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MCAT OChem > Analyzing Organic Rxns > Flashcards

Analyzing Organic Rxns Flashcards

(55 cards)

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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

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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

Study These Flashcards
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
Nucleophile examples
Anime groups tend to make good nucleophiles Strong: HO- RO- CN- N3- Fair: NH3 RCO2- Weak: H2O ROH RCOOH
26
Electrophiles
-“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
CA derivatives ranked by electrophilicity
Anhydrides CA esters Amides derivatives of high reactivity can form those of lower but NOT vice versa
28
Leaving group
Molecular fragments that retain electrons after heterolysis
29
Heterolytic lysis
- 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
What make good LG
weak bases More stable w an extra set of electrons conj bases of strong acids make good LG
31
What can better stabilize a LG negative charge?
resonance and inductive effects from EWG
32
Nucleophilic substitution reactions
A nucleophile forms a bond w a substrate carbon and an LG leaves
33
SN1
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
SN2
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
oxidation states
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
reduction vs oxidation
charge is REDUCED Oxidation Is Loss of electrons Reduction Is Gain of electrons
37
oxidizing agent
accepting electrons (the thing getting reduced)
38
reducing agent
electron loser (thing getting oxidized)
39
- PCC - CrO3/pyridine
- 1° alcohols to aldehyde - 2° alcohol to ketone
40
- H2CrO4 - KMnO4
- w H2O2, aldehyde to CA - alcohol to CA
41
- KMnO4
- alkane to CA
42
- O3 then Zn or CH3SCH3
- alkene to aldehyde/ketone
43
- O3, then H2O2 - KMnO4, heat, H3O+
- alkene to CA/ketone - alkyne to 2 CA
44
mCPBA
- alkene to epoxide - ketone to ester
45
- OsO4 - KMnO4, HO-
- alkene to vicinal diol
46
- NaIO4 or Pb(OAc)4 or HIO4
- diol to aldehyde
47
LiAlH4/NaBH4
- aldehyde to 1° alc - ketone to 2° alc
48
1. LiAlH4/ether 2. H2O
- amide to 1° amine - CA to 1° alcohol - ester to 2 1° alc
49
Redox reagents tend to act on…
the highest priority functional group.
50
reactions involving nucleophiles and electrophiles, the reaction tends to occur on…
- 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
why are a-carbons more acidic than regular CH bonds?
- resonance stabilization of the enol form
52
when it comes to carbocation formation, which carbons are preferred in SN1?
3° and 2°
53
when is comes to carbocation formation, which carbons are preferred in SN2?
methyl and 1°
54
steric hindrance
- 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
protection during reduction
- 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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