11.2 Naming organic compounds
- Syllabus
- 0620–2026–2027
- Topic
- 11.2
- Level
- —
Learning objectives
11.2.1Displayed formulae of: (a) methane and• Name and draw the displayed formulae of: (a) methane and ethane (b) ethene (c) ethanol (d) ethanoic acid (e) the products of the reactions stated in sections 11.4–11.711.2.2Type of compound present, given a• State the type of compound present, given a chemical name ending in -ane, -ene, -ol, or -oic acid or from a molecular formula or displayed formula11.2.3Structural and displayed formulae of• Name/draw structural and displayed formulae of unbranched alkanes, alkenes (including but-1-ene/but-2-ene), alcohols (propan-1-ol/propan-2-ol/butan-1-ol/butan-2-ol) and carboxylic acids up to four carbons11.2.4Displayed formulae of the unbranched• Name and draw the displayed formulae of the unbranched esters which can be made from unbranched alcohols and carboxylic acids, each containing up to four carbon atoms
Name and draw the five foundational molecules
| Name | Structural formula | Feature to preserve |
|---|---|---|
| methane | CH₄ | one carbon with four C–H bonds |
| ethane | CH₃CH₃ | one C–C single bond |
| ethene | CH₂=CH₂ | one C=C double bond |
| ethanol | CH₃CH₂OH | terminal –OH group |
| ethanoic acid | CH₃COOH | terminal –COOH group |
Displayed formulae:
Methane Ethane Ethene
H H H H H
| | | | |
H—C—H H—C—C—H C=C
| | | | |
H H H H H
Ethanol: Ethanoic acid:
H H H O
| | | ||
H—C—C—O—H H—C—C—O—H
| | |
H H H
For a named reaction product from sections 11.4–11.7, first identify its homologous series and carbon count, then draw every atom and bond with valid valencies.
Do not omit the O–H bond in ethanol or ethanoic acid. In ethanoic acid, one oxygen is double-bonded to carbon and the other is bonded to both carbon and hydrogen.
Classify an organic compound from its name or formula
| Name ending | Compound type | Formula clue |
|---|---|---|
| -ane | alkane | only C–C single bonds; CₙH₂ₙ₊₂ |
| -ene | alkene | contains C=C; CₙH₂ₙ |
| -ol | alcohol | contains –OH |
| -oic acid | carboxylic acid | contains –COOH |
From a name, use the suffix. From a displayed or structural formula, locate the functional group or C=C bond. From a molecular formula, compare it with the relevant general formula and any stated structural information.
Propanoic acid ends in -oic acid and contains the –COOH group, so it is a carboxylic acid. Ethene ends in -ene and contains C=C, so it is an alkene.
A molecular formula can sometimes fit more than one possible structure, so use the displayed formula or functional-group evidence whenever it is supplied.
Name and draw unbranched compounds up to four carbons
| Carbon atoms | Prefix | Alkane example |
|---|---|---|
| 1 | meth- | methane |
| 2 | eth- | ethane |
| 3 | prop- | propane |
| 4 | but- | butane |
| Family | Naming rule | Required examples |
|---|---|---|
| alkane | prefix + -ane | methane to butane |
| alkene | prefix + double-bond position + -ene | ethene, propene, but-1-ene, but-2-ene |
| alcohol | prefix + –OH position + -ol | propan-1-ol, propan-2-ol, butan-1-ol, butan-2-ol |
| carboxylic acid | prefix + -oic acid | methanoic to butanoic acid |
Choose the longest unbranched carbon chain, number it from the end that gives C=C or –OH the lowest position, then add the correct suffix. Draw the structural formula first and expand it to a displayed formula when every atom and bond is required.
But-1-ene is CH₂=CHCH₂CH₃; but-2-ene is CH₃CH=CHCH₃. Propan-1-ol is CH₃CH₂CH₂OH; propan-2-ol is CH₃CH(OH)CH₃.
The carbon of the –COOH group is part of the main chain. Position numbers are needed when the –OH group or C=C bond can occur in more than one position.
Name and draw unbranched esters
An ester contains the linkage –COO– and is formed from a carboxylic acid and an alcohol.
| Source | Part of ester name | Example |
|---|---|---|
| alcohol | first word ending in -yl | ethanol → ethyl |
| carboxylic acid | second word ending in -oate | propanoic acid → propanoate |
Name the alcohol-derived alkyl group first, then the acid-derived alkanoate group. To draw the ester, place the acid carbonyl next to –O– and attach the alcohol-derived carbon chain after that oxygen.
| Alcohol + acid | Ester name | Structural formula |
|---|---|---|
| methanol + ethanoic acid | methyl ethanoate | CH₃COOCH₃ |
| ethanol + methanoic acid | ethyl methanoate | HCOOCH₂CH₃ |
| propan-1-ol + ethanoic acid | propyl ethanoate | CH₃COOCH₂CH₂CH₃ |
| ethanol + butanoic acid | ethyl butanoate | CH₃CH₂CH₂COOCH₂CH₃ |
Within this objective, use unbranched alcohols and unbranched carboxylic acids containing no more than four carbon atoms each.
Do not reverse the name: the alcohol supplies the first -yl part and the acid supplies the second -oate part. The ester linkage is –C(=O)–O–, not –C–O–C(=O)– with the source labels swapped.