ORGANIC CHEMISTRY 3540

NUCLEOPHILIC SUBSTITUTION

STEREOCHEMISTRY

KINETICS

OTHER

MECHANISM: S_N2

MECHANISM: S_N1

NUCLEOPHILIC SUBSTITUTION

SOME BIOLOGICAL REACTIONS

SOME LABORATORY REACTIONS

CH₃Br + CH₃S^-1 ---> CH₃-S-CH₃
CH₃Br + HS^-1 ---> H-S-CH₃
CH₃Br + CN^-1 ---> CH₃CN
CH₃Br + I^-1 ---> CH₃I
CH₃Br + OH^-1 ---> CH₃OH
CH₃Br + CH₃O^-1 ---> CH₃-O-CH₃
CH₃Br + CH₃CO₂^-1 ---> CH₃CO₂CH₃
CH₃Br + NH₃ ---> CH₃NH₃⁺¹

IN EACH CASE, WE CAN IDENTIFY:

• THE SUBSTRATE
• THE LEAVING GROUP
• THE ATTACKING GROUP, A NUCLEOPHILE

CALL THE REACTION

NUCLEOPHILIC SUBSTITUTION

NUCLEOPHILIC SUBSTITUTIONS ARE ONE OF THE MOST IMPORTANT REACTIONS WE WILL ENCOUNTER!

EXAMINE IN GREAT DETAIL!

R-Cl + OH^-1 ---> R-OH + Cl^-1

ONE BOND IS BROKEN, ONE BOND IS MADE.

WHICH HAPPENS WHEN?
IS R-Cl BOND BROKEN AND THEN R-OH BOND MADE?
IS R-OH BOND MADE AND THEN R-Cl BOND BROKEN?
ARE THEY MADE AND BROKEN AT THE SAME TIME?

ie, WHAT IS THE MECHANISM?

KINETICS.

RATE EQUATION

REACTION RATE = k X [RX] [OH^-1]

A SECOND ORDER REACTION

BOTH REACTANTS ARE INVOLVED IN THE RATE DETERMINING STEP!

CALL THE REACTION S_N2

• SUBSTITUTION
• NUCLEOPHILIC
• BIMOLECULAR

STEREOCHEMISTRY - WALDEN INVERSION

WHERE DID THE INVERSION OCCUR? (MALIC ACID TOO COMPLICATED TO STUDY!)

NEED A SIMPLER COMPOUND TO STUDY THE STEREOCHEMISTRY.
1-PHENYL-2-PROPANOL

HOW DO YOU DETERMINE WHERE INVERSION TOOK PLACE?

WHERE INVERSION ACTUALLY TOOK PLACE!

MECHANISM

MECHANISM ANIMATION FROM Prof. Iverson, U of TEXAS

BEFORE TS -------------------------- TS -------------------------- AFTER TS

FACTORS AFFECTING RATES OF S_N2

STERIC EFFECTS.

NATURE OF NUCLEOPHILE.

NATURE OF LEAVING GROUP.

ANOTHER SUBSTITUTION

STEREOCHEMISTRY

KINETICS

MECHANISM

TRANSITION STATE

FACTORS AFFECTING RATES OF S_N1, SUBSTITUTION, NUCLEOPHILIC, MONOMOLECULAR

NATURE OF SUBSTRATE.

NATURE OF NUCLEOPHILE.

NATURE OF LEAVING GROUP.

REARRANGEMENTS.