Introduction to Organic Chemistry (Edexcel A Level Chemistry): Flashcards

In a homologous series, each successive member differs by CH₂, all members share the same functional group.

Physical properties such as boiling point change gradually up the series.

Ethanol and propanol belong to the same homologous series because they share the same functional group (the hydroxyl group, -OH) and propanol differs from ethanol by exactly one CH₂ unit.

Functional groups are atoms or groups of atoms within organic molecules that determine the physical and chemical properties of those molecules.

False.

Members of a homologous series have similar chemical properties (due to the same functional group), not identical ones — for example, reactivity can vary with chain length. Physical properties such as boiling point and density also change gradually up the series.

A homologous series is defined by: the same functional group, the same general formula, similar chemical properties, and each successive member differing by one CH₂ unit.

False.

In functional group notation, R represents an alkyl group — a carbon chain such as CH₃– (methyl) or C₂H₅– (ethyl). Hydrogen atoms are not alkyl groups and are not represented by R.

As a homologous series is ascended, the size of the molecule increases by one CH₂ unit each time, which increases intermolecular forces, causing gradual changes in physical properties such as boiling point and density.

Systematic nomenclature is a set of IUPAC rules used to name organic compounds, where the stem of each name indicates the number of carbon atoms in the longest chain and prefixes or suffixes indicate any functional groups or side-chains.

When numbering a carbon chain for IUPAC naming, start from the end that gives the lowest possible numbers.

If there are two identical side-chains, add the prefix di-.

If two different side-chains are present, list them in alphabetical order.

An alkyl group is a hydrocarbon side-chain formed by removing one hydrogen atom from an alkane, named by adding the suffix -yl to the alkane stem (for example, methyl, ethyl).

These prefixes indicate the number of carbon atoms in the longest chain: meth- = 1, eth- = 2, prop- = 3, but- = 4. They form the basis of IUPAC nomenclature for organic compounds.

An addition reaction is an organic reaction in which two or more molecules combine to give a single product with no other products.

True.

In organic chemistry, oxidation often refers to the addition of oxygen or removal of hydrogen atoms. The symbol [O] is used to represent one oxygen atom from an oxidising agent.

An elimination reaction is a reaction in which a small molecule (such as H₂O or HCl) is removed from an organic molecule.

In a substitution reaction, one atom or group is replaced by another atom or group. In a hydrolysis reaction, a compound is broken down by water (or dilute acid or alkali) into simpler products.

A condensation reaction is a reaction in which two organic molecules join together and in the process eliminate a small molecule such as H₂O or HCl.

Structural isomers are compounds that have the same molecular formula but different structural formulae, meaning their atoms are connected in different arrangements.

False.

Pentane and 2,2-dimethylpropane are chain isomers, not positional isomers. Both have the molecular formula C₅H₁₂, but differ in the length of the longest carbon chain: 5 in pentane, 3 in 2,2-dimethylpropane.

Chain isomerism is a type of structural isomerism in which compounds have the same molecular formula but different lengths of longest hydrocarbon chain, caused by branching.

For Edexcel A Level Chemistry, you must be able to identify three types of structural isomerism:

1. Chain isomerism — same molecular formula, different length of longest carbon chain (caused by branching)

2. Positional isomerism — same molecular formula and chain, but the functional group is on a different carbon

3. Functional group isomerism — same molecular formula but different functional groups (e.g. alcohols vs ethers; aldehydes vs ketones)

Positional isomerism is a type of structural isomerism in which the molecular formula and carbon chain length are the same, but the functional group is located on different carbon atoms.

Structural isomers share the same molecular formula.

Chain isomers differ in the length of the longest carbon chain.

Positional isomers differ in the position of the functional group.

True.

Butan-1-ol and butan-2-ol are positional isomers — a type of structural isomerism. They share the molecular formula C₄H₁₀O but the hydroxyl group is on carbon 1 in one and carbon 2 in the other.

The first step is to confirm that both compounds have the same molecular formula. If the molecular formulae differ, the compounds cannot be structural isomers (or any type of isomer).

Stereoisomers are compounds that have the same atoms connected to each other in the same order, but with those atoms arranged differently in space, giving them different chemical and physical properties.

In E/Z isomerism, Z isomers have the highest priority groups on the same side of the double bond.

E isomers have the highest priority groups on opposite sides of the double bond.

The E/Z system applies when each carbon of the C=C has two different groups attached to it.

E/Z isomerism is a type of stereoisomerism seen in unsaturated (double bond containing) or ring compounds that have the same molecular formula and same connectivity of atoms, but different spatial arrangements around the restricted bond.

E/Z isomerism requires: (1) a C=C double bond (or a ring structure) that restricts rotation, and (2) two different groups attached to each carbon of the double bond so that distinct spatial arrangements are possible.

False.

The cis/trans naming system cannot be used when three or four different groups are attached to the C=C bond. In such cases, the E/Z naming system based on CIP priority rules must be used instead.

E comes from the German word entgegen (meaning opposite) — the highest priority groups are on opposite sides of the double bond. Z comes from zusammen (meaning together) — the highest priority groups are on the same side.

Cahn-Ingold-Prelog (CIP) priority rules are used to assign E or Z labels to stereoisomers by comparing the atomic number of the first atom attached to each carbon of the double bond: the higher the atomic number, the higher the priority.

False.

E/Z isomers have different physical and chemical properties. For example, they may have different melting points or boiling points (physical) and different reaction rates for the same reaction (chemical).

The term geometric isomerism is no longer in use in current Edexcel specifications. It has been replaced by E/Z isomerism, which is a more precise system that works even when all four substituents on the C=C are different.