Halogen Compounds

Name $\mathbf{A}$.

There are three structural isomers of $\mathbf{A}$.

Draw the structures of these three isomers of $\mathbf{A}$.

State what the letters 'S' and 'N' represent in the abbreviation $\text{S}_\text{N}1$.

Complete the $\text{S}_\text{N}1$ mechanism for reaction 1.

Include the structure of the intermediate and all necessary charges, dipoles, lone pairs and curly arrows.

The $\text{S}_\text{N}1$ mechanism for reaction 1 is repeated using $\text{CH}_3\text{CHClCH}_2\text{CH}_3$ or $\text{CH}_3\text{CHICH}_2\text{CH}_3$ in place of the $\text{CH}_3\text{CHBrCH}_2\text{CH}_3$.

State and explain how the rates of these two reactions will compare with the rate of the original reaction using $\text{CH}_3\text{CHBrCH}_2\text{CH}_3$.

Reaction 2 uses the same reagent as reaction 1, but under different conditions.

State two differences in the conditions needed to ensure that reaction 2 is more likely to take place than reaction 1 when this reagent is added.

What is the identity of the precipitate formed when 1-chlorobutane is used?

Which of the three halogenoalkanes will produce a precipitate in about two minutes?

Use appropriate data from the Data Booklet to explain why this reaction takes place most quickly of the three.

Complete Table 5.1 for each reaction, by:

• stating the reagent and conditions used
• identifying the type of reaction that occurs.

Table 5.1

A sample of 2-iodopropane, $\text{CH}_3\text{CH(I)CH}_3$, reacts under the same conditions as reaction 1 to produce $\text{CH}_3\text{CH(OH)CH}_3$.

Explain why 2-iodopropane reacts at a faster rate than 2-bromopropane.

In step 1, 1-bromopropane reacts with $\text{CN}^-$ to form butanenitrile.

Complete Fig. 5.3 to show the mechanism for step 1. Include charges, dipoles, lone pairs of electrons and curly arrows as appropriate.

Fig. 5.3

When hot aqueous $\text{NaOH}$ is used, the $\text{C}_2\text{H}_5\text{Br}$ is hydrolysed to ethanol, $\text{C}_2\text{H}_5\text{OH}$.

Describe the mechanism of this reaction. In your answer, show any relevant charges, dipoles, lone pairs of electrons and movement of electron pairs by curly arrows.

What will be formed when $\text{C}_2\text{H}_5\text{Br}$ is reacted with $\text{NaOH}$ under different conditions?

What are the conditions used?

What type of reaction is this?

Draw the skeletal formula of the product formed when 1,4-dichlorobutane is reacted with $\text{NaOH}$ in the way you have described in (b)(ii) and (b)(iii).

Identify the nucleophile in this reaction.

Explain why this reaction is described as a substitution reaction.

Describe and explain the trend in reactivity of the different halogenoalkanes shown in this experiment.

All three halogenoalkanes tend to react via the $\text{S}_\text{N}1$ mechanism.

Explain why the $\text{S}_\text{N}1$ mechanism is favoured.

Identify a halogenoalkane which tends to react with an aqueous solution of silver nitrate and ethanol via the $\text{S}_\text{N}2$ mechanism.

Name this compound.

$(\text{C}_2\text{H}_5)_3\text{CBr}$ reacts with aqueous $\text{OH}^-$.

Complete the mechanism for this reaction including all necessary curly arrows, charges, partial charges and lone pairs.

What type of mechanism occurs in (ii)?

Give the reagents and conditions necessary for the conversion of this compound into a mixture of alkenes.

Give the name of the mechanism for the conversion in (i).

Draw the skeletal formulae of the three alkenes produced by the conversion in (i).

For each reaction, state the reagent and solvent used.

• reaction 1
  • reagent: ............................................................
  • solvent: .............................................................
• reaction 2
  • reagent: ............................................................
  • solvent: .............................................................
• reaction 3
  • reagent: ............................................................
  • solvent: .............................................................

When 1-iodobutane, $\text{CH}_3\text{CH}_2\text{CH}_2\text{CH}_2\text{I}$, is reacted under the same conditions as those used in reaction 1, butan-1-ol is formed.

What difference, if any, would there be in the rate of this reaction compared to the reaction of 1-bromobutane?

Use appropriate data from the Data Booklet to explain your answer.