Hydrocarbons Flashcards
Alkanes, Alkenes, Alcohols and Esters
Define homologous series
Organic compounds with the same functional group
Define hydrocarbon
A compound made of carbon and hydrogen bonds only
Describe alkanes.
General formula: CnH2n+2
Saturated - contains only single bonds
Reactions - very unreactive as they are saturated and non-polar
Describe the reactions of alkanes.
- Combustion
Complete - Alkane + O2 -> CO2 + H2O
Incomplete - Alkane + O2 -> CO + H2O
- Free-radical substitution
Alkane + Halogen (Cl2, Br2, I2)
Condition: UV Light
Mechanism:
2.1. Initiation
Formation of free-radical
Requires UV Light
Homolytic fission
2.2. Propagation
Formation of organic free radical
2.3. Termination
Addition of 2 free radicals
- Cracking
Breaking up of a large chain molecule into smaller, more useful chains
Using heat and Al2O3
Products: Alkenes, Alkanes and Hydrogen
Describe alkenes.
General formula: CnH2n
Empirical formula: CH2
Unsaturated
Describe reactions of alkenes.
- Electrophilic addition
Electrophile - species attracted to areas of negative charge i.e. electron deficient
Heterolytic fission
1.1. Addition of H2
Reagent - Hydrogen
Conditions - Heat, Nickel/Platinum catalyst
Product - Alkane
1.2. Addition of Hydrogen Halide
Reagent - HBr/HCl/HI etc.
Conditions - RTP (room temperature and pressure)
Product - Haloalkane
1.3. Addition of water
Reagent - Steam
Conditions - Heat, H3PO4 catalyst
Product - Alcohol
- Oxidation of alkenes
Oxidising agent - KMnO4, H+
Colour change - purple -> colourless/pink
Conditions determine product:
2.1. Cold, dilute KMnO4 solution
Forms a diol
2.2. Hot, concentrated KMnO4 solution
Cleavage reaction
Reagents: Acid + KMnO4
Conditions: Hot and concentrated
Forms a ketone or an aldehyde or CO2 + H2O
Describe alcohols.
Functional group: -OH
Classification:
Primary - carbon atom attached to OH has only 1 carbon atom attached to it
Secondary - carbon atom attached to OH has 2 carbon atoms attached to it
Tertiary - carbon atom attached to OH has 3 carbon atoms attached to it
Describe the reactions of alcohols
- Combustion
Products CO2 + H2O - Oxidation
Oxidising agent - K2Cr2O7, H+ / KMnO4
Colour change: Orange to green
2 Types of oxidation reactions:
2.1. Partial oxidation - only in primary alcohols
Forms aldehyde - distillation necessary to collect aldehyde /collect product
Conditions: Heat, Distilled off
2.2. Complete Oxidation
If primary alcohol - forms carboxylic acid
If secondary alcohol - forms ketone
If tertiary alcohol - does not oxidise (stays orange/ no colour change)
- Nucleophilic Substitution
3.1. Reaction with HCl / HBr -> Haloalkane
3.2. Reaction with PCl3 or PCl5 to produce chloroalkanes
3.3. Reaction with red phosphorus and I2 / Br2 -> Haloalkane
3.4. Reaction with thionylchloride (SOCl2) to produce chloroalkane
3.5. Reaction with sodium to form sodium alkoxide
Observations: Colourless gas released
Makes a pop sound with a burning splint
- Elimination
Conditions:
Heat with an acid catalyst, either H2SO4 or H3PO4
Heat with Al2O3
Describe esterification.
Alcohol + Carboxylic acid -> Salt + Water
Conditions:
Heat with H2SO4 catalyst
Uses: Solvents, Perfumes and Flavourants
Describe the reactions of esters.
- Hydrolysis of esters
1.1. Acid hydrolysis
1.2. Alkali hydrolysis
Describe the formation of alcohols.
- Fermentation
Starting material - plant-based
Temperature < 40 degrees C to avoid enzymes being denatured
Enzyme (biological catalyst) - yeast
Yeast is destroyed when alcohol concentration gets too high
Slow process
Only ethanol can be made - Hydration of Alkenes
Alkene + Water -> Alcohol
Reaction conditions:
Addition of H2O to an alkene in the presence of a strong acid
Describe the physical properties of alcohols.
Boiling point of an alcohol is always higher than the alkene with the same number of carbon atoms, due to the presence of hydrogen bonding in alcohols.
Boiling points increase as the number of carbon atoms increase
