Edexcel IAL Chemistry Topic 10 Halogenoalkanes, alcohols and spectra

Identify structures and reaction class first, then supply precise reagents, conditions, curly arrows or diagnostic spectral peaks required by the pathway or evidence.

Exam points

Draw nucleophilic substitution and elimination mechanisms with correct curly arrows.
Plan halogenoalkane or alcohol conversions using named reagents, conditions and products.
Interpret hydrolysis experiments, infrared absorptions and mass-spectral fragments.

Covered syllabus points

10.1—Classify reactions (including those in Unit 1) as addition, elimination, substitution, oxidation, reduction, hydrolysis or 10.2—The concept of a reaction mechanism 10.3—Heterolytic bond breaking results in species that are electrophiles or nucleophiles 10.4—The definition of the term ‘nucleophile’10.5—The link between bond polarity and the type of reaction mechanism a compound will undergo 10B: Halogenoalkanes Students will 10.6—The nomenclature of halogenoalkanes 10.7—The distinction between primary, secondary and tertiary halogenoalkanes 10.8—The reactions of halogenoalkanes with: i aqueous alkali 10.9—The mechanisms of the nucleophilic substitution reactions between primary halogenoalkanes and: i aqueous potassium hydroxide 10.10—Experimental observations and data can be used to compare the relative rates of hydrolysis of: i primary, secondary 10.11—CORE PRACTICAL 5 Investigation of the rates of hydrolysis of some halogenoalkanes 10.12—The trend in reactivity of primary, secondary and tertiary halogenoalkanes 10.13—Understand, in terms of bond enthalpy, the trend in reactivity of chloro-, bromo- and iodoalkanes 10.14—CORE PRACTICAL 6 Chlorination of 2-methylpropan-2-ol with concentrated hydrochloric acid 10.15—The nomenclature of alcohols 10.16—The distinction between primary, secondary and tertiary alcohols 10.17—The reactions of alcohols with: i oxygen in air (combustion) ii halogenating agents • PCl5 to produce chloroalkanes 10.18—Potassium dichromate(VI) in dilute sulfuric acid can oxidise: i primary alcohols to produce aldehydes (which give a positive 10.19—Understand, the following techniques in the preparation and purification of a liquid organic compound: i heating under 10.20—CORE PRACTICAL 7 The oxidation of propan-1-ol to produce propanal and propanoic acid 10.21—Interpret data from mass spectra to suggest possible structures of simple organic compounds using the m/z of the molecular 10.22—Infrared spectra, or data from infrared spectra, to deduce functional groups present in organic compounds, and predict 10.23—CORE PRACTICAL 8 Analysis of some inorganic and organic unknowns

[Maximum number: 2]

Propan-1-ol may be converted into propene.

\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{OH} \rightarrow \mathrm{CH}_{3} \mathrm{CH}=\mathrm{CH}_{2}+\mathrm{H}_{2} \mathrm{O}

(a)

Which reagent is used for this reaction?

50% sulfuric acid

ethanolic potassium hydroxide

phosphoric(V) acid

red phosphorus

[ 1 ]

(b)

The reaction is best classified as

elimination

hydrolysis

reduction

substitution

[ 1 ]

[Maximum number: 1]

Figure for Question Topic 10: Organic Chemistry: Halogenoalkanes, Alcohols and Spectra question 2 — Edexcel A-Level Chemistry AS

[Maximum number: 10]

Some reactions of a halogenoalkane are summarised in the diagram. All the reactions are of the same type and mechanism.

Figure for Question Topic 10: Organic Chemistry: Halogenoalkanes, Alcohols and Spectra question 3 — Edexcel A-Level Chemistry AS

(a)

Name the type and mechanism of these reactions.

[ 1 ]

(b)

Give the IUPAC name and the structure of compound M.

[ 2 ]

(c)

State the reagent and conditions required for Reaction 1.

[ 2 ]

(d)

An incomplete mechanism for Reaction 2 is shown.

Figure for Question (d) — Edexcel A-Level Chemistry AS

intermediate J

[ 4 ]

(i)

Complete the mechanism by adding curly arrows, and relevant dipoles and lone pairs.
(2)

[ 2 ]

An answer that shows the following

- dipole on C-Br

- curly arrow from C-Br bond to Br atom or just beyond

- lone pair on oxygen of $\mathrm{OH}^{-}$

- curly arrow from oxygen to positively charged carbon atom

All four points correct scores (2)

Any two or three points correct scores (1)

Do not award second curly arrow from negative charge

Penalise use of half-arrows once only

Ignore an extra $\mathrm{OH}^{-}$ attacking the 2-bromo-2-methylpropane molecule.

Ignore lone pair on this extra species

Ignore extra curly arrows and lone pairs

(2)

Example of mechanism

Figure for Answer to Question (i) — Edexcel A-Level Chemistry AS

(ii)

Describe how intermediate J is formed in the first step, naming the process that occurs.
(2)

[ 2 ]

(e)

The reaction of halogenoalkanes with hydroxide ions is often carried out using sodium hydroxide or potassium hydroxide.

An alternative is ‘moist silver(I) oxide’, which is prepared by adding a few drops of water to solid silver(I) oxide.

Silver(I) oxide is insoluble in water but produces sufficient hydroxide ions for the reaction.

[ 1 ]

(i)

Suggest one advantage of using silver(I) oxide rather than sodium hydroxide or potassium hydroxide.

[ 1 ]

An answer that makes reference to one of the following

- because silver(I) oxide is insoluble, it can easily be separated from the reaction mixture when reaction is complete

- because silver(I) oxide is insoluble, it can be reused

- $\ce{NaOH}$ / $\ce{KOH}$ are caustic/corrosive, or $\ce{Ag2O}$ is less corrosive than $\ce{NaOH}$ .

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Covered syllabus points

Topic 10: Organic Chemistry: Halogenoalkanes, Alcohols and Spectra question 1

Question (a)

Question (b)

Topic 10: Organic Chemistry: Halogenoalkanes, Alcohols and Spectra question 2

Topic 10: Organic Chemistry: Halogenoalkanes, Alcohols and Spectra question 3

Question (a)

Question (b)

Question (c)

Question (d)

Question (i)

Question (ii)

Question (e)

Question (i)