A key concept is the homologous series, which is a “family” of organic compounds that share the same general formula and similar chemical properties. Each member of the series differs from the next by a -CH₂- group.

Crude Oil and Hydrocarbons

Crude oil is a thick, black, sticky liquid found in rocks deep underground. It’s a finite resource, meaning it will eventually run out, because it was formed over millions of years from the remains of ancient biomass, mainly tiny sea creatures like plankton.

Crude oil isn’t a single substance; it’s a complex mixture of thousands of different compounds. The vast majority of these compounds are hydrocarbons.

A hydrocarbon is a compound made up of hydrogen and carbon atoms only.

Exam Tip: The definition of a hydrocarbon is one of the most important facts in this topic. You must remember that they contain only hydrogen and carbon. If a compound contains oxygen (like ethanol, C₂H₅OH), it is not a hydrocarbon.

Alkanes: The Simplest Hydrocarbons

Most of the hydrocarbons in crude oil are part of a homologous series called the alkanes.

Alkanes are known as saturated hydrocarbons. “Saturated” means that all the bonds between the carbon atoms are single covalent bonds. This makes them relatively unreactive.

The general formula for the alkane family is CₙH₂ₙ₊₂. This means for ‘n’ carbon atoms, you will have ‘2n+2’ hydrogen atoms.

You need to know the first four members of the alkane series:

Exam Tip: You must be able to recall the names and formulas of the first four alkanes. A good way to remember the order of the prefixes is: Monkeys Eat Peanut Butter. You also need to be able to draw their displayed formulas, showing all atoms and single covalent bonds.

Crude oil is a messy mixture of thousands of different hydrocarbons. To make it useful, we need to separate it into simpler, more manageable groups called fractions. This separation process is called fractional distillation.

How Fractional Distillation Works

Fractional distillation separates hydrocarbons based on their different boiling points. The process works like this:

1. Heating: The crude oil is heated in a furnace to a very high temperature (around 350°C), causing most of the hydrocarbons to evaporate and turn into a gas.

2. Entering the Column: The mixture of hot liquid and gas is pumped into the bottom of a tall tower called a fractionating column.

3. Temperature Gradient: The column has a temperature gradient – it’s very hot at the bottom and gets progressively cooler towards the top.

4. Rising and Condensing: The hot hydrocarbon gases rise up the column. As they rise, they cool down.

5. Collection: Different hydrocarbons will condense back into liquids at different temperatures (and therefore at different levels) in the column. When a substance condenses, it is collected on trays.

The fractions are collected as follows:

• • Short-chain hydrocarbons have low boiling points. They rise a long way up the column before they condense and are collected near the top.

  • Long-chain hydrocarbons have high boiling points. They condense and are collected near the bottom of the column.

  • Some substances have very low boiling points and remain as gases, even at the top of the column. These are collected as refinery gases.

  • Some substances have very high boiling points and do not evaporate at all. They remain at the bottom as a thick, gooey residue.

Exam Tip: You must be able to describe the process of fractional distillation. Key terms you need to use are: evaporation, condensation, temperature gradient, and boiling point. Remember that separation depends on the different boiling points of the hydrocarbons.

Properties of Hydrocarbon Fractions

The physical properties of hydrocarbons change depending on the size of their molecules (the length of the carbon chain).

As the hydrocarbon chain length increases:

Exam Tip: A common question asks you to compare the properties of two fractions, for example, petrol (gasoline) and bitumen (asphalt). Petrol has smaller molecules, so it has a lower boiling point, is less viscous (runnier), and is much more flammable than bitumen, which has very large molecules.

Petrochemicals

The fractions from crude oil are incredibly useful. Some are used directly as fuels (like petrol, diesel, and kerosene). Others are used as a feedstock for the petrochemical industry.

A feedstock is a raw material that is used to manufacture other chemicals. The petrochemical industry uses hydrocarbons from crude oil to make a vast array of useful products, including:

• Polymers (plastics)

• Solvents

• Lubricants

• Detergents

• Fertilisers

The ability of carbon atoms to form strong bonds and create families of similar compounds is the reason why so many different materials can be made from this single raw material.

The way a hydrocarbon behaves—whether it’s a gas or a thick liquid, and how easily it burns—depends almost entirely on the size of its molecules.

Physical Properties 

As the length of the carbon chain in a hydrocarbon molecule increases, its physical properties change in a predictable way.

Exam Tip: A common exam question will ask you to compare two fractions, like gasoline (petrol) and lubricating oil. You should state that gasoline has smaller molecules, therefore it has a lower boiling point, is less viscous (runnier), and is more flammable than lubricating oil.

Chemical Properties: Combustion 

The most important chemical property of hydrocarbons is that they burn. This combustion reaction releases a large amount of energy, which is why we use them as fuels.

Complete Combustion

Complete combustion happens when there is plenty of oxygen. The hydrocarbon burns completely to produce only two products: carbon dioxide and water.

General equation: Hydrocarbon + Oxygen ⟶ Carbon Dioxide + Water

For example, the complete combustion of methane (CH₄): CH₄(g) + 2O₂(g) ⟶ CO₂(g) + 2H₂O(l)

Incomplete Combustion

Incomplete combustion happens when there is a limited supply of oxygen. This is a “dirtier” type of burning that produces harmful products.

Instead of just CO₂ and water, incomplete combustion can produce:

• Carbon Monoxide (CO): A toxic, colorless, and odorless gas.

• Carbon (C): Released as soot (black particles), which can cause breathing problems and global dimming.

Exam Tip: You must be able to write and balance symbol equations for the complete combustion of different alkanes. Remember to balance the carbons first, then the hydrogens, and finally the oxygens.

Alkanes vs. Alkenes

Hydrocarbons can be sorted into different families. The two most important at GCSE are alkanes and alkenes.

• Alkanes are saturated. This means they only have single carbon-carbon bonds (C-C). Because these bonds are strong, alkanes are relatively unreactive.

• Alkenes are unsaturated. This means they have at least one double carbon-carbon bond (C=C). This double bond makes alkenes more reactive than alkanes.

During fractional distillation, we get more long-chain hydrocarbons than we need and not enough of the more useful short-chain ones. Cracking is the industrial process that solves this problem by breaking down large, less useful hydrocarbon molecules into smaller, more valuable ones.

Why Do We Need Cracking?

There is a high demand for short-chain hydrocarbons like petrol for cars and kerosene for jet fuel. However, the supply of these fractions from crude oil is often not enough. Conversely, there is a low demand for long-chain fractions like fuel oil.

Cracking converts the low-demand, long-chain alkanes into high-demand, short-chain alkanes and alkenes.

Example: The long-chain alkane, decane, can be cracked to produce octane (a component of petrol) and ethene (used to make plastics). C₁₀H₂₂ ⟶ C₈H₁₈ + C₂H₄

Exam Tip: Remember the economic reason for cracking: the supply of long-chain fractions is greater than demand, while the demand for short-chain fractions is greater than the supply. Cracking fixes this imbalance.

Methods of Cracking

There are two main methods for cracking hydrocarbons:

1. Catalytic Cracking: The hydrocarbons are heated to a high temperature (around 470 – 550 °C) to vaporise them. The hot gases are then passed over a hot, powdered catalyst, such as aluminium oxide.

2. Steam Cracking: The hydrocarbons are mixed with steam and heated to an even higher temperature.

Both methods cause the strong covalent bonds in the large molecules to break, forming smaller molecules.

Exam Tip: When writing a cracking equation, the reactant is always a large alkane. The products are always a smaller alkane and at least one alkene. Make sure you obey the law of conservation of mass – the number of carbon and hydrogen atoms must be the same on both sides of the arrow.

Alkenes: The Useful By-product

Cracking always produces a type of hydrocarbon called an alkene. Alkenes are very important in the chemical industry.

• Structure: Alkenes are hydrocarbons that contain at least one carbon-carbon double bond (C=C). This double bond is their functional group.

• Unsaturated: Because of this double bond, alkenes are described as unsaturated. This means they have the potential to bond with more atoms. They are more reactive than alkanes.

• General Formula: The general formula for the alkene homologous series is CₙH₂ₙ.

The first three alkenes you need to know are ethene (C₂H₄), propene (C₃H₆), and butene (C₄H₈).

Test for Alkenes

We can test for the presence of the C=C double bond (and therefore, tell the difference between an alkane and an alkene) using bromine water.

• Procedure: Add a few drops of orange bromine water to the hydrocarbon and shake.

• Result with an Alkane (saturated): The solution will remain orange. No reaction occurs.

• Result with an Alkene (unsaturated): The solution will turn from orange to colourless. The alkene reacts with the bromine in an addition reaction, breaking the double bond.

Exam Tip: The bromine water test is a crucial piece of knowledge. You must remember the starting colour (orange) and the positive result for an alkene (colourless). A common mistake is to say “clear” instead of “colourless.” “Clear” means transparent, but a colourless liquid can still be transparent.

Alkenes are another important homologous series of hydrocarbons. They are produced during the cracking of long-chain alkanes and are the starting point for making many useful chemicals, including plastics.

Definition and General Formula

Alkenes are defined by a key structural feature: they contain at least one carbon-carbon double bond (C=C). This double bond is the functional group of alkenes, meaning it’s the part of the molecule that is responsible for most of their chemical reactions.

The general formula for the alkene homologous series is CₙH₂ₙ.

Exam Tip: You must know the general formula for alkenes (CₙH₂ₙ) and be able to contrast it with the general formula for alkanes (CₙH₂ₙ₊₂).

Unsaturated Hydrocarbons

Because they have a C=C double bond, alkenes are known as unsaturated hydrocarbons. This means they contain two fewer hydrogen atoms than the alkane with the same number of carbon atoms and have the potential to bond with more atoms by breaking the double bond.

For example:

• Propane (an alkane) has the formula C₃H₈.

• Propene (an alkene) has the formula C₃H₆.

Exam Tip: Remember: Alkanes are saturated with single bonds. Alkenes are unsaturated with at least one double bond. The bromine water test can distinguish between them.

Members of the Alkene Series

You need to know the first few members of the alkene series. Note that there is no “methene” because you need at least two carbon atoms to form a C=C double bond.

The first four alkenes are:

• Ethene (C₂H₄)

• Propene (C₃H₆)

• Butene (C₄H₈)

• Pentene (C₅H₁₀)

Reactivity and Importance

The presence of the C=C double bond makes alkenes much more reactive than alkanes. This reactivity makes them extremely useful as a feedstock (raw material) in the chemical industry, particularly for making polymers. For example, ethene is the monomer used to make poly(ethene), a common plastic.

Alkenes are significantly more reactive than alkanes. This is all because of their functional group: the carbon-carbon double bond (C=C). This double bond is an area of high electron density, making it a target for chemical attack and allowing alkenes to undergo reactions that alkanes cannot.

Addition Reactions

The most important type of reaction for alkenes is the addition reaction. In this process, the C=C double bond breaks open, and a new atom (or group of atoms) is added to each of the two carbon atoms. The molecule changes from being unsaturated (with a double bond) to saturated (with only single bonds).

1. Reaction with Hydrogen (Hydrogenation)

When an alkene reacts with hydrogen gas (H₂) in the presence of a catalyst, the double bond breaks, and a hydrogen atom adds to each carbon. This turns the unsaturated alkene into a saturated alkane.

Example: Ethene reacts with hydrogen to form ethane. C₂H₄ + H₂ ⟶ C₂H₆

2. Reaction with Water (Hydration)

Alkenes can react with water (in the form of steam) under high temperature and pressure, with a catalyst. This addition reaction forms an alcohol. An H atom from the water adds to one carbon, and an OH group adds to the other.

Example: Ethene reacts with steam to form ethanol. C₂H₄ + H₂O ⟶ C₂H₅OH

3. Reaction with Halogens

Alkenes readily react with halogens like bromine (Br₂) and chlorine (Cl₂). The double bond breaks, and a halogen atom adds to each carbon, forming a haloalkane.

Example: Ethene reacts with bromine to form 1,2-dibromoethane. C₂H₄ + Br₂ ⟶ C₂H₄Br₂

This reaction is the basis for the bromine water test.

Exam Tip: You must be able to draw the displayed formula for the products of these addition reactions. Remember to break the C=C double bond and add the new atoms to those two carbons, ensuring every carbon atom has a total of four single bonds.

Combustion Reactions 

Like all hydrocarbons, alkenes burn in oxygen.

• Complete Combustion: With plenty of oxygen, alkenes burn to produce carbon dioxide and water.

• Incomplete Combustion: In a limited supply of oxygen, alkenes undergo incomplete combustion. They tend to burn with smoky yellow flames, producing soot (carbon) and toxic carbon monoxide gas.

Exam Tip: The smoky flame is a key observation. If you are asked to distinguish between an alkane and an alkene by burning them, the alkene is the one that produces more soot and a smokier flame.

Alcohols are a homologous series of organic compounds that are widely used as solvents, fuels, and in drinks. Their properties are all determined by their special functional group.

Structure and Members of Alcohols

Alcohols are organic molecules that contain the hydroxyl functional group (-OH).

The first four members of the alcohol homologous series are essential to know:

• Methanol (CH₃OH)

• Ethanol (C₂H₅OH)

• Propanol (C₃H₇OH)

• Butanol (C₄H₉OH)

Exam Tip: You need to be able to recognise alcohols from their name (ending in ‘-ol’) or from their formula, identified by the -OH group. Be careful not to confuse the hydroxyl group (-OH) with the hydroxide ion (OH⁻) found in alkalis.

Reactions of Alcohols

Alcohols undergo several important reactions:

1. Combustion: Alcohols are flammable and burn completely in a plentiful supply of oxygen to produce carbon dioxide and water.

   • Ethanol + Oxygen ⟶ Carbon Dioxide + Water

   • C₂H₅OH + 3O₂ ⟶ 2CO₂ + 3H₂O

2. Reaction with Sodium: Alcohols react with sodium metal. The reaction produces bubbles of hydrogen gas and a salt called a sodium alkoxide.

   • Sodium + Ethanol ⟶ Sodium Ethoxide + Hydrogen

3. Oxidation: Alcohols can be oxidised by reacting with an oxidising agent to form carboxylic acids. For example, ethanol oxidises to form ethanoic acid. This is what happens when wine is left open to the air and turns sour like vinegar.

4. Dissolving in Water: The first four alcohols dissolve completely in water to form neutral solutions with a pH of 7.

Exam Tip: For the reaction with sodium, the key observation is the fizzing (effervescence) which is the hydrogen gas being produced.

Production of Ethanol by Fermentation

Ethanol for alcoholic drinks and industrial use can be made by fermentation. This process uses yeast to turn sugars into ethanol.

The word equation is: Sugar ⟶ Ethanol + Carbon Dioxide

Fermentation requires very specific conditions:

• Yeast: Provides the enzymes that act as a catalyst.

• Anaerobic conditions: There must be no oxygen. If oxygen is present, the ethanol will oxidise into ethanoic acid (vinegar).

• Temperature: The temperature must be kept between 25°C and 45°C. If it’s too cold the reaction is too slow, and if it’s too hot the enzymes in the yeast will be denatured.

Uses of Alcohols

Alcohols are very useful chemicals:

• Fuels: They can be burned to release energy and are sometimes mixed with petrol.

• Solvents: Ethanol is a good solvent used in perfumes, aftershaves, and medicines because it can dissolve substances that water can’t.

• Alcoholic Drinks: Ethanol is the alcohol found in beer, wine, and spirits.

Carboxylic acids are another important homologous series in organic chemistry. They are found in nature (for example, in vinegar and citrus fruits) and are known for their distinctively sour taste and smell.

Structure and Members of the Series

Carboxylic acids are organic molecules that contain the carboxyl functional group (-COOH). This group consists of a carbon atom double-bonded to one oxygen atom and single-bonded to another oxygen atom, which is part of a hydroxyl group.

You need to know the first four members of the carboxylic acid series:

• Methanoic acid (HCOOH)

• Ethanoic acid (CH₃COOH)

• Propanoic acid (C₂H₅COOH)

• Butanoic acid (C₃H₇COOH)

Exam Tip: You can identify a carboxylic acid from its name, which ends in ‘-anoic acid’, or its formula, which will always show the -COOH group.

Chemical Properties as Acids

Carboxylic acids behave as weak acids when they dissolve in water. This means they do not fully release their hydrogen ions.

• Partial Ionisation: When a carboxylic acid dissolves in water, only a small proportion of the molecules ionise (split up) to release H⁺ ions. This is a reversible reaction.

  CH₃COOH(aq) ⇌ CH₃COO⁻(aq) + H⁺(aq)

• Higher pH: Because they release fewer H⁺ ions into the solution than strong acids of the same concentration, carboxylic acid solutions have a higher pH (they are less acidic).

Exam Tip: A common high-level question asks you to explain the difference between a strong and a weak acid. For a weak acid like ethanoic acid, you must mention partial ionisation in water, leading to a low concentration of H⁺ ions and a higher pH.

Key Reactions

1. Reaction with Metal Carbonates: Carboxylic acids react with metal carbonates in a typical acid-carbonate reaction to produce a salt, water, and carbon dioxide.

   • Ethanoic acid + Sodium carbonate ⟶ Sodium ethanoate + Water + Carbon dioxide

   • The production of carbon dioxide gas causes fizzing and can be confirmed by bubbling the gas through limewater, which would turn cloudy.

2. Reaction with Alcohols (Esterification): This is a key reaction used to make esters.

   • Carboxylic acids react with alcohols in the presence of a strong acid catalyst (like sulfuric acid) to form an ester and water.

   • Esters are known for their pleasant, fruity smells and are used in perfumes and food flavourings.

   • Example: Ethanoic acid reacts with ethanol to produce the ester ethyl ethanoate and water.

Exam Tip: You need to know the reaction to form ethyl ethanoate. Remember the general pattern: Carboxylic Acid + Alcohol ⟶ Ester + Water. The name of the ester comes from the alcohol first (ethanolbecomes ethyl) and the carboxylic acid second (ethanoic acid becomes ethanoate).

Polymers are very large, long-chain molecules that are essential to modern life—they form the basis of plastics, fabrics, and many other materials. They are made by joining lots of small, reactive molecules together in a process called polymerisation.

What is Addition Polymerisation?

Polymers are long-chain molecules made up of many repeating units. The small molecules that join together to form the polymer are called monomers.

Addition polymerisation is the process where many monomer molecules join together to form a polymer with no loss of any atoms or molecules. The polymer is the only product. This process typically requires high pressures and a catalyst.

Exam Tip: The key feature of addition polymerisation is that nothing is lost. The empirical formula of the monomer and the repeating unit of the polymer are identical.

The Monomer Requirement: A C=C Double Bond

For addition polymerisation to happen, the monomer must be unsaturated. This means it must have a carbon-carbon double bond (C=C). Alkenes are the perfect monomers for this process.

Here’s how it works:

1. The high pressure and catalyst cause the C=C double bond in each monomer to break open.

2. This leaves each carbon atom with a spare, unbonded electron.

3. The monomers then join end-to-end, forming a long, saturated chain held together by single bonds. The final polymer chain has no double bonds.

From Ethene to Poly(ethene)

The simplest example is the polymerisation of ethene to make poly(ethene), commonly known as polythene.

1. Many ethene monomers, each with a C=C double bond, are subjected to high pressure and a catalyst.

2. The double bond in each ethene molecule opens up.

3. The monomers link together to form a long saturated polymer chain.

Exam Tip: You must be able to draw the repeating unit of a polymer given its monomer. To do this:

1. Change the C=C double bond in the monomer to a C-C single bond.

2. Draw single bonds extending out from the ends of the unit.

3. Put the whole repeating unit in square brackets and add a small ‘n’ at the bottom right to show it repeats many times.

Naming and Examples

The name of an addition polymer is simply “poly-” followed by the name of the monomer in brackets.

Different monomers create polymers with different repeating units and therefore different properties, making them suitable for a wide range of uses.

While addition polymerisation builds long chains by simply adding monomers together, condensation polymerisation is a different process where monomers join together and a small molecule is lost, or “condensed out,” each time a link is formed.

Definition and Process

Condensation polymerisation is the joining of monomers to form a polymer with the elimination (loss) of a small molecule, which is usually water (H₂O).

The key differences from addition polymerisation are:

• The monomers must have two functional groups, one at each end.

• When monomers link, a small molecule (like water) is also formed. The polymer is not the only product.

Exam Tip: A common question is to state two differences between addition and condensation polymerisation. Remember: 1) Addition monomers have a C=C bond, while condensation monomers have two functional groups (like -OH or -COOH). 2) Addition has one product (the polymer), while condensation has two products (the polymer and a small molecule, e.g., water).

Making Polyesters

Polyesters are a common type of condensation polymer. They are made from two different types of monomer: a dicarboxylic acid (a molecule with a -COOH group at each end) and a diol (an alcohol with an -OH group at each end).

The carboxyl group (-COOH) of the acid monomer reacts with the hydroxyl group (-OH) of the alcohol monomer. This forms an ester link and releases one molecule of water. This process repeats, building a long polyester chain.

Making Polypeptides (Proteins)

Proteins are natural condensation polymers essential for life. The monomers that make up proteins are called amino acids.

Amino acids are unique because each monomer contains two different functional groups:

• An amino group (-NH₂)

• A carboxyl group (-COOH)

The carboxyl group of one amino acid reacts with the amino group of a neighbouring amino acid. This forms a strong peptide link and eliminates one molecule of water. As thousands of amino acids join together in this way, a long chain called a polypeptide is formed.

Other Natural Polymers

Many essential biological molecules are condensation polymers.

• Starch and Cellulose: These are polymers made from sugar monomers (like glucose).

• DNA: Deoxyribonucleic acid is a polymer made from monomers called nucleotides.

Exam Tip: You must be able to state the monomers for the key natural polymers: proteins are made from amino acids, and starch/cellulose are made from sugars.

Amino acids are the essential building blocks of life. They are the monomers that join together to create proteins, which carry out countless vital functions in all living organisms.

Structure of Amino Acids

Amino acids are unique monomers because each molecule contains two different functional groups:

• An amino group (−NH2​), which is basic.

• A carboxyl group ($-COOH$), which is acidic.

There are about 20 common, naturally occurring amino acids. They all share this same basic structure but differ in their side chain (often represented by ‘R’). Glycine is the simplest amino acid.

Exam Tip: You must be able to identify the two functional groups (-NH₂ and -COOH) on a diagram of an amino acid.

Forming Polypeptides

Amino acids join together to form long chains called polypeptides. This happens through condensation polymerisation.

• Mechanism: The carboxyl group (-COOH) of one amino acid reacts with the amino group (-NH₂) of another.

• Linkage: A strong covalent bond called a peptide bond is formed between the monomers.

• By-product: For every peptide bond formed, one molecule of water (H₂O) is eliminated (lost).

Because water is lost, this is a condensation reaction.

Exam Tip: Be prepared to draw a diagram showing how two simple amino acids (like glycine) join together. You need to show the peptide bond clearly and indicate that a water molecule is formed.

What are Proteins?

Proteins are polymers made from one or more long chains of polypeptides. The sequence of different amino acids in the chain is crucial—it determines how the chain folds into a unique 3D shape. This specific shape allows the protein to do its specific job.

Proteins are vital biological molecules and include:

• Enzymes: Biological catalysts.

• Haemoglobin: The protein that carries oxygen in the blood.

• Tissues: Proteins make up muscles, tendons, hair, and nails.

Nature is the original master of polymer chemistry. Many of the most complex and important molecules for life are natural polymers, built from repeating monomer units.

DNA (Deoxyribonucleic Acid)

DNA is a massive polymer molecule that is essential for life. It carries the genetic instructions for the development and functioning of all living organisms.

The Structure of DNA

DNA has a very specific and famous structure:

• It is made of two polymer chains coiled together to form a double helix.

• The monomers that make up DNA are called nucleotides.

• There are four different types of nucleotide monomers used to build the chains.

Each nucleotide is made of three parts: a phosphate group, a deoxyribose sugar, and a base. The sugar and phosphate groups join together to form the “sugar-phosphate backbone” of each polymer chain. It is the base that makes each of the four nucleotides different. The four bases are Adenine (A), Thymine (T), Cytosine (C), and Guanine (G).

The genetic code is stored in the specific sequence of these bases along the DNA chains.

Exam Tip: You must be able to state that DNA is a polymer made from four different nucleotide monomers and describe its shape as a double helix.

Other Naturally Occurring Polymers

Besides DNA, there are other vital polymers found in nature. You need to know what monomers they are made from.

1. Proteins: These are condensation polymers made from amino acid monomers. Proteins have a huge range of functions, acting as enzymes and forming body tissues.

2. Starch and Cellulose: These are both large carbohydrates that are polymers made from glucose (a type of sugar) monomers. Starch is used for energy storage, and cellulose provides structural support in plant cell walls.

Below are some of the fundamental monomer building blocks for these natural polymers.

Exam Tip: It is essential to remember the monomer for each key biological polymer.

Proteins → Amino Acids

Starch / Cellulose → Glucose (Sugars)

DNA → Nucleotides