Study guide: Alcohols Haloalkanes and Analysis

📋 Course Outline

1. Alcohol Structure and Properties
2. Alcohol Reactions and Oxidation
3. Haloalkane Reactivity
4. Nucleophilic Substitution and Ozone
5. Organic Preparation Techniques
6. Synthetic Routes and Identification
7. Infrared Spectroscopy
8. Mass Spectrometry

📖 1. Alcohol Structure and Properties

🔑 Key Concepts & Definitions

• Alcohols: Organic compounds containing an –OH group with the general formula CnH2n+1OH.

★ Must-know

📌 Alcohols are primary, secondary, or tertiary depending on the position of the hydroxyl group.

• Alcohols are polar and water soluble because the electronegative oxygen atom can hydrogen-bond with water molecules.

Further detail

📌 Alcohols are less volatile than alkanes because alcohols have hydrogen bonds and van der Waals forces, whereas alkanes have only van der Waals forces.

💡 Memory Hook

Alcohols hydrogen-bond with water, whereas alkanes only experience van der Waals forces.

📖 2. Alcohol Reactions and Oxidation

★ Must-know

• Combustion of an alcohol in air produces carbon dioxide and water while releasing substantial energy.

• Alcohols undergo nucleophilic substitution with halogenating agents in which the –OH group is replaced by a halogen to form a haloalkane.

• Primary alcohols oxidise to aldehydes and then carboxylic acids, while secondary alcohols oxidise to ketones and tertiary alcohols are not easily oxidised.

Further detail

• Phosphorus pentachloride tests for alcohols because the reaction produces white steamy fumes that turn damp blue litmus paper red.

• Acidified potassium dichromate(VI) changes from orange to green because chromium is reduced while the alcohol is oxidised.

💡 Memory Hook

Primary alcohol → aldehyde → carboxylic acid; secondary alcohol → ketone.

📖 3. Haloalkane Reactivity

🔑 Key Concepts & Definitions

• Haloalkanes: Organic compounds containing polar carbon–halogen bonds because halogens are more electronegative than carbon.

★ Must-know

📌 Haloalkane reactivity increases down the halogen group because carbon–halogen bond enthalpy decreases as the halogen relative molecular mass increases.

• Aqueous sodium or potassium hydroxide converts haloalkanes to alcohols by nucleophilic substitution, whereas ethanolic potassium hydroxide converts them to alkenes by elimination.

Further detail

📌 Haloalkanes are classified as primary, secondary, or tertiary according to the position of the halogen within the carbon chain.

💡 Memory Hook

Down-group bond weakening → faster haloalkane reaction.

📖 4. Nucleophilic Substitution and Ozone

★ Must-know

• In nucleophilic substitution, a nucleophile donates an electron pair to the electron-deficient carbon attached to the halogen while the carbon–halogen bond breaks.

• In the silver nitrate hydrolysis test, chloride gives a white AgCl precipitate, bromide gives a cream AgBr precipitate, and iodide gives a yellow AgI precipitate.

• CFCs undergo UV photolysis to form chlorine radicals, which catalyse ozone breakdown through regeneration of the chlorine radical.

Further detail

• Common nucleophiles include:
  • CN⁻
  • NH3
  • OH⁻

📐 Formula - The overall reaction for catalytic ozone breakdown is $2O_3 \rightarrow 3O_2$.

💡 Memory Hook

CFC photolysis → chlorine radicals → catalytic ozone breakdown.

📖 5. Organic Preparation Techniques

★ Must-know

• Reflux continually heats a reaction while a condenser returns vapours to the flask, preventing product loss and allowing oxidation to proceed to carboxylic acids.

• Distillation separates liquids with different boiling points because the liquid with the lower boiling point evaporates first, condenses, and is collected.

Further detail

• A separating funnel separates immiscible liquids into layers and allows the denser bottom layer to be collected before the less dense layer.

• Anhydrous magnesium sulfate or calcium chloride absorbs water to dry and purify an organic compound.

💡 Memory Hook

Reflux retains vapours for reaction, whereas distillation separates liquids.

📖 6. Synthetic Routes and Identification

★ Must-know

• 🔄 A multi-stage synthesis proceeds through:

  1. a starting reactant
  2. one or more intermediates
  3. the desired product

• Functional-group tests include: bromine water for unsaturation, acidified potassium dichromate(VI) for primary and secondary alcohols, Tollens’ reagent for aldehydes, aqueous silver nitrate with ethanol for haloalkanes

Further detail

📌 More sustainable synthetic routes favour addition reactions, renewable and safer reagents, less harmful or useful by-products, and energy-efficient safe conditions.

• Boiling-point determination assesses purity because a pure substance boils close to its databook value, whereas an impure sample changes phase over a temperature range.

💡 Memory Hook

Reactant → intermediate → product.

📖 7. Infrared Spectroscopy

🔑 Key Concepts & Definitions

• Infrared spectroscopy: Identifies functional groups by measuring the absorption of infrared radiation by vibrating covalent bonds.

★ Must-know

• The characteristic alcohol O–H absorption is a broad peak at 3230–3550 cm⁻¹, whereas the carboxylic-acid O–H absorption occurs at 2500–3300 cm⁻¹ and overlaps the C–H region.

• C=C absorbs sharply at 1620–1680 cm⁻¹ and C=O absorbs sharply at 1680–1750 cm⁻¹.

Further detail

• The fingerprint region from 500–1500 cm⁻¹ contains unique small differences for each molecular species and can identify a compound.

💡 Memory Hook

A molecule’s unique fingerprint appears in the 500–1500 cm⁻¹ region.

📖 8. Mass Spectrometry

🔑 Key Concepts & Definitions

• Mass spectrometry: Identifies molecules and determines relative molecular mass by measuring ions according to their mass-to-charge ratios.

★ Must-know

• 🔄 Time-of-flight mass spectrometry involves:

  1. ionisation
  2. acceleration
  3. ion drift
  4. detection
  5. analysis

• The molecular ion peak is the peak furthest to the right and its m/z value can be used to calculate the relative molecular mass.

Further detail

• A small M+1 peak can arise from the small proportion of carbon-13 isotopes present in an organic compound.

• Fragmentation produces a charged fragment ion and an uncharged radical, so only the fragment ion appears as a peak in the mass spectrum.

💡 Memory Hook

Ionisation → acceleration → ion drift → detection → analysis.

📊 Synthesis Tables

Alcohol oxidation products

Starting alcohol	Product	Conditions
Primary alcohol	Aldehyde, then carboxylic acid	Acidified potassium dichromate(VI); distillation or reflux
Secondary alcohol	Ketone	Acidified potassium dichromate(VI)
Tertiary alcohol	Not easily oxidised	—