Organic Chemistry Chapter 4: Analyzing Organic Reactions Flashcards
What is a lewis acid?
electron acceptors
What is a lewis base?
electron donor
What is a B-L acid?
proton donor
What is a B-L base?
proton acceptor
What are amphoteric molecules?
can act as either acids or based, depending on reaction conditions. ex. water
What is the acid dissociation constant?
Ka - a measure of acidity, the equilibrium constant corresponding to the dissociation of an acid into HA into a proton and its conjugate base
What is pKa?
the negative logarithm of Ka — the lower the pKa, the stronger the acid
What is the pKa trend in the periodic table?
decreases down the periodic table and increases with electronegativity
What are alpha hydrogens?
hydrogens connected to an alpha carbon (carbon adjacent to a carbonyl
What are common acidic functional groups?
alcohols, aldehydes, ketones, carboxylic acids and c.a. derivatives
What are common basic functional groups?
Amines and amides
What are nucleophiles?
nucleus loving and contain lone pairs or pi bonds. They have increased electron density and often carry a necative charge.
What can affect nucleophility?
charge, electronegativity, steric hinderance and the solvent
What are common nucleophiles?
amino groups
What are electrophiles?
electron-loving and contain a positive charge or are positively polarized.
What are common electrophiles?
alcohols, aldehydes, ketones, carboxylic acids & derivatives
What are leaving groups?
molecular fragments that retain the electrons after heterolysis. good leaving groups can stabilize additional charge through resonance or induction. Weak bases make good leaving groups.
What is heterolysis?
opposite of coordinate covalent bond formation - a bond is broken and both electrons are given to one of the two products.
What types are almost never leaving groups?
Alkanes and hydrogen ions because they form reactive anions
What are the steps of a unimolecular nucleophilic substitution?
- leaving group leaves, forming a carbocation, an ion with a positively charged carbon atom.
- the nucleophile attacks the planar carbocation from either side, leading to a racemic mixture of products
What do Sn1 reactions prefer?
more substituted carbons because the alkyl groups can donate electron density and stabilize the positive charge of the carbocation.
What is the rate of an Sn1 reaction dependent on?
only on the concentration of the substrate
What is a bimolecular Sn2 nucleophilic substitution?
Happens in one step - nucleophile attacks at the same time as the leaving group leaves.
What happens to the stereochemistry in an Sn2 reaction?
Nucleophile performs a backside attack, which leads to an inversion of stereochemistry.
What happens to the configuration if the incoming nucleophile and the leaving group have the same priority in the molecule?
Then absolute configuration is changed from R to S or vice versa.
What is the oxidation state?
The charge that an atom would have if all of its bonds were completely ionic
What is the lowest and highest oxidation state of carbon?
lowest - CH4
highest - CO2
What is the order of functional groups oxidation from most to least?
Carboxylic acids & derivatives > aldehydes > ketones and imines > alcohols > alkyl halides > amines
What is oxidation?
increase in oxidation state and is assisted by oxidizing agents
What are 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.
How can primary alcohols be oxidized?
to aldehydes by PCC
to carboxylic acids by CrO3 or Na2Cr2O7 or K2Cr2O7
How can secondary alcohols be oxidized?
to ketones by most oxidizing agents
How can aldehydes be oxidized to carboxylic acids?
most oxidizing agents
What is reduction?
Decrease in oxidation state and is assisted by reducing agents
What are 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
How can aldehydes, ketones and c.a. by reduced to alcohols?
LiAlH4
How can amides be reduced to amines?
LiAlH4
How can esters be reduced to a pair of alcohols?
LiAlH4
Where do nucleophile and electrophile generally act?
the highest-priority (most oxidized) functional group
What are used to protect leaving groups?
Diols are used to protect for aldehydes and ketone carbonyls
Alcohols can be protected by conversion to tert-butyl ethers
What are 6 steps to solving chemical reactions?
- know nomenclature
- identify the functional groups
- identify the other reagents
- Identify the most reactive functional group
- Identify the first step of the reaction
- consider stereoselectivity
What are common protic solvents?
carboxylic acids
ammonia/amines
water/alcohols
What are common aprotic solvents?
dimethylformamide (DMF), DMSO, acetone
Reagent: Alcohol to aldehyde
PCC or CrO3/pyrimidine
Reagent: Alcohol to Ketone
PCC or CrO3/pyrimidine
Reagent: Aldehyde to C.A.
H2Cr2O4, KMnO2, H2O2
Reagent: Alcohol to C.A.
H2Cr2O4, KMnO2
Reagent: Alkene to Carboxylic acid
KMnO4
Reagent: Alkene to Aldehyde/Ketone
O3, then Zn
O3, then CH3SCH3
Reagent: Alkene to C.A./Ketone
O3, then H2O2
KMnO4, heat, H3O+
Reagent: Alkyne to C.A.
O3, then H2O2
KMnO4, heat, H3O+
Reagent: Alkene to Diol
OsO4
KMnO4, HO-
Reagent: Alkene to Epoxide
mCPBA
Reagent: Diol to Aldehyde
NaIO4
Pb(OAc)4
HIO4
Reagent: Ketone to Ester
mCPBA
