Chapter 4- Analyzing Organic Reactions Flashcards
Lewis acid/base
acid- electron acceptor
base- electron donor
lewis acid
- electron acceptor
- electrophile
- positive charge
lewis base
- electron donor
- nucleophile
- anions (negative charge)
coordinate covalent bonds
formed when lewis acids and bases interact. they are covalent bonds in which both electrons in the bond came from the same starting atom (Lewis base)
bronsted-lowry acid/base
acid- donates H+
base- accepts H+
acid dissociation constant (Ka)
Ka = [H+][A-] / [HA]
pKa
pKa = -log(Ka)
- acidic molecules: smaller pKa
- basic molecules: larger pKa
electronegativity and acidity
the more electronegative an atom the higher the acidity
functional groups that act as acids
alcohols, aldehydes, ketones, carboxylic acids, most carboxylic acid derivatives
functional groups that act as bases
amines and amides
nucleophiles
BASES ARE NUCLEOPHILES.
ex: look for C, H, O, N with a minus sign or lone pair to identify most nucleophiles. (amines groups make good nucleophiles)
“nucleus-loving”
-with either lone pairs or pi bonds that can form new bonds to electrophiles
typical trends that determine nucleophilicity
- charge- increases with a more negative charge
- electronegativity- decreases as this increases
- steric hinderance- bulkier molecules are less nucleophilic
- solvent- explained in another flashcard
solvent effects
polar protic solvents (can H bond)
- ex: carboxylic acids, ammonia/amines, water/alcohols
- nucleophilicity increases down the periodic table
aprotic solvents (cannot H bond)
- ex: DMF, DMSO, acetone
- nucleophilicity increases up the periodic table
electrophiles
+ charge or positively polarized atom that accepts electron pair when forming new bonds with a nucleophile. typically lewis acids
-ex (in order from most electrophilic to least): anhydrides, carboxylic acids, esters, amides
-carbocations are very electrophilic
“electron-loving”
leaving groups
molecular fragments that retain electrons after heterolysis.
heterolytic reactions: a bond is broken and both electrons are given to one of the two products.
best leaving groups will be able to stabilize the extra electrons. (ex: weak bases and halogens)
substitution reactions
weaker base (leaving group) is replaced by the stronger base (nucleophile)
commonalities between Sn1 and Sn2 reactions
a nucleophile forms a bond with a substrate carbon and a leaving group leaves.
Sn1
2 steps (first-order reaction depending on reactants from step 1)
- rate limiting step- leaving group leaves generating a positively charged carbocation
* note: the more substituted this carbocation is the more stable it is - nucleophile then attacks the carbocation resulting in the substitution product.
*note: typically a racemic mixture is produced in Sn1 reactions
Sn2
1 step (aka. concerted reaction) 1. nucleophile attacks the compound at the same time the leaving group leaves
backside attack- nucleophile actively displaces the leaving group. MUST be a strong nucleophile to do this.
typical substrates: alkyl halide, tosylate, mesylate AND a nucleophile (second order reaction because it depends on both of these)
-wont occur with tertiary carbons
oxidation and reduction in O.Chem
OIL RIG
oxidation: increase in oxidation state
reduction: decrease in oxidation state
reduction = increasing the number of bonds to hydrogen
list of good oxidizing agents
high affinity for electrons (O2, O3, and Cl2)
unusually high oxidation states (Mn7+, permanganate MnO4-, and Cr6+ in chromate CrO4 2-)
what are primary alcohols oxidized to?
one level to become aldehydes and another level to become a carboxylic acid
what are secondary alcohols oxidized to?
ketones
typical trend in redox reactions
oxidation reactions- increase in number of bonds to oxygen
oxidizing agents- contain metals bonded to a large number of oxygen atoms
if the reagent is PCC whats typically gonna happen
alcohol turning into aldehyde or ketone
if the reagent is KMnO4 or H2CrO4 whats typically gonna happen
carboxylic acid forms onto the substrate
if the reagent is O3 whats typically gonna happen
double or triple bond will split into two separate molecules both with a double bond to oxygen where they were originally bonded to each other
list of good reducing agents
sodium, magnesium, aluminum, zinc (low electronegatvity)
metal hydrides (NaH, CaH2, LiAlH4, NaBH4) b/c they all contain a H- ion
aldehyde and ketone reduction
aldehydes- primary alcohol
ketones- secondary alcohol
general trend with reactivity in both nucleophile-electrophile and oxidation-reduction reactions
the more oxidized the functional gorup the more reactive it is
in a redox reaction AND nucleophile-electrophile reaction what part of the reagent is most likely to be part of the reaction
for BOTH it is the highest-priority functional group
common reactive site on MCAT
carbon on a carbonyl due to the positive polarity (negative polarity on the oxygen group)
protecting group
if a molecule contains multiple reactive functional groups then some of them will first be converted to a nonreactive group and serve as a protecting group then the reaction will proceed.
