Edexcel A Level Chemistry: 18: Organic Chemistry III
This flashcard set introduces aromatic and aliphatic compounds, highlighting the presence or absence of delocalised electrons in hydrocarbon rings. It also describes benzene as an arene and outlines its key physical properties.
What are aromatic compounds?
Compounds containing a hydrocarbon ring containing delocalised electrons
Key Terms
What are aromatic compounds?
Compounds containing a hydrocarbon ring containing delocalised electrons
What are aliphatic compounds?
Ones which do not have a hydrocarbon ring with delocatised electrons
What is benzene described as?
An arene
What are the physical properties of benzene?
A colourless liquid
Boiling temperature of 80 degrees
Insoluble in water
What is the molecular formula of benzene?
C6H6
What is the Kekule structure of benzene?
Alternating double and single bonds in a cyclic structure with a ring of hydrogen around it
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| Term | Definition |
|---|---|
What are aromatic compounds? | Compounds containing a hydrocarbon ring containing delocalised electrons |
What are aliphatic compounds? | Ones which do not have a hydrocarbon ring with delocatised electrons |
What is benzene described as? | An arene |
What are the physical properties of benzene? | A colourless liquid |
What is the molecular formula of benzene? | C6H6 |
What is the Kekule structure of benzene? | Alternating double and single bonds in a cyclic structure with a ring of hydrogen around it |
How does bromine water disprove the Kekule structure? | If benzene contained three C=C bonds, it would readily decolourise bromine water, but it does not, suggesting there are no double bonds |
How do the isomers of dibromobenzene disprove the Kekule structure? | If the Kekule structure is correct, there would be four isomers of dibromobenzene, however only three are known to exist as there are no C=C bonds |
How do bond lengths disprove the Kekule structure? | C-C bonds and C=C bonds are different lengths, but in benzene the bonds lengths are all the same, so there cannot be different types of bonds in the molecule |
How do enthalpy changes of hydrogenation disprove the Kekule structure? | The actual enthalpy change of hydrogenation of benzene differs from the theoretical value for if it had C=C double bonds |
What are the four factors which disprove the Kekule structure? | Bromine water |
In the actual structure of benzene how are the electrons aranged? | In two delocalised rings, one above and one above the Carbon ring, of pi electrons |
What are the conditions needed for hydrogenation of benzene? | Hydrogen, and heating under pressure with a nickel catalyst |
What is the equation for the hydrogenation of benzene? | C6H6 + 3H2 ——> C6H12 |
What type of flame does benzene give? | A smoky flame |
What are halogen carriers? | Usually metal-halogen compounds such as aluminium chloride |
What are the products of bromination of benzene? | Bromobenzene and hydrogen bromide |
What is nitration of benzene? | The substitution of a hydrogen atom by a nitro group, NO2 |
What are the conditions needed for nitration of benzene? | Warming it with a mixture of conc nitric acid and sulfuric acid catalyst |
What are the products of nitration of benzene? | Nitrobenzene and water |
What are two of the types of Friedel-Crafts reactions? | Alkylation and acylation |
What are the features all Friedel-Crafts reactions have in common? | Using reagent XY, one of the hydrogens In benzene is substituted by Y, and the other product is HX |
What is an alkyl group? | CH3 |
What is an acyl group? | COCH3 |
What is the reactant for alkylation of benzene? | A halogenalkane, such as CH3Cl |
What are the products of alkylation of benzene? | An alkylbenzene such as methylbenzene and hydrogen chloride |
What are the products of the acylation of benzene? | A ketone (phenylethanone) and hydrogen chloride |
What name is often used when the benzene ring is attached of another functional group? | Phenyl or phen |
What makes benzene act as an electrophile? | The delocalised electrons |
How does Bromine react with the catalyst in Bromination of Benzene? | It forms Br+ |
What is the equation for the reaction between Bromine and the halogen carrier in Bromination? | AlCl3 + Br2 ——> Br+ + AlCl3Br- |
What are the inorganic products formed in the bromination of benzene? | AlCl3 and HBr |
What is the first step in Nitration of Benzene? | Formation of an electrophile through nitric acid and sulfuric acid reacting to form NO2+ |
What is the equation for the reaction to form an electrophile? | HNO3 + H2SO4 ——> NO2+ HSO4- +H2O |
What type of mechanism is Alkylation of benzene? | Electrophillic substitution |
What are the inorganic products in alkylation? | HCl and AlCl3 |
What are the organic products in acylation? | HCl and AlCl3 |
What does Friedel-Crafts Acylation produce? | Phenylketones |
What is benzene refluxed with in acylation? | An acyl chloride |
What must the temperature be kept below for nitration of benzene? | 55 degrees C |
What happens if the temperature is above 55 for nitration of benzene? | Multiple substitutions occur |
Why is phenol more reactive than benzene | The OH group makes it more likely to undergo electrophillic substitution |
What happens if you shake phenol with bromine water? | It decolourises it |
Why does substitution occur more than once on phenol? | The OH group makes it very attractive to electrophiles |
What can aspirin be synthesised from? | Salicylic acid and ethanoic anhydride |
What is the amine functional group? | -NR2, where R is an alkyl group or hydrogen |
What can aliphatic amines be made from? | Halogenoalkanes or nitriles |
What are amines? | Weak bases, as they accept protons |
What does the strength of the amine base depend on? | How available the nitrogen's lone pair of electrons is |
What is the order of basicity? | Primary aromatic amine < Ammonia < Primary aliphatic amine |
Why are the aliphatic amines the strongest bases? | The distribution of negative charge is distributed entirely on the lone pair, whereas in the aromatic amine it is distributed widely |
What are small amines soluble in? | Water, as the amine group can form hydrogen bonds with the water molecule |
The bigger the amine the greater the… | …London forces |
What kind of solutions do amines form? | Alkaline |
What do amines form with Copper (II) ions? | Complex ions |
What complexes do Cu2+ ions form with water? | [Cu(H2O)6]2+ - a blue solution |
What complex is formed if a small amount of butylamine solution is added? | [Cu(OH)2(H2O)4] - a blue precipitate |
If more butylamine solution is added, how does the complex change? | [Cu(CH3(CH2)3NH2)4(H2O)2]2+ - a deep blue solution |
How do amines react with halogenoalkanes? | In nucleophillic substitution reactions |
How can N-Substituted Amides be made from amines? | By acetylation |
Amides are… | …carboxylic acid derivatives |
What is the amide functional group? | -CONH2 |
Why do amides behave differently from amines? | Because the carbonyl group pulls electrons away from the rest of the group |
What suffix do amides have? | -amide |
What can amides be made from? | Acyl chlorides |
What are the reactants needed to make a primary amide? | An acyl chloride and concentrated ammonia |
What reactants are needed to make an N-substituted amide? | An acyl chloride and primary amine |
What is an N-substituted amide? | One of the hydrogens in NH2 is substituted with an alkyl group |
What are amide links? | -CONH- |
What reacts to form an amide link? | -COOH and -NH2 |
Which two types of molecule form a polyamide? | Dicarboxylic acids and diamines |
What are proteins? | Condensation polymers of amino acids |
What is needed to hydrolyse a protein into amino acids? | 6moldm-3 hydrochloric acid and reflux |
Which two types of molecule form a polyester? | Dicarboxylic acids and diols |
What is an ester link? | -COO- |
What functional groups do amino acids have? | NH2 and COOH |
What is a zwitterion? | An overall neutral molecule that has a positivie and negative charge on different parts of the molecule |
In acidic conditions, which part of the amino acid is changed? | The NH2 becomes protonated, forming NH3+ |
What charges does the amino acid have at its isoelectric point? | The NH2 becomes NH3+ and the COOH becomes COO- |
In alkaline conditions, which part of the amino acid is changed? | The COOH group becomes COO- |
Most amino acids are… | …chiral |
What can be used to identify unknown amino acids? | Paper chromatography |
How would you calculate an Rf value? | Distance travelled by spot/distance travelled by solvent |
What is the general formula of a Gringard reagent? | RMgX |
How are Gringards reagents made? | By refluxing a halogenoalkane with magnesium in dry ether |
What would a Gringard's reagent + CO2 form? | A carboxylic acid |
What are the conditions needed to form a carboxylic acid from Gringards and CO2? | Dry ether and dilute HCl |
What do Gringards form in reaction with aldehydes and ketones? | Alcohols |
What are the conditions needed to form an alcohol from Gringards + carbonyl? | Dry ether and dilute HCl |