Acid Anhydrides

• Acid anhydrides are made from two carboxylic acids joined together in a condensation reaction.
  
  
  
  
  
  
   

• Acid anhydrides react in similar ways to acyl chloride but are less reactive, making them generally safer to use. 

• Acid Anhydride + Alcohol → Ester + Carboxylic Acid
   

Acyl Chlorides

• Acyl chlorides are highly reactive and easily react with nucleophiles, they have the functional group:
  
  
  
  
  
  
   

• They are prepared by reacting a carboxylic acid with phosphorus pentachloride (PCl  ) in anhydrous conditions (acyl chlorides react easily with water). 

• Acyl chlorides react with nucleophiles bonded to a hydrogen atom in addition-elimination reactions:
  
  
  
  
  
  
  
  Key reactions 
   

• Acyl Chloride + Water → Carboxylic Acid (+ HCl)

• Acyl Chloride + Alcohol → Ester (+ HCl)

• Acyl Chloride + Ammonia → Primary Amide (+ Ammonium Chloride)

• Acyl Chloride + Primary Amine → Secondary Amide (+ Alkyl Ammonium Chloride)

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Carboxylic Acids

• A carboxylic acid group can lose a proton to become a negatively charged carboxylate ion.
  
  
  
  
  
  
  
  
   

• Carboxylic acids can be formed by the oxidation of a primary alcohol with acidified potassium dichromate, under reflux conditions.

• Carboxylic acids can be reduced to primary alcohols using hydride ions (from lithium tetrahydridoaluminate (LiAlH )).

• The reduction must be in dry ether as LiAlH  reacts violently with water molecules.

• Negatively charged carboxylate ions can bond ionically with positive ions, forming carboxylate salts.
   

Carbonyls (reduction of)

• A carbonyl group is a carbon double bonded to an oxygen atom (C=O).

• Aldehydes have a carbonyl group at the end of a carbon chain; ketones have a carbonyl group in the middle of a carbon chain. 

• Aldehydes can be formed from the oxidation of primary alcohols; ketones can be formed from the oxidation of secondary alcohols.

• The slightly positive carbon in an aldehyde and a ketone reacts with nucleophiles in addition reactions.

• Aldehydes can be reduced with hydride ions (H⁻) to primary alcohols; ketones can be reduced with hydride ions to secondary alcohols.

• A common source of hydride ions for reduction is the compound lithium tetrahydridoaluminate (LiAlH  )

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Identifying Carbonyls

• Aldehydes can be oxidised to carboxylic acids. It is not possible to oxidise a ketone.

• The ability to further oxidise an alcohol and not a ketone can be used to help distinguish between aldehydes and ketones.

• Aldehydes can be identified by using Tollens’ reagent (silver precipitate formed) or Fehling’s solution (red precipitate formed).  

• Aldehydes and ketones can both be identified by using Brady’s reagent, producing an orange precipitate.

• A methyl carbonyl group can be identified using a (warm) mixture containing iodine and sodium hydroxide, forming a yellow solid.

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Nucleopilic Addition of Carbonyls

• Hydrogen cyanide reacts with carbonyl groups in nucleophilic addition reactions forming hydroxynitriles:
  
  
  
  
  
  
  
   

• Hydrogen cycande is highly reactive (and toxic), it can be prepared ‘in situ’ using a metal cyanide (KCN or NaCN) and sulfuric acid (H SO ). 

• The length of the carbon chain in a carbonyl molecule can be extended using this reaction

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Esters

• Esters are made from a carboxylic acid and alcohol held together by an ester link.

• An ester is formed in an esterification reaction by reacting a carboxylic acid and alcohol together, in the presence of concentration sulfuric acid (under reflux conditions).

• Esterification is a condensation reaction as water is released as a product.

• Ester links can be broken in hydrolysis reactions (addition of water).

• Hydrolysis of an ester in acidic conditions produces a carboxylic acid and alcohol.

• Hydrolysis of an ester in alkaline conditions produces a carboxylate ion and alcohol.

• Fats and oils are natural examples of esters, called tri-glycerides, made from glycerol (propane-1,2,3-triol) and long chain fatty acids (carboxylic acids with long carbon chains).​

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Naming of Esters

• Esters are named based on the length of the carbon chains in both the carboxylic acid and alcohol that are used to make the ester.

• The general form is alkyl-carboxylate.
  
  
  
  
   

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• The first part of the name comes from the carbon chain in the alcohol (-alkyl).

• The second part of the name is the same as the carboxylate ion of the carboxylic acid (-carboxylate).

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Optical Isomerism

• Carbon can form four covalent bonds, if a carbon atom is bonded to four different groups there are two possible ways of arranging the groups, creating two possible isomers
  
  
  
  
  
  
  
   

• Each isomer is a mirror image of the other and both isomers rotate plan polarised light in opposite directions.

• If equal amounts of both isomers are present in a mixture, there is no overal rotation of plane polarised light - the mixture is racemic.

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Benzene Structure

• Benzene is a cyclic hydrocarbon made of six carbon atoms and six hydrogen atoms (C H ).

• The Kekule structure shows bonding in benzene as alternating carbon double bonds.

  • Bond length data and enthalpies of hydrogenation for benzene show this to be incorrect

• Each carbon atom has an un-bonded electron in a p-orbital. The p-orbitals of all carbon atoms merge to create two rings of electron density - spreading electrons throughout the carbon ring (delocalised electrons)
  
  
  
  
  
  
  
   

• Due to the delocalised electron rings, benzene molecules are easily attacked by electrophiles.

• Compounds that contain benzene are called aromatic compounds.

  • The study of these compounds is called aromatic chemistry.
    
     

Benzene Reactions

• Electrophiles (electron deficient species) are attracted to the ring of delocalised electrons in benzene, nucleophiles are repelled by the delocalised electrons.

  • Benzene reacts with strong electrophiles​

• Electrophiles react with benzene in electrophilic substitution reactions, forming a bond with a carbon atom in the ring and forcing the hydrogen atom already bonded to the carbon atom to be lost.
  
  
  
  
  
  
  
   

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Nitration of Arenes

• The nitration of an arene (compound with a benzene ring in) is an electrophilic substitution reaction, with a nitronium ion, NO⁺ , acting as the electrophile.​

• The nitronium ion is produced by reacting concentrated nitric acid with concentrated sulfuric acid:
  
  
  
   

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• The reaction is carried out at 55ºC and produces a nitroarene.
  
   

Acylation of Arenes

• Acylation of benzene involves the substitution of an acyl group onto a benzene ring:
  
  
  
  
  
  
  
  
  
   

• Acyl chlorides are reacted with a halogen carrier (AlCl ) to form an acyl ion, which acts as a strong electrophile and reacts with the benzene ring in an electrophilic substitution reaction. 

• The reaction requires warm conditions, and HCl is formed as a product.
  
   

Alkylation of Arenes

• Alkylation of benzene involves the substitution of an alkyl group onto a benzene ring.

• Alkyl groups are carbon chains bonded to another carbon atom (i.e. methyl).
  
  
  
  
  
  
  
  
  
  
  
   

• Halogenoalkanes are reacted with a halogen carried to produce an R group with a positive charge that can act as the required electrophile.

• The reaction requires warm conditions, and HCl is formed as a product.

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Bromination of Arenes

• The bromination of benzene involves the electrophilic substitution of a bromine onto a benzene ring:
  
  
  
  
  
  
  
  
   

• A halogen carrier is needed (usually AlBr ) to create an electrophile, as the delocalised electrons in the benzene are unable to polarize the bromine molecule sufficiently (unlike with bromine and alkenes).

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Phenol

• Phenol is an organic molecule that has a benzene ring with a hydroxyl group attached:
  
  
  
  
  
  
   

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• The lone pair on the oxygen atom merges with the pi-bonding system in benzene, enabling the OH⁻ group to release a proton.

  • This means phenol can act as a weak acid.​

• Alcohols are not weak acids as a negative charge on the oxygen atom is not stabilised.

Phenol Reactions

• The hydroxyl group (OH) in phenol ‘activates’ the benzene ring, making it more reactive with electrophiles.

• Phenol is able to react directly with bromine (unlike benzene) in multiple substitution reacts to produce 2,4,6-tribromophenol.

• Nitration of phenol is easier than nitration of benzene. Only nitric acid (HNO ) at room temperature is required (for nitration of benzene: nitric acid, sulfuric acid and temperature of 55ºC).

• The OH group in phenol has a directing effect, meaning substitutions are most likely to occur on the second, fourth and sixth carbon (carbon one is occupied by the OH group.

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Amines

• Amines contain a carbon chain bonded to a nitrogen atom that is bonded to either hydrogen or another carbon chain (alkyl).

• Amines can be primary, secondary or tertiary (quaternary amines exist as positively charged ions). 

• A lone pair of electrons on the nitrogen atom enables amines to act as bases (and nucleophiles).

• Primary amines are less basic than secondary amines, and secondary amines are less basic than tertiary amines. 

• This is due to the positive inductive effect of alkyl chains.

• Aromatic amines are weak bases as the benzene ring is electron withdrawing.
   

Producing Primary Amines

• Primary amines are formed by the reaction of a halogenoalkane with ammonia.
  
  
  
  
  
  
  
   

• Ammonia acts as a nucleophile and is substituted for the halogen, making the mechanism nucleophilic substitution.

• Ammonium ions are formed at the end of the reaction because the ammonia (not the halide ions) removes a proton from the positively charged nitrogen in the intermediate.

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Producing Secondary and Tertiary Amines

• If a halogenoalkane is reacted with an excess of ammonia, a primary amine is formed.

• When insufficient ammonia is present to undergo substitution with all the halogenoalkane molecules, the primary amines that did form undergo further substitution and can become secondary, tertiary and quaternary amines.

• Once four substitutions have happened, the nitrogen has four bonds and becomes positively charged. This quaternary ammonium ion is attracted to negative halide ions and a quaternary ammonium salt forms

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Producing Aromatic Amines

• Aromatic amines are formed by the reduction of a nitroamine:
  
  
  
  
  
  
  
  
  
  
   

• A tin catalyst and concentrated hydrochloric acid are used under reflux conditions (reflux conditions are essential to stop gaseous vapors of hydrochloric acid being released). 

• Acidic conditions result in an ammonium ion being formed, which is converted into an amine group by adding sodium hydroxide.

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Amides

• Amides are carboxylic acid derivatives that have a carbonyl group with an amine attached to the carbon from the carbonyl, they are generally unreactive.
  
  
  
  
  
  
   

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• Amides can be primary, secondary and tertiary. 

• (Primary) amides are formed from acyl chlorides and ammonia in a nucleophilic addition-elimination reaction, producing an ammonium chloride salt.

• Secondary amides are formed from acyl chlorides and a primary amine. 

• Tertiary amides are formed from acyl chlorides and a secondary amine.

Organic Dyes

• Organic dyes are compounds bonded to materials to give the material a specific colour.

• Within organic dyes, electrons are excited from low energy to high energy by absorbing energy from the visible part of the electromagnetic spectrum.

• The part of the dye where the excitation of electrons occurs is called the chromophore.

• Most organic molecules absorb higher energy waves (ultraviolet light – not visible) to excite electrons. Increased levels of electron delocalisation decrease the energy required to excite electrons and enable visible light to be absorbed by the molecule, forming a chromophore. 

• Wavelengths of light not absorbed by the chromophore are scattered by the dye and are observed as the complimentary colour to the colour of light absorbed by the dye.
   

Azo-Dye Formation

• The chromophore in an organic dye requires a high level of electron delocalization.

• Azo dyes are compounds formed from a diazonium salt and an aromatic compound (usually phenol)
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
   

• The formation of azo dyes happens in two stages:

• A diazonium salt is formed from the reaction of phenylamine with nitrous acid and hydrochloric acid. 

• The diazonium salt is coupled with the phenol by reacting them together with sodium hydroxide.

• Diazonium salts are highly unstable and to stop them decomposing during the reaction, low temperatures are used (5ºC).

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Addition Polymerisation

• Polymers are long chain molecules made of repeating units bonded together.

• Molecules that form repeating units are called monomers. 

• Alkenes can undergo addition polymerisation to create polyalkenes.

  • The double carbon bond can be opened to enable each carbon from the double bond to form new bonds with another repeating unit. 
     

Condensation Polymerisation

• Condensation polymers are formed when monomers bond together and one water molecule is released per bond.

• To break apart a condensation polymer (into its monomers), a water molecule is needed and a hydrolysis (breaking of bond with water) reaction happens.

• Polyamides are formed from the reaction of a di-carboxylic acid with a di-amine. The links between each monomer are called a peptide links.

• Polyesters are formed from the reaction of a di-carboxylic acid with a di-ol in the presence of an acid. 

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Amino Acids and Proteins

• Amino acids are a collection of different organic molecules that all contain an amine group and a carboxylic acid group.
  
  
  
  
  
  
  
  
   

• Amino acids join together to form proteins.

• The amine group in an amino acid can accept a proton (basic) to become a positive ion.

• The carboxylic acid group in an amino acid can donate a proton (acidic) to become a negative ion.

• Different amino acids lose or gain protons at different pHs.

• A zwitterion is an amino acid that has lost a proton from its carboxylic acid group but gained a proton at its amine group – forming negatively and positively charged groups, but no overall charge.

• Zwitterions are formed at an amino acid’s isoelectric point.
   

Properties of Polymers

• Longer chain polymers have higher melting points than shorter chain polymers.

• The larger the contact surface between polymers, the greater the number of intermolecular forces that can form between them, resulting in a higher melting point.

• Branched chain polymers have lower melting points than straight chained polymers as there is less contact surface between them, resulting in fewer intermolecular forces.

• Addition polymers are not biodegradable.

• Condensation polymers are biodegradable and are broken down in hydrolysis reactions.