Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Chem 210 > exam 3 - Sn1/Sn2/E1/E2 rxns > Flashcards

exam 3 - Sn1/Sn2/E1/E2 rxns Flashcards

You may prefer our related Brainscape-certified flashcards:
AP® Chemistry flashcards Periodic Table flashcards Chemistry 101 flashcards Organic Chemistry 101 flashcards
1
Q

what are the characteristics of a good leaving group?

A
  • conjugate bases of strong acids (Cl-, Br-, I-)
  • able to stabilize the negative charge upon departure
  • bonded to an sp3 C
  • bigger atoms are better leaving groups
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

how do you turn an alcohol into a good leaving group (besides protonation)?

A
  • use sulfonate ester and strong base (like pyridine)
  • mechanism: Cl leaves sulfonate ester and S grabs OH on molecule, the H then deprotonates and a strong base picks it up
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

what is a nucleophile

A
  • donates e- pairs to form new bonds
  • electron rich, negatively charged or neutral with lone pairs
  • ex: H2O, OH-, Cl-, NH3
  • acts as a lewis base
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

electrophile

A
  • accepts an e- pair to form a new bond
  • electron deficient, partial or fully positive charge
  • H+, NO2+, carbocations
  • acts as a lewis acid
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

what is the general mechanism for substitution rxns?

A

one sigma bond broken (departure of LG), one sigma bond formed (nucleophile attaches to electrophile)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

what is the mechanism/rate dependent on in an Sn1 rxn?

A
  1. loss of LG forms C+
  2. nucleophile attacks the C+
    - leads to racemic mix of products: if nucleophile attacks from side opposite to LG, inversion; if same side, retention
    - unimolecular (RDS involves 1 molecule/SM)
    - rate is dependent only on substrate concentration
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

what is the mechanism/rate dependent on in an Sn2 rxn?

A

1.nucleophile attacks from opposite side (backside)of LG while LG leaves
- with presence of chiral center, invert stereocenter @ Alpha carbon
- produces single product
- bimolecular (RDS involves 2 molecules)
- rate of reaction is dependent on concentration of nucleophile and substrate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

what is the general mechanism of elimination rxns?

A

two sigma bonds broken (one from LG and one from Beta hydrogen) and one Pi bond formed (C=C)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

what are the steps of an E1 rxn? what is the rate dependent on?

A
  1. LG leaves, forming a C+
  2. Beta hydrogen is removed
    - 2 step rxn
    - proceeds through C+
    - results in a C=C between Alpha and Beta carbons
    - unimolecular (RDS involves 1 SM that forms the C+)
    - rate depends on concentration of substrate
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

what must be true for Sn1/E1 rxns to occur?

A

the C+ intermediate must be stable.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

what do strong nucleophiles and strong bases favor?

A

strong nucleophiles favor substitution, and strong bases (especially strong hindered bases like tert-butoxide) favor elimination

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

what is the mechanism of an E2 rxn? what is the rate dependent on?

A
  1. LG and Beta hydrogen are removed simultaneously
    - Remove the Beta hydrogen that’s anti to the LG (use Newman projections –> rotate if not anti at first)
    - one step rxn, bimolecular
    - rate depends on concentration of substrate and base
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

what needs to be present for elimination rxns to occur?

A

Beta hydrogens

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

define heteroatom substituted

A

a carbon bonded to atoms other than C or O; becomes more electrophilic

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

define allylic

A

an allylic carbon is located next to a C=C and gains reactivity because the adjacent pi system can stabilize positive charges

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

define benzylic

A

a benzylic carbon is directly attached to a benzene ring; the ring’s resonance stabilizes positive charge

17
Q

define propargylic

A

a propargylic carbon is one carbon away from a C-C triple bond

18
Q

which type of reactions are the fastest? why?

A
  • bimolecular
  • they don’t have to go through a C+ intermediate
19
Q

classifications of lewis base- category a

A
  • good e- donor, weak base
  • anion, conjugate acid pKa < 15, uncharged sp3 N/S/P
  • degree of Alpha carbon: 1- Sn2, 2- Sn2, 3- no Sn2, no E2
  • ex: Cl-, Br-, I-, N3-, CN-, H2S-, R3P, R3N, RSH, HS-, RS-
20
Q

classifications of lewis base- category b

A
  • good e- donor, moderate base
  • anion, conjugate acid pKa ~ 15-30
  • degree of Alpha carbon: 1- Sn2, 2- E2 (if no B-H, Sn2), 3- E2
  • ex: OH-, H3CO-, H3CH2CO-
21
Q

classifications of lewis base- category c

A
  • good e- donor, strong base
  • conjugate acid pKa >30, hindered conjugate acid pKa > 10
  • degree of Alpha carbon: 1- E2 (no B-H, Sn2), 2- E2, 3- E2
  • DBU, H:-, tBuO-
22
Q

classifying lewis base- category d

A
  • poor e- donor, weak base
  • non-resonance stabilized C+: 1 and 2 degree Alpha carbon- no Sn/E, 3 degree- Sn1/E1
  • resonance stabilized C+: Sn1/E1
  • H2O, R-OH
23
Q

describe the effects of steric hindrance on the Alpha carbon on rxn rates and possibilities

A
  • degree of substitution of Alpha carbon once LG leaves: 0-2 (not sterically encumbered), 3 (sterically encumbered)
  • if Alpha carbon is sterically encumbered, Sn2 is impossible
  • rxn rates: Sn1/E1- higher degree of substitution at Alpha carbon increases rxn rates due to stability, Sn2- lower degree of substitution favors faster rxns due to less steric hindrance, E2- more substituted Alpha carbons favor faster rxns due to the formation of more stable alkenes
24
Q

describe the different types of solvents

A
  • polar protic solvents: can donate a proton (has H that could be acidic)
  • polar aprotic solvents: can’t donate proton (acetone, DMSO, DMF)
25
Q

when are polar protic solvents needed?

A
  • in Sn1/E1 rxns
  • they are things like water, alcohols, things that can H bond (H on N, O, F)
26
Q

describe the effects of solvents and rxn rates

A
  • polar protic solvents: slow down Sn2/E2 rxns because they form a solvent shell around the nucleophile/lewis base
  • solvent traps the nucleophile and slows the rxn
27
Q

when are polar aprotic solvents needed?

A
  • in Sn2/E2 rxns
  • they are things like acetone (O=C(CH3)2), DMF (HC=ON(CH3)2), and DMSO (O=S(CH3)2)
  • can’t use polar protic solvents because they form a shell of solvent around nucleophile/base
28
Q

define bimolecular, which reactions are biomolecular, what the rxn rate depends on, and what their energy diagrams look like

A
  • two reactants interact in a single step
  • Sn2/E2 (1 step involving two things)
  • Sn2 rate depends on concentration of nucleophile and electrophile, E2 rate depends on concentration of substrate and base
  • both energy diagrams are a single, smooth curve
29
Q

what degree of substitution allows Sn2 to occur?

A

1-2

30
Q

what degree of substitution allows Sn1 to occur?

A

2-3

31
Q

giveaways for Sn1

A
  • LG/potentially good LG
  • weak nucleophile (H2O, R-OH, CH3COOH (acetic acid), H3C-OH (methanol), AgNO3, acid)
  • 2-3 degree substituted C+
  • stable C+
  • acid as reactant/product
32
Q

giveaways for E1

A
  • B-hydrogens
  • stable C+ (3 degree substituted)
  • weak base as reagent
33
Q

giveaways for Sn2

A
  • strong nucleophile (CN, negatively charged, large, low EN)
  • 1-2 degree substituted alpha carbon
34
Q

giveaways for E2

A
  • nuclephile reagent is a strong base (negatively charged N and O: (CH3)2CO-, DIPEA, other strong BULKY BASE!!!)
35
Q

what hydrogen do you abstract in an E2 rxn?

A

beta hydrogen

Chem 210 (7 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions