Organic Chemistry: Nitrogen Compounds (Edexcel International A Level (IAL) Chemistry): Flashcards

In the reduction of a nitrile, the -CN group is reduced to an -NH₂ group, forming a primary amine.

The basicity of an amine is its ability to donate the lone pair of electrons on nitrogen to a proton (H⁺), forming a dative covalent bond.

Alkyl groups have a positive inductive effect, donating electron density to the nitrogen atom and making the lone pair more available to accept a proton.

False.

In aromatic amines such as phenylamine, the lone pair on nitrogen is delocalised into the benzene ring, making it far less available to accept a proton.

An ionic ammonium salt is formed. For example, methylamine and HCl form methylammonium chloride, CH₃NH₃⁺Cl^-.

When a primary amine reacts with an acyl chloride, the product is an amide and HCl is eliminated.

A quaternary ammonium salt has all four hydrogen atoms on the nitrogen replaced by alkyl groups. It forms when a primary amine reacts with excess halogenoalkane through repeated nucleophilic substitution.

True.

Sodium hydroxide is a strong base that deprotonates the ammonium salt, releasing the free amine.

Phenylamine is an aromatic amine with the formula C₆H₅NH₂, consisting of a benzene ring directly attached to an -NH₂ group. It is also called aniline or aminobenzene.

Nitrobenzene is reduced using tin (Sn) and concentrated hydrochloric acid, heated under reflux. The tin and HCl act together as the reducing agent.

In the reduction of nitrobenzene under acidic conditions, the initial product is the phenylammonium ion rather than phenylamine itself.

Excess sodium hydroxide solution is added to deprotonate the phenylammonium ion, forming phenylamine.

The lone pair on the nitrogen atom in phenylamine is delocalised into the benzene ring, making it less available to donate to a proton and reducing its basicity.

Diazotisation is the reaction of phenylamine with nitrous acid (formed from NaNO₂ and HCl) below 10 °C to form a diazonium ion, C₆H₅N₂⁺.

Above 10 °C the diazonium ion thermally decomposes to benzene and nitrogen gas, so ice must be used to keep the temperature low.

An azo compound is an organic compound containing an R₁-N=N-R₂ group. Azo compounds are highly coloured and widely used as dyes.

In a coupling reaction, the diazonium ion acts as an electrophile and substitutes into the benzene ring of phenol at the 4th position.

False.

The -N=N- group acts as a bridge extending delocalisation through both benzene rings, making azo compounds very stable.

An amide is an organic compound containing the -CONR₂ functional group, where a carbonyl group is directly bonded to a nitrogen atom.

A condensation reaction. Two molecules join together and a small molecule (HCl) is eliminated to give the amide product.

Reacting propanoyl chloride with excess ammonia gives propanamide and ammonium chloride as products.

The HCl eliminated in the reaction is acidic and reacts with ammonia to form ammonium chloride. Excess ammonia ensures the HCl is neutralised rather than reacting back with the amide product.

True.

A primary amine has one alkyl group on nitrogen. After the condensation reaction, the nitrogen in the product retains that alkyl substituent, making it a substituted amide.

The electronegative chlorine withdraws electron density from the carbonyl carbon, making it electron-deficient and readily attacked by nucleophiles such as the lone pair on nitrogen.

A non-substituted amide is an amide in which both hydrogen atoms remain on the nitrogen (-CONH₂), formed when an acyl chloride reacts with ammonia rather than a primary or secondary amine.

In amide formation, the nitrogen lone pair acts as a nucleophile and attacks the electron-deficient carbonyl carbon of the acyl chloride.

Condensation polymerisation is a process in which monomers join together repeatedly, eliminating a small molecule (such as water or HCl) at each step to form a polymer.

Addition polymers contain no functional groups linking monomers (the backbone is all C-C bonds), whereas condensation polymers have ester or amide bonds linking the repeat units.

A polyester is formed by condensation polymerisation between a dicarboxylic acid and a diol, with water eliminated at each step.

A diamine (containing two -NH₂ groups) and either a dicarboxylic acid (containing two -COOH groups) or a dioyl dichloride (containing two -COCl groups).

True.

In addition polymerisation the C=C double bond opens to link monomers together, with no atoms lost in the process.

A repeat unit is the smallest group of atoms that, when connected repeatedly, makes up the polymer chain. It is represented in square brackets in structural formulae.

The repeat unit is identical to the monomer except the C=C double bond becomes a C-C single bond when the polymer chain forms.

A hydroxycarboxylic acid can polymerise alone because it contains both an -OH group and a -COOH group in the same molecule.

True.

Amino acids link through peptide bonds (amide links) via condensation reactions, eliminating water at each step to form polypeptide chains.

Nylon-6,6 is a synthetic polyamide made by condensation polymerisation of 1,6-diaminohexane and hexane-1,6-dioic acid. The '6,6' refers to the six carbon atoms in each monomer.

1. 1,6-diaminohexane (hexane-1,6-diamine)

2. Hexane-1,6-dioic acid (or its dioyl dichloride equivalent)

Kevlar is made from 1,4-diaminobenzene and benzene-1,4-dicarboxylic acid by condensation polymerisation.

The polymer chains are neatly aligned and held together by many hydrogen bonds, producing a tough, strong and fire-resistant material.

Poly(ethenol) is an addition polymer (also called poly(vinyl alcohol)) that is not made directly from its monomer, but by hydrolysis of poly(ethenyl ethanoate) via ester exchange with methanol.

Poly(ethenol) contains many -OH groups that form hydrogen bonds with water molecules, giving it water solubility. The degree of solubility depends on how many ester groups have been replaced.

False.

Poly(ethenol) is made in two stages: first polymerising ethenyl ethanoate, then converting the ester groups to -OH groups by ester exchange with methanol.

1. Disposable laundry bags in hospitals, which dissolve in the wash

2. Liquid-detergent capsules for washing machines and dishwashers

Polyamide chains are held together by many hydrogen bonds, giving them high strength and toughness.

A zwitterion is an ion that carries both a positive charge (-NH₃⁺) and a negative charge (-COO^-) within the same molecule, formed by internal proton transfer in an amino acid.

Amino acids exist as zwitterions, giving them strong ionic intermolecular forces of attraction that hold the crystal lattice together and make them soluble crystalline solids.

The isoelectric point is the pH at which an amino acid exists entirely as a neutral zwitterion, with equal numbers of positive and negative charges.

When acid is added to an amino acid solution, the -COO^- group accepts a proton to become -COOH and the zwitterion becomes positively charged.

The -NH₃⁺ group donates a proton to the hydroxide ion, regenerating the -NH₂ group and making the zwitterion negatively charged.

A peptide bond is an amide bond formed between the -COOH group of one amino acid and the -NH₂ group of another by a condensation reaction, eliminating water.

True.

Amino acids are amphoteric: the -NH₂ group is basic and the -COOH group is acidic, so amino acids react with both acids and alkalis.

The alpha-carbon bearing the R group, -NH₂, -COOH and -H groups is a chiral centre with four different substituents, so the molecule is not superimposable on its mirror image.

A polypeptide is formed when many amino acids join together through peptide bonds in a condensation polymerisation.

True.

Amino acid solutions resist pH changes because the zwitterion can accept a proton (via -COO^-) or donate one (via -NH₃⁺) when small amounts of acid or alkali are added.