Halogenoalkanes

Define methyl with respect to the classification of halogenoalkanes

The carbon to which the halogen-group is attached to has no R-groups

Define primary with respect to the classification of halogenoalkanes

The carbon to which the halogen-group is attached to has only 1 R-group

Define secondary with respect to the classification of halogenoalkanes

The carbon to which the halogen-group is attached to has two R-groups

Define teritiary with respect to the classification of halogenoalkanes

The carbon to which the halogen-group is attached to has three R-groups

What is a nucleophile

An electron pair donor

What is needed for an halogenoalkane to undergo a substitution reaction

A nucleophile

What is conditions are necessary for the nucleophilic substitution of a halogenoalkane with OH- ions (NaOH or KOH)

• heated

• Under reflux

• In aqueous solution

Outline the mechanism for the reaction between bromoethane and NaOH(aq)

State the role of the hydroxide ion here

Nucleophile/electron donor

What is this: CN-

A cyanide ion

What are the conditions necessary for the nucleophilic substitution of CN- with a halogenoalkane (KCN)

• heated

• Under reflux

• In ethanol/water mix

Outline the mechanism for the reaction between bomoethaen and KCN in ethanol/water solution

What is the IUPAC name for the product formed here

Propanenitrile

What are the conditions necessary for the nucleophilic substitution of NH3 with a halogenoalkane

• Heat

• In sealed tube

• In ethanol

Why is ethanol used as a solvent during the nucleophilic substitution of ammonia

• It minimised the chances of hydrolysis of the halogenoalkane to form an alcohol and increases miscibility

• Ammonia is slightly soluble in ethanol

Outline the mechanism for the reaction between bromoethane and ammonia

Give the IUPAC name for the organic product formed here

Ethanamine

Explain why the amine produced here can lead to the production of (C2H5)2NH and (C2H5)3N

Amine produced still has a lone pair of electrons on nitrogen atom so can still act as a nucleophile and can facilitate further substitution of halogenoalkanes to form secondary or tertiary amines

Describe and explain the test for halogenoalkanes

• add ethanol and aqueous silver nitrate

• Warm mixture gently

• Water acts as a nucleophile and substitutes halogenoalkanes

• Halide ions formed forms precipitate of silver halide in presence of Ag+(aq) ions

• CH3X + H2O → HX + CH3OH

Why do we need to add ethanol in the test for halogenoalkanes

It acts as a solvent to dissolve both the halogenoalkane and water so they can mix fully and react together

Why is 1-iodobutane more reactive than 1-chlorobutane

C-I bonds are longer and have lower bond enthalpy so less energy required to break C-I bonds

What are the conditions necessary for the elimination reaction of halogenoalkanes

• heated to a boil

• Under reflux

• With potassium hydroxide

• In ethanol

• With NaOH or KOH

What is given off in an elimination reaction of halogenoalkanes

Water, an alkene and a halide ion

Outline the mechanism for the elimination reaction between OH- ions and chloroethane

What is the OH- ion working as here

A base

What class of halogenoalkane is needed for nucleophilic substitution

Primary or secondary (Tertiary too stable?)

What class of halogenoalkane is needed for elimination

Secondary or tertiary

What temperatures are necessary for nucleophilic substitution

Relatively low

What temperatures are needed for elimination

Relatively higher

What solvent is used for substitution

Aqueous

What solvent is used for elimination

Ethanol