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MCAT OChem > Analyzing Organic Rxns > Flashcards

Analyzing Organic Rxns Flashcards

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MCAT flashcards
1
Q

Lewis acid

A

e- acceptor in formation of covalent bond
also tend to be electrophiles

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2
Q

Lewis base

A

e- donor
nucleophiles
usually lone pair

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3
Q

when Lewis acids and bases interact which type of bond is formed?

A

coordinate covalent
both electrons come from Lewis base

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4
Q

Brønsted-Lowry acid

A

proton donor

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5
Q

Brønsted-Lowry base

A

proton acceptor

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6
Q

amphoteric

A

can act as Brønsted-Lowry base or acid

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7
Q

Equilibrium constant

A

Ka = ([H+][A-])/[HA]

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8
Q

pKa

A

pKa = -logKa
acids w pKa below -2 are strong

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9
Q

Acidity as you move down periodic table

A

bond strength dec and therefore acidity inc

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10
Q

acidity and electroneg

A

the more electroneg, the higher the acidity

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11
Q

When bond strength is high w high electroneg OR bond strength is low with low electroneg

A

low bond strength takes precedence

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12
Q

functional groups highest to lowest pKa

A

alkane ~50>alkene ~43
>hydrogen 42>amine ~35
>alkyne 25>ester 25
>ketone 20-24>aldehyde 17-20
>alcohol 17>water 16
>CA 4>hydronium ion -1.7

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13
Q

Acidic fun groups

A

aldehydes
alcohols
ketones
CA
CA derivatives
Easier to target w basic or nucleophilic reactants bc they accept a lone pair

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14
Q

Basic fun groups

A

amines
amides
formation of peptide bonds
N of anime can form coordinate covalent bonds by donating lone pair to a Lewis acid

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15
Q

nucleophiles

A

“nucleus loving”
lone pairs or pi bonds that can form new bonds to electrophiles
good nucleophiles tend to be good bases
nucleophilicity is a kinetic property as it is depends on rate of rxn

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16
Q

4 factors that determine nucleophilicity

A

Charge (inc w inc e density)
Electroneg (dec as electroneg inc)
Steric hindrance (bulkier less nucleophilic)
Solvent (protic solvents can hinder nucleophilicity by protonating the nucleophile or via h bonding)

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17
Q

When nucleophilic molecules are in the same row or are the same atom…

A

the more basic the more reactive

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18
Q

nucleophilicity in polar protic solvents…

A

inc DOWN the periodic table

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19
Q

nucleophilicity in polar aprotic solvents…

A

inc UP the periodic table

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20
Q

Protic solvent

A

can H bond

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21
Q

Aprotic solvent

A

cannot H bond

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22
Q

Nucleophiles in polar solvents…

A

dissolve regardless of whether they’re aprotic or protic

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23
Q

Halogen nucleophilicity in protic solvents

A

I->Br->Cl->F-

Bc protons in solution will be attracted to the nucleophile

Conj bases of strong acids are less affected by protons in solutions and can react w electrophiles

24
Q

Halogen nucleophilicity in aprotic solvents

A

F->Cl->Br->I-

bc there are no protons to get in the way of the attacking nucleophile, in aprotic solvents nucleophilicity relates directly to basicity

25
Q

Nucleophile examples

A

Anime groups tend to make good nucleophiles

Strong:
HO-
RO-
CN-
N3-

Fair:
NH3
RCO2-

Weak:
H2O
ROH
RCOOH

26
Q

Electrophiles

A

-“electron-loving”
- pos charge or positively polarized atom that accepts electron pair when forming new bonds with a nucleophile
- Electrophilicity is a kinetic property tho unlike acidity
- They always act as Lewis acids tho
- Greater degree of positive charge inc electrophilicity, so a carbocation is more electrophilic than a carbonyl carbon

27
Q

CA derivatives ranked by electrophilicity

A

Anhydrides
CA
esters
Amides

derivatives of high reactivity can form those of lower but NOT vice versa

28
Q

Leaving group

A

Molecular fragments that retain electrons after heterolysis

29
Q

Heterolytic lysis

A
  • Opposite of coordinate covalent bond formation
  • A bond is broken and both e are given to one of the two products
  • Best LG will be able to stabilize extra electrons
30
Q

What make good LG

A

weak bases
More stable w an extra set of electrons
conj bases of strong acids make good LG

31
Q

What can better stabilize a LG negative charge?

A

resonance and inductive effects from EWG

32
Q

Nucleophilic substitution reactions

A

A nucleophile forms a bond w a substrate carbon and an LG leaves

33
Q

SN1

A

unimolecular sub rxns
2 steps:
1) rate limiting, LG leaves generating carbocation
2) nucleophile then attacks carbocation resulting in substitution product

  • the more substituted the carbocation the more stable it is because the alkyl groups act as electron donors, stabilizing the positive charge
  • rate = k[R—LG]
  • first order, substrate concentration dictates the rate and anything that accelerates the formation of the carbocation will inc the rate of an SN1 rxn
  • usually racemic bc of planar intermediate (nu can attack from either side)
34
Q

SN2

A

bimolecular nucleophilic substitution rxns

  • one step: nu attacks the compound at the same time as the LG leaves
  • therefore, a concerted rxn
  • single rate limiting step involves two molecules
  • nu actively displaces the LG in a backside attack
  • nu must be strong and substrate cannot be sterically hindered (less substituted the carbon, the more reactive to SN2 rxns)
  • opposite trend for SN1
  • rate = k[Nu][R—LG]
  • inversion (stereospecific rxn)
35
Q

oxidation states

A

CH4 ~> carbon has -4 oxidation state, most reduced

CO2 ~> carbon has +4 oxidation state, most oxidized

Oxidation Levels

0: alkanes
1: alcohols, alkyls halides, and amines
2: aldehydes, ketones, imines
3: CA, anhydrides, esters, and amides
4: CO2

36
Q

reduction vs oxidation

A

charge is REDUCED

Oxidation
Is
Loss of electrons

Reduction
Is
Gain of electrons

37
Q

oxidizing agent

A

accepting electrons (the thing getting reduced)

38
Q

reducing agent

A

electron loser (thing getting oxidized)

39
Q
  • PCC
  • CrO3/pyridine
A
  • 1° alcohols to aldehyde
  • 2° alcohol to ketone
40
Q
  • H2CrO4
  • KMnO4
A
  • w H2O2, aldehyde to CA
  • alcohol to CA
41
Q
  • KMnO4
A
  • alkane to CA
42
Q
  • O3 then Zn or CH3SCH3
A
  • alkene to aldehyde/ketone
43
Q
  • O3, then H2O2
  • KMnO4, heat, H3O+
A
  • alkene to CA/ketone
  • alkyne to 2 CA
44
Q

mCPBA

A
  • alkene to epoxide
  • ketone to ester
45
Q
  • OsO4
  • KMnO4, HO-
A
  • alkene to vicinal diol
46
Q
  • NaIO4 or Pb(OAc)4 or HIO4
A
  • diol to aldehyde
47
Q

LiAlH4/NaBH4

A
  • aldehyde to 1° alc
  • ketone to 2° alc
48
Q
  1. LiAlH4/ether
  2. H2O
A
  • amide to 1° amine
  • CA to 1° alcohol
  • ester to 2 1° alc
49
Q

Redox reagents tend to act on…

A

the highest priority functional group.

50
Q

reactions involving nucleophiles and electrophiles, the reaction tends to occur on…

A
  • the highest priority functional group because it contains the most oxidized carbon
  • a nucleophile is looking for a good electrophile and the oxidized carbon will allow the nucleophile to experience a greater partial positive
  • aldehydes are generally more reactive towards nucleophiles than ketones bc they have less steric hindrance
51
Q

why are a-carbons more acidic than regular CH bonds?

A
  • resonance stabilization of the enol form
52
Q

when it comes to carbocation formation, which carbons are preferred in SN1?

A

3° and 2°

53
Q

when is comes to carbocation formation, which carbons are preferred in SN2?

A

methyl and 1°

54
Q

steric hindrance

A
  • prevention of reactions at a particular location within a molecule due to the size of substituent groups
  • SN2 won’t occur on 3°
  • steric protection can be a useful tool in synthesis of desired molecules and the prevention of formation of alternative products
55
Q

protection during reduction

A
  • when several functional groups present, wise to convert aldehyde or ketone to a nonreactive acetal or ketal
  • HO(CH2)2OH and H+ to protect and H2O w H+ to reverse

MCAT OChem (11 decks)

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