One Small Group of Atoms Decides How a Whole Molecule Behaves
Spot the functional group in a carbon compound and name its family, use a homologous series to predict the next member, name a compound by the IUPAC rules, and tell combustion, oxidation, addition and substitution apart.
Why do two compounds with the same carbon chain behave completely differently?
Take three compounds, each with two carbon atoms.
- Ethane is an unreactive gas used as a fuel
- Ethanol is a liquid that dissolves in water, reacts with sodium, and can be oxidised
- Ethanoic acid is a liquid that turns blue litmus red and fizzes with baking soda
The carbon skeleton is the same in all three. What differs is a small group of atoms attached to it — nothing in ethane, an -OH group in ethanol, a -COOH group in ethanoic acid.
That attached group is called the functional group, and it carries essentially all the chemistry. The hydrocarbon part is a stable, unreactive framework; the functional group is where reactions happen. So the whole of organic chemistry can be organised by functional group rather than by chain length, and that is exactly what this part of the chapter does.
Once compounds are grouped that way, two more things become possible. Compounds with the same functional group form a homologous series whose members differ in a completely regular way, so you can predict a compound you have never met. And a naming system — IUPAC nomenclature — can describe any structure in a single word, and reconstruct the structure from that word.
This page covers the second part of the CBSE Class 10 Science chapter on carbon and its compounds: functional groups, homologous series, IUPAC naming, and the four types of reaction.
- Ethane is an unreactive gas used as a fuel
- Ethanol is a liquid that dissolves in water, reacts with sodium, and can be oxidised
- Ethanoic acid is a liquid that turns blue litmus red and fizzes with baking soda
The carbon skeleton is the same in all three. What differs is a small group of atoms attached to it — nothing in ethane, an -OH group in ethanol, a -COOH group in ethanoic acid.
That attached group is called the functional group, and it carries essentially all the chemistry. The hydrocarbon part is a stable, unreactive framework; the functional group is where reactions happen. So the whole of organic chemistry can be organised by functional group rather than by chain length, and that is exactly what this part of the chapter does.
Once compounds are grouped that way, two more things become possible. Compounds with the same functional group form a homologous series whose members differ in a completely regular way, so you can predict a compound you have never met. And a naming system — IUPAC nomenclature — can describe any structure in a single word, and reconstruct the structure from that word.
This page covers the second part of the CBSE Class 10 Science chapter on carbon and its compounds: functional groups, homologous series, IUPAC naming, and the four types of reaction.
Which functional group belongs to which family?
Five functional groups cover the whole of the Class 10 syllabus. Learn the group, its family name and one example of each.
- Halogen, written or — a halogen derivative such as chloroethane,
- Alcohol, written — an alcohol such as ethanol,
- Aldehyde, written — an aldehyde such as ethanal,
- Ketone, written with carbon on both sides — a ketone such as propanone,
- Carboxylic acid, written — a carboxylic acid such as ethanoic acid,
Worked example 1. Identify the functional group in and name the family.
The group at the end is , so it is an alcohol — propanol, with three carbons.
Worked example 2. Identify the family of .
The group makes it a carboxylic acid. Note that this group contains both a double-bonded oxygen and an , and it behaves as neither an aldehyde nor an alcohol — the combination is a new group with its own chemistry, which is why it turns litmus red while ethanol does not.
Worked example 3 — the pair that is most often confused. Distinguish from .
Both contain a carbon double-bonded to oxygen. The difference is what else that carbon is attached to:
- In an aldehyde it carries a hydrogen — so is ethanal
- In a ketone it sits between two carbon atoms — so is propanone
Count what the carbonyl carbon is bonded to and the two families never get mixed up.
A functional group replaces a hydrogen, it is not added on top of one. Ethane is ; ethanol is , with five hydrogens on the carbons and one in the . The total hydrogen count went from six to six, not to seven. So the carbon still has exactly four bonds, and checking that is the fastest way to spot an impossible structure.
Why the group matters more than the chain. Every alcohol reacts with sodium to release hydrogen, whether it has two carbons or twenty. Every carboxylic acid turns blue litmus red. The reactions belong to the group, which is why learning five groups is worth more than learning fifty compounds.
- Halogen, written or — a halogen derivative such as chloroethane,
- Alcohol, written — an alcohol such as ethanol,
- Aldehyde, written — an aldehyde such as ethanal,
- Ketone, written with carbon on both sides — a ketone such as propanone,
- Carboxylic acid, written — a carboxylic acid such as ethanoic acid,
Worked example 1. Identify the functional group in and name the family.
The group at the end is , so it is an alcohol — propanol, with three carbons.
Worked example 2. Identify the family of .
The group makes it a carboxylic acid. Note that this group contains both a double-bonded oxygen and an , and it behaves as neither an aldehyde nor an alcohol — the combination is a new group with its own chemistry, which is why it turns litmus red while ethanol does not.
Worked example 3 — the pair that is most often confused. Distinguish from .
Both contain a carbon double-bonded to oxygen. The difference is what else that carbon is attached to:
- In an aldehyde it carries a hydrogen — so is ethanal
- In a ketone it sits between two carbon atoms — so is propanone
Count what the carbonyl carbon is bonded to and the two families never get mixed up.
A functional group replaces a hydrogen, it is not added on top of one. Ethane is ; ethanol is , with five hydrogens on the carbons and one in the . The total hydrogen count went from six to six, not to seven. So the carbon still has exactly four bonds, and checking that is the fastest way to spot an impossible structure.
Why the group matters more than the chain. Every alcohol reacts with sodium to release hydrogen, whether it has two carbons or twenty. Every carboxylic acid turns blue litmus red. The reactions belong to the group, which is why learning five groups is worth more than learning fifty compounds.
What is a homologous series, and how do you find the next member?
**A homologous series is a family of compounds with the same functional group, in which each member differs from the previous one by a unit.
That constant difference has three consequences that questions ask about directly:
- The members share one general formula
- Consecutive members differ in molecular mass by exactly u**, since is
- Chemical properties are similar throughout, because the functional group is the same, while physical properties change gradually as the chain lengthens
Worked example 1 — the alkanes. Compute the molecular masses of the first four members, using C and H :
**The differences are , and — constant, as the definition requires.
Worked example 2 — the alcohols.**
Again and . **The u gap is the signature of a homologous series, and a question giving you two consecutive masses is really giving you a check.
Worked example 3 — predicting the next member.** The third member of the aldehyde series is propanal, . What is the fourth, and what is its molecular mass?
Add one : the fourth member is butanal, . Its mass is the propanal mass plus :
Check directly: is , which is , as required.
The general formulas worth having.
- Alkanes , alkenes , alkynes
- Alcohols
- Aldehydes
- Carboxylic acids
How the physical properties drift. Melting and boiling points rise along a series as the molecules get bigger and the forces between them grow. Solubility in water falls, because the hydrocarbon part grows while the functional group stays the same size. That is why methanol and ethanol mix freely with water while a long-chain alcohol barely dissolves at all — and why the first few members of a series are gases, the middle ones liquids and the later ones solids.
The distinction to keep clear. Homologues have the same functional group and different formulas; isomers have the same formula and different structures. Ethanol and propanol are homologues; ethanol and dimethyl ether are isomers — and a question asking for one will not accept the other.
That constant difference has three consequences that questions ask about directly:
- The members share one general formula
- Consecutive members differ in molecular mass by exactly u**, since is
- Chemical properties are similar throughout, because the functional group is the same, while physical properties change gradually as the chain lengthens
Worked example 1 — the alkanes. Compute the molecular masses of the first four members, using C and H :
**The differences are , and — constant, as the definition requires.
Worked example 2 — the alcohols.**
Again and . **The u gap is the signature of a homologous series, and a question giving you two consecutive masses is really giving you a check.
Worked example 3 — predicting the next member.** The third member of the aldehyde series is propanal, . What is the fourth, and what is its molecular mass?
Add one : the fourth member is butanal, . Its mass is the propanal mass plus :
Check directly: is , which is , as required.
The general formulas worth having.
- Alkanes , alkenes , alkynes
- Alcohols
- Aldehydes
- Carboxylic acids
How the physical properties drift. Melting and boiling points rise along a series as the molecules get bigger and the forces between them grow. Solubility in water falls, because the hydrocarbon part grows while the functional group stays the same size. That is why methanol and ethanol mix freely with water while a long-chain alcohol barely dissolves at all — and why the first few members of a series are gases, the middle ones liquids and the later ones solids.
The distinction to keep clear. Homologues have the same functional group and different formulas; isomers have the same formula and different structures. Ethanol and propanol are homologues; ethanol and dimethyl ether are isomers — and a question asking for one will not accept the other.
How do you name a carbon compound using the IUPAC rules?
Count the carbons for the stem, then attach the ending that belongs to the functional group.
The stems, by number of carbon atoms:
The endings, by functional group:
- alcohol — -ol
- aldehyde — -al
- ketone — -one
- carboxylic acid — -oic acid
- halogen — added as a prefix: chloro- or bromo-
The spelling rule that carries a mark. If the ending begins with a vowel, drop the final e of -ane:
- ethane ol becomes ethanol, not ethaneol
- propane one becomes propanone
- ethane oic acid becomes ethanoic acid
But a prefix leaves the stem alone: chloro ethane stays chloroethane.
Worked examples — from structure to name.
- — two carbons, group: ethanol
- — two carbons, group: ethanal
- — three carbons, ketone group: propanone
- — two carbons, group: ethanoic acid
- — two carbons, chlorine: chloroethane
- — three carbons, at the end: propan-1-ol
Worked examples — from name to structure.
- Butanoic acid: four carbons with , so . The acid carbon is counted as one of the four
- Bromopropane: three carbons with a bromine, so
- Pentanal: five carbons with , so
The counting trap. In an aldehyde or an acid, the carbon of the or group is part of the chain. So ethanoic acid, , has two carbons in total and not three, and butanoic acid has four and not five. Count every carbon in the formula, including the one inside the functional group.
Why a number sometimes appears. When the functional group could sit at more than one position, a number says where it is — propan-1-ol has the at the end and propan-2-ol has it in the middle, and they are different compounds. The number is counted from the end nearer the group, and with only two or three carbons there is often only one possibility, so no number is needed.
And the older names still in use. Ethanol is also called ethyl alcohol, ethanoic acid is also called acetic acid, and propanone is also called acetone. Those are common names, not IUPAC names, and a question asking for the IUPAC name wants the systematic one.
The stems, by number of carbon atoms:
The endings, by functional group:
- alcohol — -ol
- aldehyde — -al
- ketone — -one
- carboxylic acid — -oic acid
- halogen — added as a prefix: chloro- or bromo-
The spelling rule that carries a mark. If the ending begins with a vowel, drop the final e of -ane:
- ethane ol becomes ethanol, not ethaneol
- propane one becomes propanone
- ethane oic acid becomes ethanoic acid
But a prefix leaves the stem alone: chloro ethane stays chloroethane.
Worked examples — from structure to name.
- — two carbons, group: ethanol
- — two carbons, group: ethanal
- — three carbons, ketone group: propanone
- — two carbons, group: ethanoic acid
- — two carbons, chlorine: chloroethane
- — three carbons, at the end: propan-1-ol
Worked examples — from name to structure.
- Butanoic acid: four carbons with , so . The acid carbon is counted as one of the four
- Bromopropane: three carbons with a bromine, so
- Pentanal: five carbons with , so
The counting trap. In an aldehyde or an acid, the carbon of the or group is part of the chain. So ethanoic acid, , has two carbons in total and not three, and butanoic acid has four and not five. Count every carbon in the formula, including the one inside the functional group.
Why a number sometimes appears. When the functional group could sit at more than one position, a number says where it is — propan-1-ol has the at the end and propan-2-ol has it in the middle, and they are different compounds. The number is counted from the end nearer the group, and with only two or three carbons there is often only one possibility, so no number is needed.
And the older names still in use. Ethanol is also called ethyl alcohol, ethanoic acid is also called acetic acid, and propanone is also called acetone. Those are common names, not IUPAC names, and a question asking for the IUPAC name wants the systematic one.
How do you tell combustion, oxidation, addition and substitution apart?
Look at what happens to the molecule: burnt completely, given extra oxygen, joined onto at a double bond, or had one atom swapped for another.
Combustion — burning in oxygen to give carbon dioxide and water, releasing heat and light.
Check the second equation: carbon and ; hydrogen and ; oxygen on the left and on the right. Saturated hydrocarbons burn with a blue flame and unsaturated ones with a sooty yellow one, as the previous part explained.
Oxidation — adding oxygen without burning, using an oxidising agent. An alcohol becomes a carboxylic acid:
Alkaline potassium permanganate or acidified potassium dichromate supplies the oxygen. The colour change is the observation: the purple of permanganate disappears as long as there is alcohol left to oxidise, and the moment it stops disappearing the alcohol is used up. That is why these reagents are called oxidising agents and why the colour is the signal.
Addition — an unsaturated compound takes on two more atoms and becomes saturated. A nickel or palladium catalyst is needed:
The double bond opens and one hydrogen attaches to each carbon. Addition is possible only because the compound was unsaturated, which is exactly what makes bromine water a test for unsaturation — the bromine adds across the double bond and its colour disappears.
Substitution — one atom of a saturated compound is replaced by another. Sunlight drives it:
One hydrogen has been swapped for one chlorine, and the displaced hydrogen leaves as hydrogen chloride. Nothing was added; something was exchanged.
The distinction that is examined most often.
- Addition happens to unsaturated compounds; the molecule gains atoms and nothing leaves
- Substitution happens to saturated compounds; the molecule swaps one atom for another and a second product leaves
Count the products. An addition gives one product; a substitution gives two. That single count identifies the reaction type without any other information, and it is the quickest way to answer a name the type of reaction question.
A boundary case worth naming. Chlorine can keep substituting: the can lose another hydrogen, and so on, so the reaction gives a mixture rather than a single product. That is why substitution reactions of alkanes are hard to control, and why the equation is usually written for the first step only.
Combustion — burning in oxygen to give carbon dioxide and water, releasing heat and light.
Check the second equation: carbon and ; hydrogen and ; oxygen on the left and on the right. Saturated hydrocarbons burn with a blue flame and unsaturated ones with a sooty yellow one, as the previous part explained.
Oxidation — adding oxygen without burning, using an oxidising agent. An alcohol becomes a carboxylic acid:
Alkaline potassium permanganate or acidified potassium dichromate supplies the oxygen. The colour change is the observation: the purple of permanganate disappears as long as there is alcohol left to oxidise, and the moment it stops disappearing the alcohol is used up. That is why these reagents are called oxidising agents and why the colour is the signal.
Addition — an unsaturated compound takes on two more atoms and becomes saturated. A nickel or palladium catalyst is needed:
The double bond opens and one hydrogen attaches to each carbon. Addition is possible only because the compound was unsaturated, which is exactly what makes bromine water a test for unsaturation — the bromine adds across the double bond and its colour disappears.
Substitution — one atom of a saturated compound is replaced by another. Sunlight drives it:
One hydrogen has been swapped for one chlorine, and the displaced hydrogen leaves as hydrogen chloride. Nothing was added; something was exchanged.
The distinction that is examined most often.
- Addition happens to unsaturated compounds; the molecule gains atoms and nothing leaves
- Substitution happens to saturated compounds; the molecule swaps one atom for another and a second product leaves
Count the products. An addition gives one product; a substitution gives two. That single count identifies the reaction type without any other information, and it is the quickest way to answer a name the type of reaction question.
A boundary case worth naming. Chlorine can keep substituting: the can lose another hydrogen, and so on, so the reaction gives a mixture rather than a single product. That is why substitution reactions of alkanes are hard to control, and why the equation is usually written for the first step only.
Exam tip
What layout keeps a nomenclature and reactions answer safe?
Write the structure beside the name, and the functional group beside the family. Nomenclature marks are all-or-nothing, so the checks matter more here than the writing.
- Count every carbon, including the one in or . Ethanoic acid has two carbons, not three
- **Drop the e before a vowel ending: ethanol, propanone, ethanoic acid. Keep it before a prefix: chloroethane
- Identify the carbonyl carbon's neighbours to separate an aldehyde from a ketone — a hydrogen means aldehyde, two carbons means ketone
- Quote the u difference when asked about a homologous series, and show one subtraction to prove it
- Say *same functional group, differ by * in the definition. Both halves are needed
- Name the catalyst and the condition: nickel for hydrogenation, sunlight for chlorination, alkaline potassium permanganate for oxidation
- Count the products to identify addition against substitution: one product against two
- Give the observation as well as the equation where there is one — the purple colour fading, the bromine water decolourising
The misconception to name. Homologues and isomers are not the same thing. Homologues share a functional group and differ by ; isomers share a molecular formula and differ in structure.** A question asking for the next homologue of ethanol wants propanol, while one asking for an isomer of ethanol wants dimethyl ether — and the two answers have nothing in common.
- Count every carbon, including the one in or . Ethanoic acid has two carbons, not three
- **Drop the e before a vowel ending: ethanol, propanone, ethanoic acid. Keep it before a prefix: chloroethane
- Identify the carbonyl carbon's neighbours to separate an aldehyde from a ketone — a hydrogen means aldehyde, two carbons means ketone
- Quote the u difference when asked about a homologous series, and show one subtraction to prove it
- Say *same functional group, differ by * in the definition. Both halves are needed
- Name the catalyst and the condition: nickel for hydrogenation, sunlight for chlorination, alkaline potassium permanganate for oxidation
- Count the products to identify addition against substitution: one product against two
- Give the observation as well as the equation where there is one — the purple colour fading, the bromine water decolourising
The misconception to name. Homologues and isomers are not the same thing. Homologues share a functional group and differ by ; isomers share a molecular formula and differ in structure.** A question asking for the next homologue of ethanol wants propanol, while one asking for an isomer of ethanol wants dimethyl ether — and the two answers have nothing in common.
Did you know
How is a liquid cooking oil turned into a solid ghee?
Vegetable oils are liquids and animal fats are solids, at the same room temperature. That difference is not about the size of the molecules — it is about the double bonds in them.
Vegetable oils are unsaturated: their long carbon chains carry double bonds, which put kinks in the chain. Kinked molecules cannot pack closely, so they slide past one another easily and the substance is a liquid. Fats are saturated: their chains are straight, so they stack neatly, hold together more strongly, and the substance is a solid.
So to turn an oil into a solid, remove the double bonds — and that is exactly an addition reaction from the previous section. Hydrogen is passed through the oil at a suitable temperature in the presence of a nickel catalyst, and it adds across each double bond:
The product is vanaspati, the hydrogenated vegetable ghee sold in tins, and the process is called hydrogenation. It is the same reaction that converts ethene to ethane, run on a much larger molecule.
And the textbook adds a health note. Unsaturated fats are the better ones to cook with, so oils made from vegetables are preferred over hydrogenated fats and over animal fats. Hydrogenation improves the texture and the keeping quality and removes the very feature that made the oil preferable, which is a genuine trade-off rather than a simple improvement.
The same chemistry explains a kitchen observation. Oil left open for a long time smells and tastes wrong — the rancidity of an earlier chapter — and it happens because oxygen attacks those same double bonds. A saturated fat resists it for longer, which is part of why hydrogenated products keep better.
One test ties it all together. Add a few drops of bromine water to a vegetable oil and the colour fades; add it to a hydrogenated fat and it does not. That is the unsaturation test of the last chapter, used on food, and it is the simplest way to show that the two substances differ in exactly the way this section claims.
Vegetable oils are unsaturated: their long carbon chains carry double bonds, which put kinks in the chain. Kinked molecules cannot pack closely, so they slide past one another easily and the substance is a liquid. Fats are saturated: their chains are straight, so they stack neatly, hold together more strongly, and the substance is a solid.
So to turn an oil into a solid, remove the double bonds — and that is exactly an addition reaction from the previous section. Hydrogen is passed through the oil at a suitable temperature in the presence of a nickel catalyst, and it adds across each double bond:
The product is vanaspati, the hydrogenated vegetable ghee sold in tins, and the process is called hydrogenation. It is the same reaction that converts ethene to ethane, run on a much larger molecule.
And the textbook adds a health note. Unsaturated fats are the better ones to cook with, so oils made from vegetables are preferred over hydrogenated fats and over animal fats. Hydrogenation improves the texture and the keeping quality and removes the very feature that made the oil preferable, which is a genuine trade-off rather than a simple improvement.
The same chemistry explains a kitchen observation. Oil left open for a long time smells and tastes wrong — the rancidity of an earlier chapter — and it happens because oxygen attacks those same double bonds. A saturated fat resists it for longer, which is part of why hydrogenated products keep better.
One test ties it all together. Add a few drops of bromine water to a vegetable oil and the colour fades; add it to a hydrogenated fat and it does not. That is the unsaturation test of the last chapter, used on food, and it is the simplest way to show that the two substances differ in exactly the way this section claims.
Exam relevance
How do functional groups feed into JEE and NEET Chemistry?
This is foundation work for the organic chemistry of Class 11 and 12, which is one of the largest scoring areas of both papers.
Where nomenclature leads. Class 11 Organic Chemistry: Some Basic Principles extends IUPAC naming to branched chains, multiple functional groups, rings and priority orders — and it assumes the stem-plus-ending system you learn here without re-teaching it. JEE Main asks for the IUPAC name of a drawn structure directly, and marks nothing for a nearly-right name.
Where functional groups lead. Each group becomes a chapter of its own: Alcohols, Phenols and Ethers, Aldehydes, Ketones and Carboxylic Acids, and Haloalkanes and Haloarenes in Class 12, all examined in JEE and NEET. The idea that reactions belong to the group and not to the chain is the organising principle of all of them, and it is why those chapters can be learned at all.
Where homologous series lead. The regular u difference reappears in mass spectrometry and in physical-property trends, and the general formulas are used to identify a compound from its molecular mass in numerical questions. A molecular mass ending in an even number with a known functional group often identifies the compound outright.
Where the four reaction types lead. Addition, substitution, oxidation and elimination become mechanisms in Class 11 and 12, with electrophiles, nucleophiles and free radicals. The sunlight-driven chlorination of methane you meet here is the standard example of a free-radical substitution there, and hydrogenation is the standard catalytic addition. The names do not change; only the explanation gets deeper.
Question types to expect. At this level: identify the group, name the compound, give the next homologue, name the reaction type. In competitive papers: IUPAC names of complicated structures, identify the product of a named reaction, and assertion-reason items on why a particular reagent is used.
The single trap that costs marks. Miscounting the carbons in an acid or an aldehyde. The functional group's own carbon belongs to the chain, so is ethanoic acid and not propanoic acid. In JEE this error names the wrong compound and loses the whole question.
A second trap. Confusing addition with substitution. Addition needs unsaturation and gives one product; substitution needs a saturated compound and gives two. Assertion-reason items are built on exactly this pairing.
Board versus competitive emphasis. The CBSE paper marks the group, the name, the equation and the condition; a competitive paper marks a name or a product. The transferable habit is naming the group first — once the group is identified, both the family and the likely reaction follow.
Where nomenclature leads. Class 11 Organic Chemistry: Some Basic Principles extends IUPAC naming to branched chains, multiple functional groups, rings and priority orders — and it assumes the stem-plus-ending system you learn here without re-teaching it. JEE Main asks for the IUPAC name of a drawn structure directly, and marks nothing for a nearly-right name.
Where functional groups lead. Each group becomes a chapter of its own: Alcohols, Phenols and Ethers, Aldehydes, Ketones and Carboxylic Acids, and Haloalkanes and Haloarenes in Class 12, all examined in JEE and NEET. The idea that reactions belong to the group and not to the chain is the organising principle of all of them, and it is why those chapters can be learned at all.
Where homologous series lead. The regular u difference reappears in mass spectrometry and in physical-property trends, and the general formulas are used to identify a compound from its molecular mass in numerical questions. A molecular mass ending in an even number with a known functional group often identifies the compound outright.
Where the four reaction types lead. Addition, substitution, oxidation and elimination become mechanisms in Class 11 and 12, with electrophiles, nucleophiles and free radicals. The sunlight-driven chlorination of methane you meet here is the standard example of a free-radical substitution there, and hydrogenation is the standard catalytic addition. The names do not change; only the explanation gets deeper.
Question types to expect. At this level: identify the group, name the compound, give the next homologue, name the reaction type. In competitive papers: IUPAC names of complicated structures, identify the product of a named reaction, and assertion-reason items on why a particular reagent is used.
The single trap that costs marks. Miscounting the carbons in an acid or an aldehyde. The functional group's own carbon belongs to the chain, so is ethanoic acid and not propanoic acid. In JEE this error names the wrong compound and loses the whole question.
A second trap. Confusing addition with substitution. Addition needs unsaturation and gives one product; substitution needs a saturated compound and gives two. Assertion-reason items are built on exactly this pairing.
Board versus competitive emphasis. The CBSE paper marks the group, the name, the equation and the condition; a competitive paper marks a name or a product. The transferable habit is naming the group first — once the group is identified, both the family and the likely reaction follow.
Key takeaways
What should you know about functional groups before ethanol and soap?
Five groups, one series rule, one naming system and four reaction types.
- The functional group carries the chemistry; the hydrocarbon chain is an inert framework
- The five groups: halogen (, ), alcohol (), aldehyde (), ketone () and carboxylic acid ()
- Aldehyde against ketone: the carbonyl carbon carries a hydrogen in an aldehyde and two carbons in a ketone
- A homologous series shares a functional group and differs by , so consecutive molecular masses differ by ** u
- Chemical properties stay similar along a series; physical properties drift — boiling points rise, water solubility falls
- IUPAC naming: stem from the carbon count, ending from the group — -ol, -al, -one, -oic acid — and halogens as prefixes
- Drop the final e before a vowel ending: ethanol, propanone, ethanoic acid
- Count the functional group's own carbon as part of the chain
- Combustion gives carbon dioxide and water; oxidation turns an alcohol into an acid with an oxidising agent; addition saturates an unsaturated compound over a nickel catalyst; substitution swaps an atom in a saturated compound
- Addition gives one product, substitution gives two — count them to identify the type
- Homologues differ by ; isomers share a formula** — the two are not interchangeable
The sharpest self-test is the naming pair. Write the structures of butanoic acid and butanal, count the carbons in each, and then name and from their formulas alone.
- The functional group carries the chemistry; the hydrocarbon chain is an inert framework
- The five groups: halogen (, ), alcohol (), aldehyde (), ketone () and carboxylic acid ()
- Aldehyde against ketone: the carbonyl carbon carries a hydrogen in an aldehyde and two carbons in a ketone
- A homologous series shares a functional group and differs by , so consecutive molecular masses differ by ** u
- Chemical properties stay similar along a series; physical properties drift — boiling points rise, water solubility falls
- IUPAC naming: stem from the carbon count, ending from the group — -ol, -al, -one, -oic acid — and halogens as prefixes
- Drop the final e before a vowel ending: ethanol, propanone, ethanoic acid
- Count the functional group's own carbon as part of the chain
- Combustion gives carbon dioxide and water; oxidation turns an alcohol into an acid with an oxidising agent; addition saturates an unsaturated compound over a nickel catalyst; substitution swaps an atom in a saturated compound
- Addition gives one product, substitution gives two — count them to identify the type
- Homologues differ by ; isomers share a formula** — the two are not interchangeable
The sharpest self-test is the naming pair. Write the structures of butanoic acid and butanal, count the carbons in each, and then name and from their formulas alone.