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MCAT Organic Chemistry Review > 4 Analyzing Organic Reactions > Flashcards

4 Analyzing Organic Reactions Flashcards

1
Q

Lewis Acid

A

electron acceptor in formation of covalent bond

often electrophiles

vacant p-orbitals

positively polarized atoms

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2
Q

Lewis Base

A

electron donor in formation of a covalent bond

often nucleophiles

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3
Q

coordinate covalent bond

A

Lewis acid + Lewis base

both electrons come from the same starting atom (Lewis base)

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4
Q

Bronsted-Lowry Acid

A

species that can donate a proton [H+]

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5
Q

Bronsted-Lowry Base

A

species that can accept a proton

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6
Q

amphoteric molecule

example?

A

ability to act as an acid OR base

ex. water

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7
Q

acid dissociation constant (Ka)

equation

A

strength of acid in solution

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

for HA <–> H+ + A-

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8
Q

pKa = ?

A

-logKa

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9
Q

more acidic solution’s = ?(higher/lower pKa)

A

lower pKa

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10
Q

pKa < -2

A

strongly acidic

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11
Q

pKa = -2 to 2

A

weak organic acids

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12
Q

alpha-hydrogens

A

VERY acidic

connected to alpha-carbon of carbonyls

stabilized by enol form resonance

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13
Q
A

nucleophiles

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14
Q

nucleophilicity and charge

A

nucleophilicity increases with increasing electron density (more negative charge)

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15
Q

nucleophilicity and electronegativity

A

nucleophilicity decreases as electronegativity increases (atoms less likely to share electron density)

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16
Q

nucleophilicity and steric hindrance

A

bulkier molecules are less nucleophilic

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17
Q

nucelophilicity and solvent

polar protic solvents?

polar aprotic solvents?

A

protic solvents can hinder nucleophilicity by protonating the nucleophile or through hydrogen bonding

polar protic solvents: nucleophilicity increases DOWN periodic table (protons are attracted to nucleophile and get in the way)

polar aprotic solvents: nucleophilicity increases UP periodic table (directly relates to basicity)

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18
Q

“electron-loving”

species with positive charge/positively polarized atom

tend to be good acids

A

electrophiles

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19
Q

increasing electrophilicity

A

more positive charge

better leaving groups

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20
Q

leaving groups

A

molecular fragmetns that retain electrons after heterolysis

best LGs are able to stabilize extra electrons

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21
Q

best leaving groups

A

weak bases (conjugate bases of strong acids lie I-, Br-, Cl-)

increased resonance

inductive effects from electron-withdrawing groups

delocalize/stabilize negative charge

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22
Q

SN1 reactions

A
  1. rate-limiting step: LG leaves, positively-charged carbocation remain
  2. nucleophilic attack on carbocation yields subsitution product
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23
Q

SN1 reaction passes through a planar intermediate and so will result in a ___________.

A

racemic mixture

24
Q

SN1 reaction is more likely to proceed with a _______(more/less) subsituted carbon.

A

more

(more stable carbocation)

25
Q

rate of SN1 reaction

A

rate = k [R-L]

[R-L] is alkyl group containing LG

1st order reaction: anything that accelerates formation of carbocation (Step 1) increases rate of SN1 reaction

26
Q

SN2 reactions

A

1 step (concerted reaction)

“backside attack”

requires STRONG nucleophile and non-sterically hindered substrate

27
Q

SN2 reaction proceeds best with _____ (more/less) substituted carbon.

28
Q

SN2 reactions are stereospecific. What does this mean?

A

the configuration of reactants determines the configuration of the products

inversion of relative configuration

AND if nucleophile and LG have same priority: inversion of absolute configuration

29
Q

rate of SN2 reaction

A

rate = k[Nu][R-L]

30
Q

oxidation-reduction reaction (redox)

A

oxidation states of reactants change

31
Q

oxidation state

A

indicator of hypothetical charge that an atom would have if all bonds were completely ionic

can be calculated from molecular formula

32
Q

oxidation

A

increases oxidation state

loss of electrons

33
Q

reduction

A

decrease in oxidation state

gain of electrons

34
Q

oxidizing agent

A

accepts electron from other species

high affinity for electrons (ex. O2, O3, Cl2)

unusually high oxidation states (ex. MnO4-, CrO4 2-)

35
Q

oxidation reagent?

alcohol –> aldehyde

A

PCC
CrO3/pyridine

36
Q

oxidation reagent?

alcohol –> ketone

A

PCC

CrO3/pyridine

37
Q

oxidation reagent?

aldehyde –> carboxylic acid

A

H2CrO3

KMnO4

H2O2

38
Q

oxidation reagent?

alcohol –> carboxylic acid

A

KMnO4

H2CrO4

39
Q

oxidation reagent?

alkane –> carboxylic acid

40
Q

oxidation reagent?

alkene –> aldehyde/ketone

A

O3, then Zn

O3, then CH3SH3

41
Q

oxidation reagent?

alkene –> carboxylic acid/ketone

A

O3, then H2O2

KMnO4, heat, H3O+

42
Q

oxidation reagent?

alkyne –> carboxylic acid

A

O3, then H2O2

KMnO4, heat, H3O+

43
Q

oxidation reagent?

alkene –> diol (vicinal diol)

A

OsO4

KMnO4, HO-

44
Q

oxidation reagent?

alkene –> epoxide

45
Q

oxidation reagent?

diol –> aldehyde

A

NaIO4

Pb(OAc)4

HIO4

46
Q

oxidation reagent?

ketone –> ester

47
Q

reducing agents

A

sodium, magnesium, aluminum, zinc (low electronegativities and ionization energies)

metal hydrides (H- ions)

48
Q

reduction reaction

aldehyde –> primary alcohol

A

LiAlH4/NaBH4

49
Q

reduction reaction

ketone –> secondary alcohol

A

LiAlH4/NaBH4

50
Q

reduction reaction

amide –> primary amine

A
  1. LiAlH4/ether
  2. H+/H2O
51
Q

reduction reaction

carboxylic acid –> primary alcohol

A
  1. LiAlH4/ether
  2. H2O
52
Q

reduction reaction

ester –> primary alcohols

A
  1. LiAlH4/ether
  2. H2O
53
Q

chemoselectivity

A

preferential reaction of one functional group in presence of other functional groups

increased oxidation of functional group increases reactivity (nucleophile-electrophile rxns and oxidation-reduction rxns)

54
Q

common reactive sites for chemoselective reactions

SN1?

SN2?

A

carbonyl carbon

substrate carbon in substitution reaction

SN1: tertiary/secondary C (stable carbocation)

SN2: methyl/primary C (decreased steric hindrance)

NO tertiary carbons

55
Q

steric hindrance

A

prevention of reactions at particular location within a molecule due to the size of the substituent groups

56
Q

steric protection

A

useful tool for synthesis of desired product

prevents alternate products

MCAT Organic Chemistry Review (9 decks)

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