Chapter 9: Substitution Reactions Flashcards
What is this type of substitution reaction?
SN2
What is this type of substitution reaction?
SN1
The rate of a SN2 reaction is dependent on what?
the concentrations of nucleophiles and electrophiles
The rate of a SN1 reaction is dependent on what?
the loss of a leaving group
Primary Substrate
Secondary Substrate
Benzylic Group (Bn)
Allylic Group
Tertiary Substrate
What carbocations are most stable and why?
tertiary
the 3 alkyl groups stabilize the charge
What substrates do SN2 reactions favor?
primary and secondary substrates
nucleophiles can’t attack tertiary substrates because of steric hinderance
What substrates do SN1 reactions favor?
tertiary substrates
no steric hinderance because the nucleophilic attack doesn’t happen in the first step of the reaction. SN1 reactions also depend on the stability of the carbocation formed from loss of LG and tertiary substrates are more stabilized
Why do these molecules favor SN1 reactions?
the carbocation formed from the loss of LG can be stabilized through resonance
What type of reaction is dependent on the nucleophile and why?
SN2 reactions
the nucleophilic attack happens in the first step of the reaction
What makes a strong nucleophile?
a negative charge and polarizability (related to size of atom and number of valence electrons)
Strong nucleophiles
favor SN2
Weak nucleophiles
favor SN1
What reaction is more sensitive to the LG and why?
SN1
the loss of a LG is the rate determining step in SN1 reactions
What makes a good leaving group?
good LG are conjugate bases of strong acids (hint: strong acids have weak conjugate bases)
What makes a strong acid?
ARIO
Atom
Resonance
Induction
Orbitals
Good LG
Bad LG
tosylate (TsO)
mesylate (MsO)
triflate (TfO)
What is a polar aprotic solution?
no H+ on electronegative atoms
What type of reaction do polar aprotic solutions favor?
SN2
Dimethylsulfoxide (DMSO)
Acetone
Dimethylformamide (DMF)
Why do polar aprotic solutions favor SN2 reactions?
A nucleophile dissolved in a polar aprotic solution won’t have a solvent shell around the negative charges to prevent a nucleophilic attack (SN2 dependent more on the NA)
