Make-up Lab 3

N-heptane + Bromine water observation

2 phases - Upper phases:

a) Darker yellow, b) polar yellow solution

Why do we wrap one test tube in aluminum foil?

To block out UV light and prevent the reaction

What happens when bromine reacts with an alkane in UV light?

Alkane reacts with bromine via free radical substitution

Tertiary-amyl alcohol + Bromine water

Observation: Exposed to sunlight - turns pale + further colorless

only alkyl group reacts here

Reaction mechanism of bromine water + alkene

Electrophilic addition

Role of UV light?

To break br-br bonds to form free radicals

Purpose of bromine water

To test for unsaturation (presence of double bonds)

Observation indicates this presence?

Bromine water turns from orange/brown to colorless

Why bromine water delocalizes with alkenes but not alkanes?

Because of the presence of the pi bond in alkenes; alkanes don’t have pi bonds only sigma bonds.

N-heptane + Acidified KMnO4

No reaction, because only contains non-reactive sigma bonds.

1-heptene + Acidified KMnO4

Hexanoic acid forms/ (Heptane-1,2-diol)

Presence of pi bonds, KMnO4 is strong oxidizing agent and attacks this pi bond.

Maleic acid + Acidified KMnO4

Fumaric acid forms

Purple - colorless solution

KMnO4 is strong oxidizing agent, attacks pi bond present in the acid, thus oxidizing double bond.

Calcium carbide + H20 + 2-propanol

Reaction mechanism = Electrophilic addition

Observation - Turns colorless

1-bromopropane + ethanolic NaOH (heat + HNO3 + AgNO3)

Reaction mechanism = Nucleophilic substitution
Observation - Formation of a white precipitate

Why is nitric acid added?

To eliminate excess NaOH because AgNO3 + NaOH will form a brown, silver oxide so no color change can be seen.

2-propanol + Lugol solution + NaOH

Forms Iodoform

Observation: Pale yellow - colorless

RM - Nucleophilic substitution

Steps and what happens?

2 propanol is oxidized propanone (acetone)

Formation of enolate ion

Iodine reacts with this ion to form iodoform ketone

Formation of yellow precipitate = Iodoform + Na acetate

Ter-butyl alcohol + HCl (concentrated)

Chloroalkanes do not mix with water but t-butanol does.

observation = pale, milky, colorless

RM - Sn

Why does t-butanol react with water but chloroalkanes do not?

Because water is too weak for a nucleophilic substitution reaction and chloroalkanes are non-polar, whereas t-butanol is polar, due to the presence of the OH group. It reacts very quickly and can the compound to form a tertiary carbocation.