, and a neutrophile
What is formed when Lewis acid and bases interact?
coordinate covalent bonds
What is a bronsted-lowry acid?
a species that can donate a proton (H+)
What is a bronsted-lowry base?
a species that can accept a proton (H+)
What is amphoteric?
species that can act as both a bronsted acid and base such as water, bicarbonate, and dihydrogen phosphate (H2P)
What does water become when it donates and accepts a proton?
In an acid solution, water donates a proton, it becomes a conjugated base, OH-
In a basic solution, water accepts a proton, it becomes a conjugated acid H3O+
What is the acid dissociation constant equation?
Ka = [H+] [A]/ [HA]
pKa = - log Ka
where Ka is the equilibrium constant for the dissociation of an acid
What does a negative and positive pKa mean?
an acidic molecule will have a smaller or negative pKa, and more basic molecules will have a larger pKa
What are the pKa values of strong acids and bases?
pKa < -2 are considered strong acids and dissociate completely in aqueous solutions
pKa > -2 are considered strong bases
Which functional groups act as acids?
alcohols, aldehydes and ketones, carboxylic acids and its derivates
Which functional groups act as a base?
amides and amines
What is the acidic trend in the period table?
bond strength decreases down the period table, and acidity (pKa) therefore increases. the more electronegative an atom, the higher the acidity
What are the 4 major factors that determine nucleophilicity?
the more negatively charged the molecule is, the better the nucleophile. The more electronegative an atom, the poorer the nucleophile. bulkier molecules and tertiary substrates are less nucleophilic
What happens to the nucleophilic in polar solvent?
it dissolves
What is a strong NU?
HO-, RO-, CN-, N3- > NH3, RCO2-
What is a weak NU?
H20, alcohol (ROH), and carboxylic acid (RCOOH)
What is an electrophile?
an electron-loving species with a positive charge. acts as a Lewis acid in reactions
What is the ranking of electrophilicity of carboxylic acids?
anhydrides are the most reactive, followed by carboxylic acids and esters, and then amides
What is the diff b/w electrophilicity and acidity?
electrophilicity and nucleophilicity a kinetic properties, whereas acidity and basicity a thermodynamic property
Why are weak bases good for leaving groups?
weak bases are most stable with an extra set of electrons that result from heterolysis
Describe the steps of an SN1 reaction.
the first step (rate-limiting) is when the leaving group leaves, generating a positively charged carbonation, and then the nucleophile attacks that carbonation, resulting in the substitution product in step 2.
What is the hallmark of an SN1 vs SN2 reaction?
SN1 - A Racemic mixture
SN2 - R/S configuration
Describe the steps of an SN2 reaction.
in a 1 step reaction, the nucleophile attacks the compound at the same time the leaving group leaves
What is oxidation and reduction?
oxidation is a loss of electrons (Lewis bases), and reduction is a gain of electrons (Lewis acids)
What functions group has zero oxidation level?
alkanes
What functions group has one oxidation level?
alcohols, alkyl halides, and amines
What functions group has two oxidation levels?
aldehydes, ketones, and imines
What functions group has three oxidation levels?
carboxylic acids, anhydrides, esters, and amides
What functions group has four oxidation levels?
carbon dioxide (CO2)
What is an oxidizing agent?
an element that accepts an electron from another, and becomes reduced.
What are the strong oxidizing agents?
O2, O3, Cl2, Mn7+, permanganate (MnO4-), chromate (CrO4-), Cr6+, CrO4(2-), Na2Cr2O7, K2Cr2O7, KMnO4, H2CrO4
What can primary alcohols be oxidized to?
an aldehyde (with a weak oxidizing agent like PCC), or further oxidized to form a carboxylic acid (with a strong oxidizing agent)
What can secondary alcohols be oxidized to?
ketones using PCC, or CrO3/pyrimidine
What are the good reducing agents?
H+, H20, Na, Mg, Zn, aluminum (Al), sodium hydride (NaH), calcium dihydride (CaH2), LiAlH4, ether, sodium borohydride (NaBH4)
What makes something a good reducing agent?
low electronegativity and ionization energy, or contain a hydride (H-) ion
What can aldehydes and ketones be reduced to?
primary and secondary alcohols using lithium aluminum hydride (LiAlH4)/NaBH4
What can amides be reduced to?
amines using LiAlH4/ether or H+/H2O
What can esters and carboxylic acids be reduced to?
primary alcohols and esters using LiAlH4/ether or H2O
What is an idol?
2 equivalents of alcohol
How are acetals and ketals formed?
acetal = aldehyde + idol
ketal = Keton + Idol
What is the rate-limiting step in an SN1 and SN2 substitution reaction?
SN1 - on the concentration of the substrate (1st order)
SN2 - on the concentration of both the substrate and the nucleophile (2nd order)
What is the order of oxidation amongst function groups?
carboxylic acids and their derivates are the most oxidized, followed by aldehydes, ketones, amines, and lastly alcohols, alkyl halids, and amines
What can alkanes and aldehydes be oxidized to?
carboxylic acids using H2CrO4, KMnO4, or H2O2
What can alkenes and alkynes be oxidized to?
carboxylic acids using O3/H202, or KMn04/H30/heat
What can diols be oxidized to?
aldehydes using NaIO4, Pb(OAc)4, or HIO4
What can ketones be oxidized to?
Esters using mCPBA
When will a substitution reaction proceed?
when the nucleophile is a stronger base than the leaving group
When is an SN1 vs SN2 reaction most likely to occur?
SN1 is most likely to occur o tertiary carbon where the carbonation can be most easily stabilized
SN2 is more likely to occur on methyl or primary carbons because there is less steric hindrance
What is the order of the best nucleophiles in a protic solvent?
I-, Br-, Cl-, F-
What is the order of the best nucleophiles in an aprotic solvent?
F-, Cl-, Br-, I-
What is the most and least stable leaving groups?
the most stable leaving group is H20, and the last is H-
