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MCAT Organic Chemistry: Ch4: Analyzing Organic Reactions

Terms in this set (78)

Lewis definition focuses on
Transfer of electrons and formation of covalent bonds
Bronstead-Lowry definition focuses on
Proton (h+) transfer
Lewis acid
Electron acceptor in formation of covalent bonds.
Tend to be electrophiles
Lewis base
Electron donor in the formation of a covalent bond. Tend to be nucleotides. Donate LP
Bronstead-Lowry acid
Can donate a proton
Bronstead-Lowry base
Can accept a proton
Acid dissociation constant (Ka)
Measures the strength of an acid in solution
Ka equals
[H+][A-]
————
[HA]
Calculate pKa
pKa=-logKa
Small (or even -) pKa means
Acidic
Large pKa means
Basic
pKa below -2 means
It's a strong acid.
Strong acids compeletely
Dissociate in AQ solutions
Weak acids are ---- bases
Strong
& strong acids are weak bases. Opposite
The more electronegative, the higher the ----
Acidity
As bond strength decreases, acidity ----
Increases
Acidic functional groups
Alcohols, aldehydes, ketones, carboxylic acids, anhydrides, and ester
Basic functional groups
Amide and amine
Nucleophiles
"Nucleus loving". With either LP or a pi bond. Forms new bonds.

RO>HO>ROH>ROOH
Good Nucleophiles tend to be good ---
Bases
Nucleophile strengrh
Relative to rate of reaction, therefore is a kinetic property
Base strength
Related to equilibrium position, therefore is a thermodynamic property
The more basic the Nucleophile, the --- reactive it is
More
Charge & Nucleophilicity
Nucleophilicity decrease with increase in negative charge
Electronegativity & Nucleophilicity
Nucleophilicity decreases as electronegativity increase bc these atoms are less likely to share their electrons
2 determinants of Electrophicity
1)charge--greater + charge
2)better LG increases E making the reaction more likely to proceed
4 determinants of nucleophicity
1) charge (more negative--better N)
2) EN (more EN worse N)
3) Steric hindrance (larger-worse N)
4) solvent (protic (H bond I>Br>CL>F) can protonate or H bond with N--decreasing its reactivity)
Steric hindrance and Nucleophilicity
Bulkier molecules are less Nucleophilic
Difference bt nucleophicity and electrophicity and acidity and basicity
N and E: based on relative rates of reaction: kinetic properties

A and B: measured by the position of equilibrium in a pronation or deportation reaction:: Thermodynamic properties
Protic solvents
High H+ solution. Protonates. Can H bond
Nucleophilicity decreases as basicity increases
Aprotic solvents
Can't h bond
Nucleophilicity increases with basicity.
Ex of protic solvents
Carboxylic acids, ammonia/amines, water/alcohols
Ex of aprotic solvents
DMF, DMSO, acetone
Polar solvents
Whether aprotic or protic, can dissolve Nucleophiles and can assist in reactions where electrons are moved.
HI is a --- acid
Strong
HF is a ---- acid
Weak
Ex) Strong Nucleophiles
HO-, RO-, CN-, and N3-
Ex) fair Nucleophiles
NH3 & RCO2-
Ex) weak nucleophiles
H2O, ROH, and RCOOH
Electrophiles
"Electron-loving". Species with +charge or positively polarized atoms that ACCEPTS an electron pair (Lewis acid)
Which is the better electrophiles? Carbonation(C+) or carbonyl (C=O)
Carbocation!
What is more electrophilic? (Rank: carboxylic acid, ester, anhydride, and amine)
Anhydride>carboxylic acid> ester> amine
Conjugate bases of strong acids make --- Leaving Groups
Great!
-I,-Br, -Cl
Unimolecular Nucleophilic substitution (SN1) reaction
2 steps. Step 1= loss of LG and Carbocation formed
Step 2=Nucleophilic attack
SN1 Rate limiting step (RLS) is ---
Step 1= formation of Carbocation
SN1 is a --- order rxn
First order. Rate=k[R-L]
R-L is the alkyl group containing a leaving group.
SN1, the more substituted the Carbocation, the --- stable
More, it can stabilize the positive charge
SN1 forms a --- ---
Planar intermediate, giving rise to a racemic mixture of the product
Biomolecular Nucleophilic substitution (SN2) reaction
Only one step, Nucleophile attacks the compound at the same time as the leaving group leaves.
Single RLS involves 2 molecules
SN2 reaction requires --- nuc: & substrate to be ---
Back side attack. Requires a strong Nuc: & for the substrate to not be sterically hindered.
SN2 rate
Rate=k[Nuc:][R-L]
SN2 reactions can do what to absolute configuration?
Change it. From R to S or vice Versa
Oxidation-reduction (redox) reactions
Oxidation states of the reactants change.
Rank for oxidation states (carboxylic acid, alkyl halides, aldehydes, alcohols, amines, ketones, and imines)
ca>ald>ket>imine>alco>ah>amines
Oxidation
Increases oxidation state, loss of electrons, and increases number of bonds to heteroatoms O
reduction
decreases oxidation state, GAINS electrons, and increases the number of bonds to hydrogen
oxidizing agent
element or compound that ACCEPTS an electron
Gets REDUCED
Good oxidizing agents
high affinity for oxygen or have high oxidation states
ex) of good oxidizing agents
O3, O2, and Cl2 permanganate MNO4- chromate CrO4- dichromate CrO7 2-
Strong oxidizing agents (end product?)
take a primary alcohol or a lower level functional group and oxidizes it to become a carboxylic acid.
ex) strong oxidizing agents (2)
chromium trioxide (CrO3) and sodium or potassium dichromate (Na2Cr2O7 and K2Cr2O7)
Most oxidized to most reduced
methane, co2, ketone, alcohol, cooh
co2>cooh>ketone>alcohol>methane
What reagent will stop oxidation at an Aldehyde or Ketone?
PCC (pyrimidium chlorochromate)
aldehyde from primary alcohol
ketone from secondary alcohol
Oxidation reactions tend to cause a(n) _______ (increase/decrease) in the number of bonds to oxygen
increase
oxidizing agents often contain metals bonded to a large number of ______
Oxygens
Reducing agent
what becomes oxidizes, and loses electrons
good reducing agents include (what elements)
Low EN and IE (H) Na, Mg, Al, and Zn
ex) of good reducing agents (4) contains Hydrides (H-)
NaH, CaH2, LiAlH4, and NaBH4
when to use LiAlH4
when reducing carboxylic acids, amides, and more oxidant compounds to primary and secondary alcohols
Reduction reaction tends to cause a increase in the number of bonds to ____
hydrogen
Reducing agents often contain Metals bonded to large number of _____
hydrides
Reducing agents is to ____ as oxidizing agents is to _____
reducing agents to hydrides (H-)
oxidizing agents to oxygens (O)
alpha hydrogens
more acidic than other hydrogens
steric hinderance
the prevention of reactions at a particular location within a molecule due to the size of the substituent groups
protecting groups
when a ketone or aldehyde is converted to a ketal or acetal, which allows for another (less reactive) group to be targeted
SN1 reactions are most likely to occur on ____ carbons
tertiary
SN2 reactions are most likely to occur on ____ carbons
primary or secondary
common protecting groups
DIOL
[(Os on each side)
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