Characteristics of the SN1 reaction

Most substituted

For the substrate, the ______ halides will react faster (3 prime > 2 prime > 1 prime/methyl) because it forms a more stable carbocation

Carbon intermediate

Stereochemistry: A trigonal planar ____ forms, therefore a racemic mixture results (if a chiral center is formed)

1st

Kinetics: ____ order (unimolecular) aka the rate depends on [RX]

k[RX]

rate =

Neutral nucleophile

There could be more than 2 steps if there is a ______

Exothermic

Ending with a lower amount of energy

Pentacoordinate or pentavalent

The carbocation intermediate is also called a __________________ carbon

SN1 goes through a carbocation

Stereochemistry

Raceimization

Occasionally SN1 reactions do NOT undergo complete

• It is thought that the LG may still be close to its departure point and therefore blocking that side of the cation (LG may still be somewhat blocking the nucleophile)

Tertiary

______ substrates are favored

Secondary

_______ substrates could work

Methyl and primary

_______ substrates DO NOT REACT!!!!

Inductive effect

The effect on electron density in one part of the molecule that is due to electron donating groups (or electron withdrawing groups)

• The more alkyl groups, the more electron density is donated to the C+ to stabilize the carbocation’s charge

• In addition, the resonance around the C+ can also stabilize its charge (look for pi bonds and atoms with lone pairs)

Hyperconjugation

Overlap of empty p orbitals with neighboring sigma bonds that causes stabilization

Weaker base

The best LG is the _____ or the most stable species

• TsO- > I- > Br- > Cl- ~ H2O

Nucleophile

The nature of the _____ is NOT very important in the SN1 reaction because the _____ has no part in the rate-limiting (slow) step

Stable

Carbocation Rearrangements: carbocations can rearrange if it leads to a more _____ carbocation intermediate

1,2-hydride shift

Hydrogen shifts to secondary carbon to get a more stable carbocation (the tertiary without the hydrogen)

1,2-alkyl shift

An R group is shifted from a quaternary carbon to another, leaving the previously quaternary carbon as a tertiary carbon

Transition states

In an SN1 reaction, the solvent helps to stabilize the ______ and therefore the carbocation

Solvation

The carbocation is stabilized by ______

Polar protic

Use of _____ solvents are beneficial

Hydride or methyl shifts

For primary and secondary, look for ________ at neighboring C if a tertiary carbon can form