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Fall2023 > OChem Reaction Types > Flashcards

OChem Reaction Types Flashcards

1
Q

Describe the SN1 reaction

A
  • 2 step carbocationization
  • results in racemic products
  • step 1 is RDS
  • step 2 is planar sp2 hybridized

Energy diagram has 2 humps
rate law is -d(sub)/dt= k(sub)
first order obs kinetics

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2
Q

Describe the SN2 reaction

A
  • must show TS
  • back side attack
  • concerted mechanism
  • inverted stereochemistry (stereospecific)

energy diagram is 1 hump
rate law is -d(sub)/dt= k(sub)(nucleophile)
second order obs kinetics

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3
Q

Describe the E1 reaction

A
  • 2 step carbocationization
  • second step planar (180 degree)
  • products are major minor or traces
  • stereoselective
  • indicator: 1.0 mol loc concentration base, alcohol (OH)

Energy diagram has 2 humps
rate law is -d(sub)/dt= k(sub)
first order obs kinetics

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4
Q

Describe the E2 reaction

A
  • 1 concerted step
  • anti-periplanar
  • stereoselective
  • products major minor or traces
  • show TS!
  • potential Newman Projections needed
  • indicators: strogn bases (better than OH), alkoxide (O-), large concentration bases

energy diagram is 1 hump
rate law is -d(sub)/dt= k(sub)(nucleophile)
second order obs kinetics

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5
Q

What is difference between stereospecific and stereoselective?

A
  • stereospecific mechanism specifies the stereochemical outcome of a given reactant
  • stereoselective reaction selects products from those made available by the same, non-specific mechanism acting on a given reactant– reesulting in different amounts of each product (major minor or traces)
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6
Q

What are the steps in determining the mechanism: SN1, SN2, E1, or E2?

A
  1. look at LG
    - if not one, no rxn
    - will not be F, acetate, or second row element (except S)
  2. substrate substituion structure (1, 2, 3 degree carbon)– number of things attached that are not H
    - 1 degree= no SN1 or E1
    - 2 degree= all posibilities kept
    - 3 degree= no SN2 bc slowed from sterics
  3. Nucleophile strength
    - strong base = E2
    - mediocre base= not E2 unless in excess amount
    - bad bases no elimination (must be SN1 or SN2)
  4. draw products (major, minor, traces)
  5. consider solvent
    - protic speeds up unimolecular processes
    - polar aprotic speeds up bimolecular processes
  6. consider sterics
    - bulky will slow down SN2
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7
Q

Protic solvents ________ all reactions

A

decrease

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8
Q

Polar aprotic solvents ________ all reactions

A

increase

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9
Q

how good are these leaving groups?

I-, Br-, Cl-, OTs-, OCF3-, OMs-, H2O

A

great!

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10
Q

how good are these leaving groups?

F-, CH3COO-, NH3

A

mediocre

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11
Q

how good are these leaving groups?

OH-, OCH3, NH2-

A

BAD

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12
Q

what are these solvents?

acetic acid, H2O, ROH, NH3

A

polar protic solvents (have at least 1 hydrogen that is connected directly to a particular electronegative atom)

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13
Q

what are these solvents?

DMF, nitromethane, acetone, aceonitrile, DMSO, ethyl acetate

A

Polal aprotic (a solvent that lacks an acidic proton/hydrogen and is polar)

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14
Q

what are these solvents?

alkanes, cycloalkanes, toluene, benzene, ether

A

Non-polar solvents (composed of atoms that have small differences in electronegativity)
* will never affect solvent rate

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15
Q

how good are these nucleophiles?

I-, HS-, RS-

A

very good!

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16
Q

how good are these nucleophiles?

Br-, HO-, RO-, CN-, N3-

A

good nucleophiles

17
Q

how good are these nucleophiles?

NH3, Cl-, F-, RCO2-

A

fair nucleophiles

18
Q

how good are these nucleophiles?

H2O, ROH

A

weak nucleophiles

19
Q

how good are these nucleophiles?

RCO2H

A

very weak nucleophiles

20
Q

how good are these bases?

NH2-, H-, HC(triple bond)C-

A

very strong!

21
Q

how good are these bases?

RO-, HO-

A

strong bases

22
Q

how good are these bases?

RNH2, Na2CO3

A

medicocre bases

23
Q

how good are these bases?

NH3, CN-, RCOO-, Cl-, BR-, I-, NaHCO3

A

weak bases

24
Q

what does a 1st degree substrate substitution indicate?

A
  • if strong base, SN2 is major and E2 is minor (but E2 is major if base is sterically hindered)
  • if weak base, only SN2
25
Q

what does a 2nd degree substrate substitution indicate?

A
  • if strong base E2 is major and SN2 is minor (SN2 will not occur if there is a sterically hindered nucleophile)
  • if polar protic, SN1 or E1
  • if polar aprotic, SN2
26
Q

what does a 3rd degree substrate substitution indicate?

A
  • if strong base, E2
  • if weak base, SN1 or E1
27
Q

what is the preferred substrate subsitiution of SN1, E1, and E2?

A

3 degree > 2 > 1 > methyl

28
Q

what is the preferred substrate subsitiution of SN2?

A

methyl&raquo_space;1degree» 2 > 3

Fall2023 (10 decks)

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