11.2Organic Chemistry
Naming organic compounds — Cambridge IGCSE Chemistry 0620 Revision Notes & Topical Questions
5 min read 10 parts Lesson 2 of 10 3 quizzes
Lesson summary
11.2 Naming organic compounds — Notes — IGCSE Chemistry notes: Name organic compounds from the number of carbon atoms and the functional group.Stem — shows the number of carbon atoms in the longest continuous chain.- End part — shows the functional group.CarbonsStem1meth2eth3prop…
- Carboxylic acids
- State the type of compound from a name ending in -ane, -ene, -ol or -oic acid, or from a molecular or displayed formula
- Count the carbons in the longest chain to find the stem
- Identify the functional group to find the ending
- Number the position of the group if needed
- Combine the stem and the ending
Section 1 of 10Parts of a name
Parts of a name
Stem
- Stem shows the number of carbon atoms in the longest continuous chain.
- End part
- - End part shows the functional group.
| Carbons | Stem |
|---|---|
| 1 | meth |
| 2 | eth |
| 3 | prop |
| 4 | but |
| 5 | pent |
| 6 | hex |
Section 2 of 10Endings and families
| Ending | Functional group | Family |
|---|---|---|
| -ane | C–C only | Alkane |
| -ene | C=C | Alkene |
| -anol | –OH | Alcohol |
| -anoic acid | –COOH | Carboxylic acid |
| -yl -anoate | –COO– | Ester |
| -amine | –NH2 | Amine |
- State the type of compound from a name ending in -ane, -ene, -ol or -oic acid, or from a molecular or displayed formula.
Section 3 of 10Naming method
1
Count the carbons in the longest chain to find the stem.
2
Identify the functional group to find the ending.
3
Number the position of the group if needed.
4
Combine the stem and the ending.
5
Check that the molecular formula fits the general formula of the series.
6
The -an- in alkane, alkanol and alkanoic acid names shows that the chain has only single C–C bonds.
Section 4 of 10Simple compounds to know
| Series | Functional group | 1 C | 2 C | 3 C | 4 C |
|---|---|---|---|---|---|
| Alkane | C–C | Methane | Ethane | Propane | Butane |
| Alkene | C=C | None | Ethene | Propene | Butene |
| Alcohol | –OH | Methanol | Ethanol | Propanol | Butanol |
| Carboxylic acid | –COOH | Methanoic acid | Ethanoic acid | Propanoic acid | Butanoic acid |
| Ester | –COO– | Methyl methanoate | Methyl ethanoate | Ethyl ethanoate | Ethyl propanoate |
Section 5 of 10Formulae of the simple compounds
Alkanes
- Alkanes methane CH4, ethane C2H6, propane C3H8, butane C4H10 and pentane C5H12.
Alkenes
- Alkenes ethene C2H4, propene C3H6 and butene C4H8.
- The smallest alkene is ethene, because two carbons are needed to form C=C.
Alcohols
- Alcohols methanol CH3OH, ethanol C2H5OH (CH3CH2OH) and propanol C3H7OH.
Carboxylic acids
- Carboxylic acids methanoic acid HCOOH, ethanoic acid CH3COOH, propanoic acid CH3CH2COOH and butanoic acid CH3CH2CH2COOH.
- (the acid in vinegar)
Esters
- Esters ethyl ethanoate is CH3COOC2H5.
The carbon of the –COOH group is counted in the chain, so CH3CH2COOH is propanoic acid.
Section 6 of 10Position numbers (Supplement)
Number the chain from the end that gives the functional group the lowest number.
Alkenes
- Alkenes ethene needs no number because it is the first alkene,
- but from butene onwards the number of the first double-bond carbon is stated, as in but-1-ene and but-2-ene.
Alcohols
- Alcohols after ethanol the carbon carrying –OH is stated, as in propan-1-ol, propan-2-ol, butan-1-ol and butan-2-ol.
Carboxylic acids
- Carboxylic acids no number is needed because the –COOH carbon is always carbon 1, and the carbon count includes it.
Alkenes
- Alkenes but-1-ene has the C=C on the first carbon and but-2-ene has it on the second carbon.
Alcohols
- Alcohols propan-1-ol, CH3CH2CH2OH, has –OH on the first carbon and propan-2-ol, CH3CH(OH)CH3, has it on the second carbon.
Numbering may start from the right so that the numbers in the name are as low as possible.
Section 7 of 10Naming esters (Supplement)
1
The alcohol part comes first, ending in -yl, and the acid part second, ending in -oate.
2
Methanol + propanoic acid gives methyl propanoate, and ethanol + ethanoic acid gives ethyl ethanoate + water.
3
In the displayed formula the C–O single-bond side is the alcohol part and the C=O side is the acid part,
- so the name is written backwards from the drawing.
4
Examples: methyl ethanoate, ethyl ethanoate and pentyl butanoate.
Section 8 of 10More from the specification
More from the specification
IUPAC Rules for the Longest Carbon Chain
- The root stem reflects the number of carbon atoms in the longest continuous chain: meth- (1), eth- (2), prop- (3), but- (4), pent- (5), hex- (6).
Suffixes for Characteristic Functional Groups
- The suffix designates the dominant functional group: -ane for alkanes, -ene for alkenes, -anol for alcohols, and -anoic acid for carboxylic acids.
Positional Isomerism in Alkenes and Alcohols
- Arabic numerals specify the location of the functional group along the carbon skeleton, numbering from the chain end that produces the lowest possible positional locator.
- (e.g. but-1-ene vs but-2-ene)
Structural isomers
- Compounds with the same molecular formula but different structural formulae.
Saturated
- Having only single carbon–carbon bonds.
Unsaturated
- Having at least one carbon–carbon double bond.
Hydrogen
- A gas that gives a squeaky pop with a lighted splint.
Property
- A feature that describes what a substance is like and what it does.
Homologous series
- A family of compounds with the same functional group and general formula.
Section 9 of 10Key terms
| Term | Meaning |
|---|---|
| Stem | the part of a name showing the number of carbons in the longest chain. |
| Functional group | the atom or group of atoms that decides the family and the name ending. |
| Alkane | a saturated hydrocarbon with a name ending in -ane. |
| Alkene | a hydrocarbon with a C=C bond and a name ending in -ene. |
| Alcohol | a compound containing –OH with a name ending in -ol. |
| Carboxylic acid | a compound containing –COOH with a name ending in -oic acid. |
| Ester | a compound containing –COO– named with -yl and -oate. |
Section 10 of 10Exam technique
1
Writing the ester name in the order of the drawing — the alcohol part (-yl) comes first, so it is ethyl ethanoate, not ethanoate ethyl
2
Adding a position number to ethene or to carboxylic acids — it is not needed
3
Counting a branch instead of the longest chain for the stem
4
Saying alcohols end in -ene, or confusing the –OH group with the hydroxide ion — alcohols end in -ol
5
Not numbering the –OH position after ethanol, or forgetting to count the –COOH carbon in the chain
Marked practiceQuizzes for this lesson
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