Stage 2 Organic Chemistry

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homologous series:
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family of organic compounds
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saturated
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single bonds
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unsaturated
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double or triple bonds
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aromatic
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benzene ring
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meth
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1
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eth
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2
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pop
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3
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but
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4
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pent
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5
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hex
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6
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hept
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7
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oct
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8
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non
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9
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dec
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10
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Methyl
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– CH₃
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Ethyl
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– CH₂CH₃
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alkanes
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no functional group
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Secondary interactions
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occur between 8+ and a 8- ends between molecules
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hydrogen bonding
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a secondary interaction between a 8+ hydrogen on one molecule and a 8- N,O or F on another molecule. it is the strongest type of bonding.
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dipole-dipole attraction
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secondary interactions between a 8+ atom on one molecule and a 8- atom on another molecule. not as strong as hydrogen bonding.
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dispersion forces
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weakest type of attraction which exists between all molecules. these are only discussed when there are no other types of secondary interaction present. Usually when there are no significant 8+ and 8- ends.
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melting and boiling points of organic compounds
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melting and boiling points of organic compounds with the same functional group increase with the length of carbon chain.
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type of bonding between aldehydes
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dipole-dipole
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type of bonding between alcohols
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hydrogen bonding
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type of bonding between ketones
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dipole-dipole
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type of bonding between esters
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dipole-dipole
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type of bonding between carboxylic acids
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hydrogen bonding
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What are organic compounds’ solubility in water?
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Organic compounds are generally insoluble in water
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what helps solubility in water?
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hydrogen bonding between functional groups and water can explain the solubility in water of some smaller organic compounds.
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why are non-polar organic compounds (such as hexane) not soluble in water?
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Non-polar compounds will not dissolve in polar water. Non-polar compounds will only dissolve in other non-polar compounds. Water molecules are much more attracted to each other than the hexane due to the strong hydrogen bonding between.
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Non-polar molecules
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Molecules with polar functional groups but long chains (6 C atoms or more) are classified as non-polar as the non-polar chain is the dominant structural feature of the molecule.
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What does the solubility of an organic compound in water depend on?
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The solubility of an organic compound depends on its molar mass and the functional groups present.
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When a non-polar chain length increases…
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molecules take on greater non-polar character overall
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When a molecule’s non-polar chain is longer this means…
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the molecule decreases in solubility
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A large molecule that has a number of polar functional groups can be…
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soluble in water
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Ethanol production
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produced from fermentation of glucose, directly obtained from fruits such as grapes or from hydrolysis of larger disaccharides or polysaccharides fround in vegetables and grains
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conditions required for the production of ethanol form fermentation
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1. optimum temperature and acidity 2. anaerobic conditions required
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optimum temperature and acidity
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outside these optimum perameters, enzymes that catalyse the reaction are totally or partially ineffective.
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anaerobic conditions required
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oxygen must be excluded from the reaction vessel
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Hydrolysis and fermentation:
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(C₆H₁₀O₅)n + nH₂O → 2C₆H₁₂O₆ C₁₂H₂₂O₁₁ + H₂O → 2C₆H₁₂O₆ C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂
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1. Hydrolysis of polysaccharides to monosaccharides
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(C₆H₁₀O₅)n + nH₂O → 2C₆H₁₂O₆
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2. Hydrolysis of disaccharides to monosaccharides
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C₁₂H₂₂O₁₁ + H₂O → 2C₆H₁₂O₆
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3. Fermentation of glucose to ethanol and carbon dioxide
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yeast C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂
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hydrolysis
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chemical reaction where the splitting (‘Iysis’) of a molecule is accompanied by the addition of the pieces of the water molecule, -H and -OH
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fermentation
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action of enzymes on carbohydrates to produce different compounds, without using oxygen
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yeasts
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produce enzymes to speed up fermentation
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primary, secondary & tertiary alcohols
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alcohols are classified as primary, secondary or tertiary depending on the position of the hydroxyl group in the molecular structure
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primary alcohols
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R – CH₂OH
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secondary alcohols
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R’ | R – C – OH | H
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tertiary alcohols
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R’ | R – C – OH | R”
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oxidation of alcohols
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the type of product, if any, formed by oxidising an alcohol depends on whether the alcohol is primary, secondary or tertiary
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oxidising primary alcohols
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H⁺/Cr₂O₇²⁻ H⁺/Cr₂O₇²⁻ primary alcohol → aldehyde → carboxylic acid heat heat
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oxidising secondary alcohols
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H⁺/Cr₂O₇²⁻ secondary alcohol → ketone heat
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oxidising tertiary alcohols
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H⁺/Cr₂O₇²⁻ tertiary alcohol → no reaction. heat
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what is the oxidising agent?
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acidified dichromate
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what do oxidising agents cause?
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oxidising agents cause oxidation, therefore it is itself reduced
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Half equation of oxidation:
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6e⁻ + Cr₂O₇²⁻ + 14H⁺ → 2Cr³⁺ + 7H₂O orange green
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As a non-polar C chain of the alcohol increases, the molecule overall becomes more…
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non-polar
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When the non-polar C chain of the alcohol increases, the overall effect of the H-bonding…
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decreases
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When the non-polar C chain of the alcohol increases its solubility in water will…
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decrease
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When the non-polar C chain of the alcohol increase, its solubility in non-polar solvents will…
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increase
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When the non-polar C chain of the alcohol increases, its solubility in polar solvent such as water will be…
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lower
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When there are more polar hydroxyl functional groups present on a molecule, its solubility in a polar solvent such as water will be…
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higher
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Differences between aldehydes and ketones
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Both contain the carbonyl gropu, C = O. The main difference is that the carbonyl group is in a terminal position in aldehydes, whereas in ketones it is in a non-terminal position.
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Aldehydes and ketones have a…
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polar C = O bond
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what type of secondary interactions occur between aldehyde and ketone molecules?
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dipole-dipole interactions occur between these molecules.
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aldehydes and ketones have higher boiling points than…
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alkanes of similar molar mass
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aldehydes and ketones have lower boiling points have lower boiling points than…
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alcohols
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what type of bonding doesn’t occur between aldehydes and ketones?
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there are no hydrogen’s involved in polar bonds therefore there are no hydrogen bonds between molecules. Aldehydes and ketones do not H bond to each other.
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Solubility of aldehydes and ketones
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both aldehydes and ketones are able to form H-bonds with water. lower members of both homologous series are very soluble in water. Solubility decreases with higher members of series as non-polar HC outweighs polar carbonyl groups.
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Oxidation of aldehydes
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Aldehydes are prepared by oxidation of the corresponding primary alcohol
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Oxidation of ketones
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Ketones are prepared by oxidation of corresponding secondary alcohol
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What are the commonly used oxidising agents?
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acidified potassium dichromate (H⁺/Cr₂O₇²⁻) acidified potassium permangate (H⁺/MnO₄⁻)
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Distinguishing between aldehydes and ketones with acidified dichromate (in acidic conditions)
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H⁺/Cr₂O₇²⁻ Aldehyde: aldehyde → carboxylic acid heat Cr₂O₇²⁻ reduced: Cr₂O₇²⁻ + 14H⁺ + 6e⁻ → 2Cr³⁺ + 7H₂O H⁺/Cr₂O₇²⁻ Ketone: ketone → no reaction heat
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distinguishing between aldehydes and ketones with ammoniacal silver nitrate (in basic conditions)
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ammoniacal silver nitrate aldehyde → carboxylate ion (forms silver mirror) ketones do not form silver mirror
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What happens when aldehydes are oxidised with ammoniacal silver nitrate?
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Aldehydes react with ammoniacal silver nitrate and are oxidised to carboxylate ions. The oxidising agent is reduced to metallic silver, therefore creating a silver mirror effect.
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What happens when ketones are oxidised with ammoniacal silver nitrate?
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Ketones do not form a silver mirror when ammoniacal silver nitrate is added.
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Polarity of carboxylic acids
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Carboxylic acid functional groups are more polar than alcohol functional groups. There are more opportunities for hydrogen bonding to occur between carboxylic acid groups .Carboxylic acids have a higher boiling point.
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Polarity of acids and esters
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Esters are less polar than carboxylic acids. They can only form dipole-dipole interactions between molecules. Acids form extensive H bonding between molecules which are stronger and therefore require more energy to break.

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