S3.2 Organics - Functional Groups

List the functional group, molecular formula and general formula of alcohols

• Functional group: hydroxyl group (-OH)

• molecular formula: C_nH_2n+1OH

• general formula is R-OH, where R represents an alkyl group

With reference to intermolecular forces and chain length, explain the solubility of alcohols

• alcohols can form hydrogen bonds due to the covalent bonding between O and H

  • therefore, can dissolve in water

• however, as chain length inc. solubility dec.

  • the hydrophobic (nonpolar) nature of the alkyl group (carbon chain) becomes more significant, overpowering hydrophilic interactions (H-bonding)

    • Longer chains increase van der Waals forces, making it harder for alcohols to dissolve in water.

What is the difference between primary and secondary alchohols

• Primary Alcohols: -OH group on a carbon bonded to only one other carbon (or none in methanol).

• Secondary Alcohols: -OH group on a carbon bonded to two other carbons.

How can primary and secondary alcohols be identified chemically? (hint: colour change)

• In a reaction w/ acidified potassium dichromate (VI) → colour change from orange to green happens (CAN ALSO BE SEEN w/ Aldehydes)

List and explain the 3 different main reactions that happen with alcohols

• Combustion

  • alcohol + oxygen → carbon dioxide + water

• Oxidation

  • W/ heat, acidic conditions & immediate distillation | primary alcohol + [O} → aldehyde

  • W/ excess [O], acidic conditions & reflux| primary alcohol + [O] → aldehyde → carboxylic acid

  • W/ acidic conditions & reflux |

    • secondary alcohol + [O] → ketone

  • TERTIARY ALCOHOLS CANNOT be oxides

• Elimination

  • water can be eliminated to form alkenes

  • called dehydration - when alcohols are heated w/ sulfuric acid catalyst

  • alcohol → (H+ catalyst/ heat) → alkene + water

Explain the 3 different Oxidation reactions with alcohols

• Oxidation

  • W/ heat, acidic conditions & immediate distillation | primary alcohol + [O} → aldehyde

  • W/ excess [O], acidic conditions & reflux| primary alcohol + [O] → aldehyde → carboxylic acid

  • W/ acidic conditions & reflux |

    • secondary alcohol + [O] → ketone

  • TERTIARY ALCOHOLS CANNOT be oxides

Explain two ways Ethanol can be produced

1. Fermentation of glucose (requiring microbe yeast and 30-40˚c temp)

2. Hydration of ethene in presence of strong acid catalyst (in high temp and pressures, requiring high energy)

List the functional group, molecular formula and general formula of aldehydes

C=O group (called carbonyl) bonded to H atom

CH=O

What two reagents can be used to identify aldehydes

1. Fehling’s solution - blue solution, forms red precipitate with aldehydes

2. Tollen’s reagent - colourless solution, forming silver mirror with aldehydes. aldehydes can be attacked by nucleophiles (DONATES e-)

Explain the 2 main reactions involving aldehydes

• Oxidation - aldehydes readily oxidise to carboxylic acids

  • aldehyde (CO) + [O] → carboxylic acids (COOH)

• Nucleophilic Addition -

  • Reduction reaction to form primary alcohols (e.g. NaBH₄) | aldehyde + 2[H] → primary alchohol

  • with KCN, followed by dilute