What is an alkyl halide?
An organic compound in which a halogen (Cl
Why are alkyl halides important in organic synthesis?
They are starting materials for many functional groups via nucleophilic substitution reactions.
What is a nucleophile?
A species with an unshared pair of electrons that can attack an electrophilic center.
What is a leaving group?
An atom or group that can depart with a pair of electrons during a substitution reaction
Compare S_N1 and S_N2 mechanisms.
S_N1: two-step
What is the rate-determining step of an S_N1 reaction?
Formation of the carbocation from the alkyl halide.
How does carbocation stability affect S_N1 reactions?
More stable carbocations (tertiary
Describe the stereochemistry of S_N1 reactions.
Racemization occurs because the planar carbocation allows nucleophile attack on either face.
Describe the stereochemistry of S_N2 reactions.
Inversion of configuration occurs due to backside attack by the nucleophile.
Which halide is the best leaving group?
Iodide (I-) > bromide (Br-) > chloride (Cl-) > fluoride (F-).
How does steric hindrance affect S_N2 reactions?
Greater steric hindrance slows S_N2 reactions; tertiary halides rarely react via S_N2.
How do solvents affect S_N1 reactions?
Polar protic solvents stabilize the carbocation and transition state
How do solvents affect S_N2 reactions?
Polar aprotic solvents (e.g.
What is the effect of temperature on substitution reactions?
Higher temperature increases kinetic energy
Why do vinylic and aryl halides rarely undergo S_N1 or S_N2?
Vinylic/aryl carbocations are unstable; nearby π electrons repel nucleophiles.
What is the general reaction for an S_N2 reaction with sodium iodide?
R-X + NaI → R-I + NaX in acetone
Why is acetone used in S_N2 reactions?
Polar aprotic solvent that dissolves NaI but does not favor halide ion ionization
What is the general reaction for an S_N1 reaction with silver nitrate?
R-X + AgNO3 (ethanolic) → R+ + AgX precipitate
Why is ethanolic AgNO3 used in S_N1 reactions?
Ethanol favors halide ionization
List examples of alkyl halides used in this lab.
1-bromobutane
How much halide is used per reaction tube?
0.1 mL or 100 mg per 3-mL tube or vial.
How much sodium iodide solution is added for S_N2 tests?
1 mL of 18% NaI in acetone
How much ethanolic AgNO3 solution is added for S_N1 tests?
1 mL of 1% ethanolic AgNO3
What indicates an S_N2 reaction has occurred?
Formation of NaX precipitate in acetone; faster with unhindered primary halides.
