Experiment 8: SN2 Reaction

Flashcard maker : Lily Taylor
Aim?
To see what and how factors (such as steric hindrance, nucleophilicity, and leaving groups) affect an SN2 reaction’s rate
Substitution
When another atom replaces the halide ion that leaves
Elimination
When the halide ion leaves with another atom or ion (H+ usually)
Nucleophilic substitution
A nucleophile replaces a leaving group from a carbon atom, using its lone pair of electrons to form a new bond to the carbon atom
SN1
Takes place in more than one step
SN2
Takes place in a single step, involves attacking the nucleophile and getting rid of the leaving group at the same time
What does the reaction of a tertiary amine with an organic halide produce?
A quaternary ammonium salt
What is a halide?
A group 7 gas
Factors that affect SN2 reactions
Strength of the nucleophile, the solvent, steric effects, and leaving groups
How does the strength of the nucleophile effect SN2?
Any component that has a negative charge is stronger than one that doesn’t
How does the solvent effect SN2?
Polar protic solvents slow down the substitution with their – nucleophiles. Polar Aprotic solvents speed up the substitution with their polar bonds. Non polar solvents won’t dissolve nucleophiles
How do steric effects affect SN2?
When the nucleophile closely approaches the substrate, there can be adverse effects depending on the compound’s structure
How do leaving groups effect SN2?
Depends on electronegativity, stability, and polarizability of leaving group
What procedures were used here?
Vacuum filtration
What did this experiment evaluate the effects of?
Steric hindrance on the rate of the SN2, the nucleophilicity of the amine, and the nature of the leaving group
What amines were tested?
Triethylamine, tripropylamine, ethyldiisopropylamine
What alkyl halides were tested?
Iodoethane, 1-bromopropane, 2-bromopropane
What should happen when acetone/diethyl ether/pentane, iodomethane, and amines are combined?
It should turn cloudy and form a quaternary salt
When does steric hindrance have less of an effect on the reaction rate?
When the amine’s structure has considerably less branches
When nucleophiles all have the same charge, how is nucleophilicity determined?
By periodic table trends, whichever is bigger in atomic size has ^ nucleophilicity
Bigger atomic size =
Faster rate
Lowest steric hindrance =
Fastest rate

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