3- SN1 Flashcards
explain the two step process of sn1 reactions
1st step dissociating the leaving group → the carbocation is now sp2 AND there is space for the nucleophile to attack
second step is the nucleophile attacking
what is the rds in sn1 reactions? state the fast and slow reactions
Formation of the carbocation intermediate (slow) RATE-DETERMINING STEP
Reaction between the nucleophile and the intermediate (fast)
explain the energy diagram for sn1 reactions
RDS requires more energy, higher peak
reacts at beginning, the intermediate (between two peaks- T states) is the carbocation
first step only involves the substrate, therefore the nucleophile is not included for the RDS
what is the kinetic equation for sn1 reactions? what order?
rate=k[R-X]
first order reactions
why are sn1 reactions unimolecular?
Rate depends only on the concentration of the electrophile:
explain the stereochemistry of sn1 reactions
Carbocations are sp2 hybridized trigonal planar (flat).
Nucleophile are free to approach either side of the carbocation (50%)
SN1 starts with dissociation and by doing so, you go from an SP3 to an SP2
SP2 means you have an open top and open bottom for the nucleophile to attack
why is there a mixture in the stereochemistry of sn1 reactions?
Results: mixture of both enantiomers pf chiral carbon.
SP2 means you have an open top and open bottom for the nucleophile to attack
what do sn1 reactions depend on?
electrophile
what two things can carbocations be stabilized by?
Hyperconjugation
Charge delocalization
explain what hyperconjugation is, and explain stability in relation to it
- Partial overlap between shared σ bond electrons and carbocation p orbital.
- tertiary is more stable than secondary (because of sigma bonds next to the carbocation that are partially sharing their electrons with the empty orbital)
- the more sigma bonds sharing electrons, the more stable the carbocation.
what do more alkyl groups mean for the stability for the carbocation
More alkyl groups, more stable is the carbocation.
more possible sigma bonds to share their electrons with the empty p orbital
3º > 2º > 1º
explain the carbocation being stabilized by charge delocalization. what does allylic mean, too
Stabilized by pi bond electrons or heteroatom’s lone pair
allylic is when you have a carbon alpha right next to a pi bond
because there is a pi bond, there is a possibility of creating a primary carbocation that can be stabilized
what are carbon rearrangements?
Rearrangements are common in SN1 reactions
Rearrangements occur when a more stable carbocation can be formed.
list the increasing stability of carbocations (5 columns)
column one: methyl two: 1º alkyl three: 2º alkyl, 1º allylic, 1º benzylic four: 3º alkyl, 2ºallylic, 2º benzylic five (best): 3º, 3º benzylic
explain the 1,2 hydride shift
- once you make the carbocation, there is a possibility for the carbocation to go through a rearrangement into going into a more stable form
- [1,2] hydride means a hydrogen is moving from 1 carbon to neighbouring carbon
- check to see which carbon is a better choice (which one will be able to donate its electrons to the carbocation)
- always want to form something more stable
