C4H10 could be a straight chain or a branched one. Rearranging the same atoms changes the boiling point, and sometimes the whole family of compounds a molecule belongs to.
Structural isomers have the same molecular formula but a different structural formula. Chain isomers differ in the carbon skeleton (butane and methylpropane). Positional isomers have the same functional group in a different position (propan-1-ol and propan-2-ol). Functional group isomers belong to different homologous series (propanal and propanone; ethanoic acid and methyl methanoate). Branching lowers boiling point because branched molecules have less surface contact.
Generate every isomer of a formula in the simulator, then sort them into chain, positional and functional group isomers.
| Formula | Isomers | Number | Type |
|---|---|---|---|
| C4H10 | butane, methylpropane | 2 | chain |
| C5H12 | pentane, 2-methylbutane, 2,2-dimethylpropane | 3 | chain |
| C4H9Br | 1-bromobutane, 2-bromobutane, 1-bromo-2-methylpropane, 2-bromo-2-methylpropane | 4 | chain and positional |
| C3H8O | propan-1-ol, propan-2-ol, methoxyethane | 3 | positional and functional group |
| C3H6O | propanal, propanone (and others) | functional group | |
| C2H4O2 | ethanoic acid, methyl methanoate | functional group |
Drawing the same molecule twice is the commonest error: a chain drawn bent, or numbered from the other end, is not a new isomer. Name each structure; if two names are identical, the structures are the same. 3-bromobutane is not a new isomer; it is 2-bromobutane.
Four quick checks. Each correct answer earns XP and records this skill on your profile.
Structural isomers have:
How many structural isomers does C5H12 have?
Propan-1-ol and propan-2-ol are:
Propanal and propanone are:
Unlocks once the four checks above are done. Worth more XP, written to AS Paper 1 and Paper 2 standard.
How many structural isomers have the formula C4H9Br?
Which compound is a functional group isomer of ethanoic acid?
Why does 2,2-dimethylpropane have a lower boiling point than pentane?
Which pair are NOT structural isomers?
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