Orgo - General Principles Flashcards
What condition must be met for an acid-base reaction to take place?
It will only proceed if the products formed are weaker than the reactants
What is the definition of a Lewis acid?
Electron acceptor in the formation of a covalent bond
What is the definition of a Lewis base?
Electron donator in the formation of a covalent bond
What type of covalent bonds do acids and bases form?
Coordinate covalent bonds
What is the Bronsted-Lowry definition of an acid?
Species that can donate a proton
What is the Bronsted-Lowry definition of a base?
Species that can accept a proton
What are amphoteric molecules? Example?
Molecules that can either act as Bronsted-Lowry acids or bases
Water
What measures the strength of an acid in solution?
The acid dissociation constant
What is the equation of the acid dissociation constant?
Ka= [H+].[A-]/[HA]
What is the equation for the pKa?
pKa= -log Ka
How does pKa relate to the acidity of an acid? Ranges?
The greater the pKa the lower the acidity
pKa < -2 = strong acid
-2 < pKa < 20 = weak acid
What is the acidity trend in the periodic table?
Increases down the periodic table because of bond strength
Increases with electronegativity
When these two trends oppose each other, bond strength takes over
What is a special example of protons that are easily lost?
alpha Hs on the alpha C of carbonyl
What are 5 functional groups that act as acids?
- Alcohols
- Aldehydes
- Ketones
- Carboxylic acids
- Carboxylic acid derivatives
What are the 2 functional groups that act as bases?
- Amines
2. Amides
What do nucleophiles have?
A lone pair or electrons or pi bonds to form bonds with electrophiles
What is the main distinction between nucleophiles and bases?
Nucleophile strength depends on rate of reaction with electrophiles = kinetic property
Base strength depends on equilibrium position of a reaction = thermodynamic property
How do you identify most nuclephiles?
CHON with a minus sign or a lone pair
What are the 4 factors that determine nucleophilicity
- Charge: more negative = better nucleophile
- Electronegativity: more electronegative = worse nucleophile
- Steric hindrance: larger = worse nucleophile
- Solvent: protic solvents can protonate or H bond the nucleophile which decreases its reactivity
What do electrophiles have?
Positive charge or positively polarized atom that accepts an electron pair to form bonds with nucleophiles
What is the main distinction between electrophiles and acids?
Same as nucleophiles and bases
More positive compounds are more…
Electrophilic
What are leaving groups?
The molecular fragments that retain the electrons after heterolysis
What can the best leaving groups do?
Stabilize additional charge through resonance or induction
What are good leaving groups? Why?
Weak bases because they are more stable with an extra pair of electrons
Can alkanes and hydrogen ions be leaving groups? Why?
Almost never because they form reactive anions
What are heterolytic reactions?
The opposite of coordinate covalent bonding reactions: a bond is broken and both electrons are given to one of the two products
What are the 2 steps of unimolecular nucleophilic substitution reactions (SN1)?
- The leaving group leaves, forming a carbocation
2. The nucleophile attacks the planar carbocation from either side leading to a racemic mixture of products
What is a carbocation?
An ion with C+
What does “more substituted C” mean?
The carbon with the least amount of hydrogens attached and the most amount of other carbons or other non-hydrogen elements attached
What do SN1 reactions prefer? Why?
More substituted Cs because the alkyl groups can donate electron density and stabilize the positive charge of the carbocation
What is the rate of SN1 reactions only dependent on?
The concentration of the substrate
In SN1 reactions, which step is the rate limiting one?
The first step
Why do SN1 reactions form a racemic mixture?
Because the incoming nucleophile can attack the carbocation from either side, resulting in varied stereochemistry
What is the one concerted step of bimolecular nucleophilic substitution reactions (SN2)?
The nucleophile attacks at the same time as the leaving group leaves
How is the attack of the nucleophile called in SN2 reactions? Why?
Backside attack, because the nucleophile approaches the C at a 180 degree angle to the existing carbon-leaving group bond
What happens to the absolute configuration of the molecule when it is attacked by a nucleophile in SN2 reactions?
It is changed if the incoming nucleophile and the leaving group have the same priority in the molecule
What do SN2 reactions prefer? Why?
Less substituted Cs because the alkyl groups create steric hindrance and inhibit the nucleophile from accessing the C
What is the rate of SN2 reactions dependent on?
The concentrations of both the substrate and the nucleophile
How must the nucleophile and leaving group be related in order for a substitution reaction to occur?
The reaction will occur when the nucleophile is a stronger base than the leaving group
What trends increase electrophilicity?
Greater positive charge and better leaving groups
What is the oxidation state of an atom?
The charge it would have if all its bonds were completely ionic
What is the lowest oxidation state of C?
CH4
What is the highest oxidation state of C?
CO2
What is the order of functional groups from most oxidized to least oxidized?
- Carboxylic acids and derivatives
- Aldehydes, ketones, and imines
- Alcohols, alkyl halides, and amines
What happens to the reactants in a redox reaction?
Their oxidation states change
What is the oxidation state of ions?
Their charge
What does oxidation mean?
Increase in oxidation state = loss of electrons = increase in the number of bonds to O or other heteroatoms
What does reduction mean?
Decrease in oxidation state = gain of electrons = increase in the number of bonds to H
What happens to oxidation agents in redox reactions?
They accept electrons and are reduced
Are oxidation agents electrophiles or nucleophiles?
Electrophiles
What do oxidation agents often contain?
A metal and a large number of Os
What can primary alcohols be oxidized to (2)? By what?
- Aldehydes by pyrimidinium chlorochromate (PCC)
2. Carboxylic acids by stronger oxidizing agents like chromium trioxide (CrO3) or sodium potassium dichromate (Na2Cr2O7)
What are primary, secondary, and tertiary alcohols?
- Attached to a C with only one alkyl group
- Attached to a C with two alkyl groups
- Attached to a C with three alkyl groups
What can secondary alcohols be oxidized to? By what?
To ketones by most oxidizing agents
What can aldehydes be oxidized to? By what?
To carboxylic acids by most oxidizing agents
What happens to reduction agents in redox reactions?
They donate electrons and are oxidized
Do reduction agents have a low or high electronegativity?
Low
What do reduction agents often contain?
A metal and a large number of hydrides
What can aldehydes, ketones, and carboxylic acids be reduced to? By what?
To alcohols by lithim alumunium hydride (LiAlH4)
What can amides be reduced to? By what?
To amines by LiAlH4
What can esters be reduced to? By what?
To a pair of alcohols by LiAlH4
Where do nucleophile-electrophile and oxidation-reduction reactions tend to act?
At the highest-priority = most oxidized functional group
How can one selectively target functional groups that might not primarily react or protect leaving groups?
By making use of steric hindrance properties
What groups are often used to protect aldehyde or ketone carbonyls?
Diols
How can alcohols be protected?
By conversion to tert-butyl ethers
What are the two reactive centers of a carbonyl containing compound?
The carbonyl C and the alpha Hs
In which types of compounds are SN1 reactions most likely to occur?
Tertiary Cs
In which types of compounds are SN2 reactions most likely to occur?
Primary Cs
What are the 6 steps to problem solving for orgo reactions?
- Know your nomenclature
- Identify the functional groups
- Identify the other reagents
- Identify the most reactive functional group
- Identify the first step of the reaction
- Consider stereoselectivity
Most anhydrides are… which is caused by…
Cyclic because of dehydration of a dicarboxylic acid
How are anhydrides formed?
One H2O is removed and a bond is formed between 2 carboxylic acid molecules
