Organic Chemistry III: Nitrogen Chemistry (Edexcel A Level Chemistry): Flashcards
Exam code: 9CHO
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Define amine.
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Define amine.
An amine is an organic compound derived from ammonia in which one or more hydrogen atoms are replaced by an alkyl or aryl group.
Amines are classified as primary, secondary, or tertiary based on the number of hydrogens replaced on the nitrogen atom.
True or False?
Secondary amines have two alkyl or aryl groups bonded directly to the nitrogen atom.
True.
In secondary amines, two hydrogen atoms of ammonia have been replaced by alkyl or aryl groups. The nitrogen therefore carries two R groups and one hydrogen.
Define primary amine.
A primary amine is an amine in which one hydrogen atom of ammonia has been replaced by an alkyl or aryl group, giving the general formula RNH2.
Amines with an alkyl R group are called .......... amines, while those with an aryl R group are called .......... amines.
Amines with an alkyl R group are called aliphatic amines, while those with an aryl R group are called aromatic amines.
Define amide.
An amide is an organic compound with the general structure RCONR2, formed by the condensation reaction of a carboxylic acid or acyl chloride with ammonia or an amine.
What are the two functional groups present in naturally occurring amino acids, and what property does having both give them?
Naturally occurring amino acids contain an amino (-NH2) group and a carboxylic acid (-COOH) group.
Having both a basic and an acidic group makes amino acids amphoteric — they can act as both acids and bases.
True or False?
In amine classification, primary refers to one substituent on the carbon adjacent to nitrogen.
False.
Unlike alcohols and haloalkanes, amine classification is based on the number of substituents on the nitrogen atom, not on the adjacent carbon atom.
Define amino acid.
An amino acid is an organic compound containing both an amino (-NH2) group and a carboxylic acid (-COOH) group.
Because both groups are present, amino acids are amphoteric — they can act as both acids and bases.
How are primary amides named, and what is the name of CH3CONH2?
Primary amides are named by adding the suffix -amide to the stem name of the parent chain.
CH3CONH2 has a two-carbon chain (ethan-) and an amide group, giving the name ethanamide.
Define quaternary ammonium salt.
A quaternary ammonium salt is an ionic compound in which all four hydrogen atoms of the ammonium ion have been replaced by alkyl groups, giving a positively charged nitrogen centre.
What is observed when excess primary aliphatic amine is added to hexaaquacopper(II) ions?
First, a pale blue precipitate forms as Cu(OH)2 is produced.
With excess amine, the precipitate dissolves to give a deep blue solution as the amine acts as a ligand and displaces water molecules to form a copper-amine complex.
When a primary amine reacts with a halogenoalkane, the organic product is a .......... amine and the inorganic product is a .......... .
When a primary amine reacts with a halogenoalkane, the organic product is a secondary amine and the inorganic product is a hydrogen halide.
True or False?
A primary aliphatic amine reacts with ethanoyl chloride in an addition-elimination reaction to form an amide.
True.
The amine and acyl chloride join together and then HCl is eliminated, producing an amide product containing a carbonyl group adjacent to an NH group.
How is a primary aliphatic amine prepared from a halogenoalkane?
The halogenoalkane is reacted with excess hot ethanolic ammonia under pressure.
Ammonia acts as a nucleophile, and its lone pair replaces the halogen in a nucleophilic substitution reaction to give a primary amine.
When methylamine dissolves in water, it reacts to form .......... ions and hydroxide ions, producing an .......... solution.
When methylamine dissolves in water, it reacts to form methylammonium ions and hydroxide ions, producing an alkaline solution.
How is a primary amine prepared from a nitrile?
The nitrile is reduced using either LiAlH4 in dry ether or hydrogen gas over a nickel catalyst.
The -CN group is converted to an -NH2 group, giving a primary amine.
True or False?
Adding NaOH to a methylammonium salt regenerates the free amine.
True.
The hydroxide ions from NaOH deprotonate the ammonium salt, converting it back to the free amine (methylamine) and water.
Why does the reaction of a tertiary amine with a halogenoalkane not produce HCl, unlike the reaction with a primary or secondary amine?
In a tertiary amine, there is no N–H bond, so no hydrogen is available to be lost as HCl.
Instead, the halide ion remains as the counter-ion, forming a quaternary ammonium salt.
True or False?
Phenylamine forms a basic solution when dissolved in water.
True.
Phenylamine is a very weak base — its lone pair is partially delocalised into the benzene ring, greatly reducing its ability to accept protons. However, it does react with water to a small extent and forms a very weakly basic solution.
What is amine basicity?
Amine basicity is the ability of an amine's nitrogen lone pair to accept a proton and form a dative covalent bond.
The more readily the lone pair accepts a proton, the stronger the base.
Why are primary aliphatic amines stronger bases than ammonia?
The alkyl group attached to nitrogen has a positive inductive effect — it donates electron density towards nitrogen, making the lone pair more available to accept a proton.
This makes primary aliphatic amines stronger bases than ammonia.
True or False?
Phenylamine forms a strongly basic solution when dissolved in water.
False.
Phenylamine is a very weak base. Its lone pair is delocalised into the benzene ring, greatly reducing its ability to accept protons. This makes it far less basic than aliphatic amines or ammonia.
Define positive inductive effect (in the context of amines).
The positive inductive effect is the donation of electron density along a chain of bonds by groups such as alkyl groups.
In amines, alkyl groups push electron density towards the nitrogen atom, making its lone pair more available to accept a proton and increasing basicity.
Why is phenylamine a weaker base than ethylamine?
In phenylamine, the lone pair on nitrogen is delocalised into the benzene ring, making it less available to accept a proton.
In ethylamine, the ethyl group donates electron density to nitrogen via the positive inductive effect, making the lone pair more available — so ethylamine is a stronger base.
True or False?
Secondary aliphatic amines are stronger bases than primary aliphatic amines.
True.
Secondary amines have two alkyl groups on nitrogen. The greater positive inductive effect from two alkyl groups pushes more electron density onto nitrogen than one, making the lone pair more available and the base stronger.
The lone pair on the nitrogen of phenylamine is .......... into the benzene ring, which makes it .......... basic than ammonia.
The lone pair on the nitrogen of phenylamine is delocalised into the benzene ring, which makes it less basic than ammonia.
What is reduction (in the synthesis of phenylamine)?
Reduction is the process by which nitrobenzene (C6H5NO2) is converted to phenylamine (C6H5NH2) using tin and concentrated hydrochloric acid as reducing agents under reflux.
What reagents and conditions are used in Stage 1 of the synthesis of phenylamine from nitrobenzene?
Tin (Sn) and concentrated hydrochloric acid (HCl) are used as reducing agents.
The mixture is heated under reflux in a boiling water bath. Under these acidic conditions, phenylammonium ions (C6H5NH3+) are formed.
What is done in Stage 2 of the synthesis of phenylamine, and why?
Excess sodium hydroxide solution is added to deprotonate the phenylammonium ions (C6H5NH3+).
This converts them to free phenylamine (C6H5NH2), because the acidic conditions in Stage 1 protonate the amine product.
Nitrobenzene (C6H5NO2) is reduced to phenylamine (C6H5NH2) using .......... and concentrated HCl, heated under .......... .
Nitrobenzene (C6H5NO2) is reduced to phenylamine (C6H5NH2) using tin (Sn) and concentrated HCl, heated under reflux.
True or False?
In the reduction of nitrobenzene, phenylammonium ions form before phenylamine is produced.
True.
The acidic conditions in Stage 1 protonate the amine product to give phenylammonium ions (C6H5NH3+). Excess NaOH is then added in Stage 2 to deprotonate these and release free phenylamine.
Define phenylamine.
Phenylamine is an aromatic amine with the formula C6H5NH2, consisting of a benzene ring with an attached amino (-NH2) group.
It is also known as aniline or aminobenzene.
True or False?
Phenylamine can also be called aniline or aminobenzene.
True.
All three names refer to C6H5NH2: phenylamine (systematic IUPAC-style), aminobenzene (descriptive), and aniline (common/trivial name).
Why is NaOH added after the tin/HCl reduction step in phenylamine synthesis?
The tin/HCl reduction is carried out under acidic conditions, which protonate the amine product to form phenylammonium ions.
Adding excess NaOH deprotonates these ions, releasing the free phenylamine product.
Define amide bond.
An amide bond is the –CO–NH– functional group formed when an acyl chloride reacts with ammonia or an amine in a condensation reaction, with elimination of HCl.
What type of reaction forms an amide from an acyl chloride and ammonia?
A condensation reaction — the acyl chloride and ammonia join together, eliminating HCl to form an amide.
True or False?
The reaction of propanoyl chloride with a primary amine produces a non-substituted amide.
False.
A primary amine produces a substituted amide. Only the reaction with ammonia gives a non-substituted amide.
When propanoyl chloride reacts with excess ammonia, the products are .......... and .......... .
When propanoyl chloride reacts with excess ammonia, the products are propanamide and ammonium chloride.
Why is the carbonyl carbon of an acyl chloride susceptible to nucleophilic attack?
The electronegative chlorine atom withdraws electron density from the carbonyl carbon, making it electron-deficient and vulnerable to attack by nucleophiles such as the lone pair on nitrogen in ammonia or amines.
Define polyamide.
A polyamide is a condensation polymer in which repeating units are joined by amide (–CO–NH–) links, formed from diamine and dicarboxylic acid (or dioyl dichloride) monomers.
What are the monomers used to make Nylon-6,6?
Nylon-6,6 is made from 1,6-diaminohexane and hexane-1,6-dioic acid. The '6,6' name reflects the six carbon atoms in each monomer.
True or False?
Kevlar's strength arises from the many hydrogen bonds between its polymer chains.
True.
The neatly arranged chains in Kevlar form extensive hydrogen bonds, producing a strong, flexible, and fire-resistant material used in bullet-proof vests.
Define condensation polymer.
A condensation polymer is a polymer formed by repeated condensation reactions between monomers, with elimination of a small molecule (such as water or HCl), joining units via ester or amide bonds.
What two monomer types react to form a polyester?
A dicarboxylic acid (containing two –COOH groups) and a diol (containing two –OH groups) react together, forming ester links with elimination of water.
True or False?
All natural condensation polymers are formed by elimination of water.
True.
Natural condensation polymers (such as proteins and polysaccharides) are always formed by elimination of water during polymerisation.
Condensation polymers can be identified because their monomers are linked by .......... or .......... bonds.
Condensation polymers can be identified because their monomers are linked by ester or amide bonds.
What is a hydroxycarboxylic acid monomer, and what polymer does it form?
A hydroxycarboxylic acid is a single monomer containing both an –OH group and a –COOH group. It can self-condense to form a polyester, with water eliminated at each step.
What is PET (poly(ethylene terephthalate))?
PET is a polyester condensation polymer formed from ethane-1,2-diol and benzene-1,4-dicarboxylic acid, with water eliminated at each ester link. It is also known by the brand names Terylene and Dacron.
What monomers can be used instead of dicarboxylic acids to make polyamides, and why?
Dioyl dichlorides (containing two –COCl groups) can replace dicarboxylic acids. They are more reactive monomers but are more expensive.
True or False?
Amino acids can act as monomers for condensation polymerisation.
True.
Amino acids contain both an –NH2 and a –COOH group, allowing them to condense with one another to form polypeptides via amide (peptide) bonds.
Name three types of monomer combinations that can produce a condensation polymer.
Dicarboxylic acid + diol → polyester
Dicarboxylic acid + diamine → polyamide
Amino acids → polypeptide/protein
Define zwitterion.
A zwitterion is an ion that carries both a positive charge (H3N+) and a negative charge (COO-) within the same molecule, formed by intramolecular proton transfer in an amino acid.
How does the zwitterion respond when a small amount of acid is added to an amino acid solution?
The COO- group accepts an H+ ion to reform the –COOH group, converting the zwitterion into a positively charged ion. This is how amino acid solutions resist pH change and act as buffer solutions.
True or False?
All 2-amino acids are optically active.
False.
Glycine is the exception: its central carbon bears two hydrogen atoms (CH2 group) rather than four different groups, so it has no chiral centre and is not optically active.
Define isoelectric point.
The isoelectric point is the pH at which an amino acid exists predominantly as the neutral zwitterion, with no net overall charge, because neither positively nor negatively charged ions dominate.
The general formula of an amino acid is .......... where R represents the unique side chain.
The general formula of an amino acid is H2N–CHR–COOH where R represents the unique side chain.
What is hydrolysis of a protein, and what conditions are required?
Hydrolysis of a protein is the breaking of peptide bonds by prolonged heating with concentrated hydrochloric acid. The acidic environment causes the amino acids released to have their –NH2 groups protonated as +NH3 groups.
Define peptide bond.
A peptide bond is an amide bond (–CO–NH–) formed between the –COOH group of one amino acid and the –NH2 group of another in a condensation reaction, with elimination of water.
True or False?
Amino acids can be separated by chromatography based on their size.
False.
Amino acids are separated by chromatography based on their relative solubilities in the mobile and stationary phases, not their size.
Why are amino acids described as soluble crystalline solids?
Because they exist as zwitterions with both positive (H3N+) and negative (COO-) charges, creating strong intermolecular forces of attraction between amino acid molecules.
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