U4 AOS1: Organic Compounds Flashcards
Structure, nomenclature and reactions
Organic molecules
- Molecules of carbon compounds
- C is almost always associated with H
- C forms four strong covalent bonds
- Can be naturally or synthetically produced
Polar vs non-polar
- Polar – uneven electron distribution
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Non-polar - even electron distribution
- C–H bond is non-polar (low electronegative difference)
NOTE: The longer the hydrocarbon chain, the more non-polar it becomes (effect of functional group on the molecule lessens).
Saturated vs unsaturated molecules
- Saturated – contains only single C–C bonds (alkanes)
- Unsaturated – contains 1/more double or triple C–C bonds (alkenes or alkynes)
Bond energy and strength
- Energy – quantity of energy required to break 1 mole of covalent bonds in the gaseous state
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Strength – bond energy is a measure of bond strenth
- The higher the bond energy, the stronger the bond
Degree of unsaturation
- How many double bonds/ring structures a molecule has
- Every time a molecule forms a double bond or a ring, there will be two fewer hydrogen atoms present
Isomers
- Molecules with the same number and type of atoms (same molecular formula), arranged in different ways
- Can have different physical and chemical properties
Alkanes
- General formula: CnH2n+2 (n = no. carbons)
- Have only single C–C bonds (saturated)
- Can form isomers when they have 4/more carbons (can form branches)
Cyclohexane
- General formula: CnH2n
- Alkane arranged in a closed ring (no terminal carbon)
- Saturated molecule
NOTE: A terminal carbon is the carbon at the end of the carbon parent chain.
Alkenes
- General formula: CnH2n
- Have at least one C–C double bond (unsaturated)
- More reactive than alkanes
- Double bond causes a ‘kink’ in the carbon chain, decreasing BP due to lower dispersion forces
- Can form structural isomers when they have 4/more carbons atoms (location of C–C double bond changes)
Benzene
- Molecular formula: C₆H₆
- Unsaturated cyclic compound with 6 carbons
- Each C is bonded to one H and two adjacent C
- Very stable structure
- Have a circle in the middle for skeletal formula
Haloalkanes
- Alkane-based compounds whith 1/more halogen atoms bonded to the carbon chain
- E.g. chlorine, bromine, fluorine, and iodine
Primary amines
- Contain an amino (−NH₂) functional group
Primary amides
-
Amide (−CONH₂) functional group on a terminal carbon
- Carbonyl group (C=O) bonded to a nitrogen atom (NH₂)
Alcohol
- Contain a hydroxyl (–OH) functional group
- Primary: C bonded to -OH is bonded to 1 alkyl group
- Secondary: C bonded to -OH is bonded to 2 alkyl groups
-
Tertiary: C bonded to -OH is bonded to 3 alkyl groups (requires branching at the C attached to the –OH)
- Very stable structure
NOTE: O−H bonds are highly polar (negative charge shifts towards O).
Aldehydes
- Aldehyde (–CHO) functional group on a terminal carbon
- C attached to the aldehyde group is always C number 1
Ketones
- Carbonyl (C=O) group within the C chain (never at the end)
- Number is added before the suffix (-one) to indicate which carbon the carbonyl group is attached to
Carboxylic acids
-
Carboxyl (−COOH) functional group on a terminal carbon
- Made up of a hydroxyl (−OH) and carbonyl (C=O) group
- Able to donate H+ to a solution, so can act as a weak acid
Non-branched esters
- Ester (−COOC−) functional group within the carbon chain
- Form when alcohols react with carboxylic acids
- Naming: [alcohol part] –yl + [carboxylic acid part] –oate
Naming organic compounds
- Name longest carbon chain
- Single/double bonds
- Name + locate functional groups
- Only 1 suffix (group with the highest priority)
- Prefixes alphabetical (lower priority groups)
- Commas separate numbers
- Hyphens separate numbers from words
- No space between words
Parent chain prefixes
- 1 – Meth
- 2 – Eth
- 3 – Prop
- 4 – But
- 5 – Pent
- 6 – Hex
- 7 – Hept
- 8 – Oct
Prefixes when there are multiple of the same alkyl side chain
- 2 – di
- 3 – tri
- 4 – tetra
Intermolecular vs intramolecular forces
-
Intermolecular – bonds between molecules
- Dispersion (NP)
- Dipole-dipole (P)
- Hydrogen bonding
- Intramolecular – bonds within molecules
Dispersion forces
- Weakest type of intermolecular force
- Non-polar
- Present in all molecules
- Stronger in molecules that are
- Longer (more electrons and greater surface area)
- Regularly shaped (less kinks)
- Saturated (can pack together more tightly)
NOTE: Alkanes and alkenes only have dispersion forces.
Dipole-dipole
- Only occur in polar molecules
- Increase boiling point, melting point and viscosity
Hydrogen bonding
- Type of permanent dipole-dipole attraction (very strong)
- Occurs when H is bonded to nitrogen, oxygen or fluorine
- Increase boiling point, melting point and viscosity
NOTE: Hydrogen bonds are not chemical bonds. They are forces of electrostatic attraction between adjacent molecules.
Melting and boiling point of alkanes and alkenes
- Low as they only have weak dispersion forces
- The longer the carbon chain, the greater the strength of dispersion forces between molecules which ↑ MP & BP
NOTE: As melting and boiling points increase, so does viscosity.
Viscosity
- Resistance to flow
- Increases as the forces of attraction between molecules increase (therefore, longer molecules have greater viscosity)
- Decreases as temp increases as molecules move more quickly (higher kinetic energy available to overcome forces)
Substitution reactions
Occurs when an atom or functional group in a molecule is replaced by another atom or group.
-
Between an alkane and halogen
- E.g. bromine
- UV light or heat is required to initiate the reaction
- Produces a haloalkane
-
Between a haloalkane and an alkali
- E.g. sodium hydroxide (NaOH)
- Produces an alacohol
-
Between a haloalkane and ammonia (NH3)
- No catalyst is required
- Produces a primary amine
-
Between a primary alcohol and ammonia
- Requires heat and alumina (Al₂O₃) as a catalyst
- Produces a primary amine
NOTE: Ammonia only reacts with haloalkanes NOT alkanes.
Addition reactions
Occurs when a small molecule is added to the double bond of an alkene. 2 reactants combine to form 1 product.
-
Hydrogenation: alkene + hydrogen
- Requires a metal catalyst (e.g. nickel)
- Hydrogen is oxidised and carbon is reduced (redox)
- Produces an alkane
-
Halogenation: alkene + halogen
- Can proceed at room temp w/o a catalyst
- Produces a haloalkane
- Can be used to test for double bonds
-
Hydration: alkene + water vapour
- Requires heat, pressure and concentrated phosphoric acid (H₃PO₄) as a catalyst
- Produces an alcohol
-
Polymerisation: alkene monomers
- Produces a polymer (large molecule)
Esterification reactions
Type of condensation reaction where a carboxylic acid and an alcohol react to produce a water molecule and an ester.
-
Carboxylic acid + primary alcohol
- Reversible reaction
- Requires heat and concentrated sulphuric acid (H₂SO₄(l)) as a catalyst to speed up the reaction
- Produces an ester
Hydrolysis reactions
Water is a reactant and is used to break the bonds in a molecule to produce new compounds. It is the reverse of an esterification (condensation) reaction.
-
Ester + water
- Cannot occur at SLC
- Requires heat and a dilute acid as a catalyst
- Produces a carboxylic acid and an alcohol
TIP: Hydro means water and lysis is to break apart.
Oxidation of primary alcohols
The primary alcohol is first oxidised to an aldehyde which is then further oxidised to a carboxylic acid.
-
Primary alcohol → aldehyde
- Requires MnO₄⁻ (oxidant) and H+
- Limit the heat of the reaction
- Limit the oxidant available in the reaction
- Remove the aldehyde as it’s being produced by distillation
-
Aldehyde → carboxylic acid
- Requires MnO₄⁻ and H+
- Higher temperatures
Transesterification reactions
Process of exchanging an ester’s organic functional group with the organic group of an alcohol.
-
Triglycerides + alcohol (methanol)
- Requires a catalyst (KOH)
- Produces biodiesel and glycerol
Condensation reactions (formation) of biomolecules
-
Proteins (polypeptides)
- Peptide link joins amino acids
- Water is released
-
Carbohydrates
- Glycosydic link (−COC−) joins monosaccharides
- Water is released
-
Lipids (fats and oils)
- 3 long chain fatty acids react with glycerol
- Water is released
Hydrolytic reactions (break down) of biomolecules
-
Proteins
- Requires water and enzymes
- Peptide bond breaks, causing the protein to be broken down into individual amino acids
-
Carbohydrates
- Requires water and enzymes
- Carbs are broken down into monosaccharides
- This produces glucose (main energy source)
-
Lipids (fats and oils)
- Requires water and enzymes
- Triglycerides broken down into fatty acids and glycerol
