Ch 7.1

what are the products of an Sn1 rxn?

racemization

what are the products of an Sn2 reaction?

inversion

what is the number of humps in a diagram equal to?

the steps in the mechanism

if there is steric hinderance at the electrophilic site, what rxn does that favor?

Sn1

what reaction has a more stable carbocation?

Sn1

what factors affect the stability of carbocations?

induction and resonance

what do methyl and primary substrates favor?

Sn2

what do tertiary substrates favor?

Sn1

what can secondary substrates and allylic and benzylic substrates react via?

either mechanism

what does an Sn2 process depend on?

the concentration of the nucleophile

• strong nucleophile will speed up rate

• weak nucleophile will slow it down

what does an Sn1 process not depend on?

nucelophile

a weak nucleophile disfavors Sn2, which allows _____ to complete sucessfully>

Sn1

what makes a nucleophile strong or weak>

stability, and sterics

what tend to be good nucleophiles

sterically hindered negatively charged molecules

what atoms can be strong nucleophiles when neutral?

larger atoms

• has many electrons distant from the nucleus

• electron density can be unevenly distributed

what are both Sn1 and SN2 rxs sensitive to?

identity of the leaving group

• if leaving group is bad then neither substitution can occur

what make a leaving group good or bad?

stability once it has left with a pair of electrons

• induction, resonance, solvation

whats a general rule of leaving groups?

good leaving groups are conjugate bases of strong acids

what are the most common leaving groups?

halides and sufonate ions

• iodine best out of halides

• triflate best out of sulfonate

what is the most commonly used sulfonate ion?

tosylate

• abbreviated as OTs

what does the polar solvent surround?

each species in the mechanism, including transition statew

what should the solvent do in Sn2?

facilitate the collision between the nucleophile and the electrophile

• more reactive

what can the solvent affect?

can make the nucleophile more stable and less reactive and the stability of the LG

what solvents promote Sn2 rxns?

polar aprotic

what is a polar aprotic solvent?

contain no hydrogen bonded directly to an electronegative atom

• stabilize the counter ion of the nucleophile

• will not stabilize anions (nucleophile)

  • leaving nucleophile mostly naked

what happens with polar aprotic in Sn2?

nucleophile is less stable and starts with high potential energy

• the activation energy will be lower and the reaction faster

how to promote Sn1 reaction?

polar, protic solvent

what is polar protic solvent?

contain at least one hydrogen atom directly connected to an electronegative atom

• will hydrogen bond with nucleophile

• stabilize it, while the leaving group leaves first

what does a polar proticc solvent do in a Sn1 rxn?

stabilize the full and partial charges that form during the Sn1 mechanism

• lowers the energy of the TS and the intermediates

what are some polar aprotic solvents?

DMSO, Acentonitrile, DMF, HMPA

what are some polar protic solvents?

Water, methanol, acetic acid, ammonia, and ethanol

what is the alpha position of a halide?

carbon directly connected to halogen

what is the beta position?

the carbon atoms connected to the alpha position