tetrahedral, no unused p orbital
🧪ORGANIC CHEMISTRY STUDY GUIDE
SN1, SN2, E1, and E2 Reactions
Compare substitution and elimination mechanisms using substrate, nucleophile, base, and solvent.
8 key ideas8 flashcards5 practice questions
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Geometry tells you where the p orbitals can meet.
planar with one p orbital
linear with two p orbitals
Key ideas to know
Start with the relationships between ideas. Then close the notes and explain each one from memory.
- 01
SN2 is concerted and produces inversion at the reacting center.
- 02
SN1 forms a carbocation intermediate.
- 03
E2 requires an anti-periplanar hydrogen and leaving group.
- 04
Strong bulky bases often favor elimination.
- 05
Polar protic solvents support ion formation in SN1 and E1.
- 06
SN2 rate depends on both substrate and nucleophile concentrations.
- 07
SN1 and E1 share a carbocation-forming slow step and may compete under the same conditions.
- 08
E2 regiochemistry depends on substrate geometry and which beta hydrogens the base can reach.
PART OF THE ACS ORGANIC CHEMISTRY GUIDE
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Open the full ACS Organic Chemistry guide →Two ideas worth correcting now
NOT QUITE
→A strong base always gives E2 only
USE THIS INSTEAD
Substrate, steric crowding, solvent, and temperature also affect competition.
NOT QUITE
→SN1 always gives a perfectly racemic product
USE THIS INSTEAD
Ion pairing and local structure can produce unequal attack from the two faces.
Flashcards
Answer before opening each card. The effort to retrieve is part of the learning.
1What is the SN2 rate law?Show answer ＋
Rate = k[substrate][nucleophile].
2Which substrates favor SN1?Show answer ＋
Tertiary substrates and other structures that form stable carbocations.
3What stereochemical result is associated with SN2?Show answer ＋
Inversion of configuration.
4Can rearrangements occur in SN1?Show answer ＋
Yes, carbocation rearrangements can occur.
5What geometry does E2 require?Show answer ＋
The beta hydrogen and leaving group should be anti-periplanar.
6What is the SN1 rate law?Show answer ＋
Rate = k[substrate].
7Which mechanism is favored by a primary substrate and strong unhindered nucleophile?Show answer ＋
SN2.
8Which mechanisms can rearrange?Show answer ＋
SN1 and E1 because they pass through carbocations.
Explain it in your own words
Use the answer as a check after you have written or spoken your response.
01Why does a tertiary substrate resist SN2?
Steric crowding blocks backside attack.
02How does heat affect substitution versus elimination?
Higher temperature often favors elimination because it increases the importance of entropy.
03Why can a bulky base favor the Hofmann product?
It removes the most accessible beta hydrogen rather than the one leading to the most substituted alkene.
04Why does a polar aprotic solvent assist many SN2 reactions?
It solvates cations well without strongly surrounding the anionic nucleophile.
05How do you separate E2 from SN2 for a secondary substrate?
Compare base bulk, nucleophilicity, temperature, solvent, and accessible beta hydrogens.
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