Organic molecule explorer
Build homologous series member by member with their displayed formulae, names and boiling points, then find every isomer of a molecular formula, including cis–trans and optical isomers at A Level.
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Learning objectives
- describe a homologous series as a group of compounds with a general formula, similar chemical properties and showing a gradation in physical properties as a result of increase in the size and mass of the molecules, e.g. melting and boiling points; viscosity
- describe the alkanes as a homologous series of saturated hydrocarbons with the general formula CnH2n+2
- draw the structures of unbranched alkanes, C1 to C3, and name the unbranched alkanes methane to propane
- describe the alkenes as a homologous series of unsaturated hydrocarbons with the general formula CnH2n
- draw the structures of unbranched alkenes, C2 and C3, and name the unbranched alkenes ethene and propene
- describe the alcohols as a homologous series containing the –OH group
- draw the structures of unbranched alcohols, C1 to C3, and name the unbranched alcohols methanol to propanol
- describe the carboxylic acids as a homologous series containing the –CO2H group
- draw the structures of branched and unbranched alkanes, C1 to C4, and name the unbranched alkanes methane to butane
- define isomerism and identify isomers
- draw the structures of branched and unbranched alkenes, C2 to C4, and name the unbranched alkenes ethene to butene
- draw the structures of branched and unbranched alcohols, C1 to C4, and name the unbranched alcohols methanol to butanol
- draw the structures of carboxylic acids, C1 to C4, and name the unbranched acids methanoic acid to butanoic acid
- deduce the name and formula of an ester from the unbranched carboxylic acid, C1 to C4, and alcohol, C1 to C4, and vice versa.
- interpret, and use the nomenclature, general formulae and structural formulae (including displayed formulae) of the following classes of compounds: — hydrocarbons (alkanes, alkenes and benzene)
- interpret, and use the nomenclature, general formulae and structural formulae (including displayed formulae) of the following classes of compounds: — halogenoalkanes
- interpret, and use the nomenclature, general formulae and structural formulae (including displayed formulae) of the following classes of compounds: — alcohols (including primary, secondary and tertiary)
- interpret, and use the nomenclature, general formulae and structural formulae (including displayed formulae) of the following classes of compounds: — carboxylic acids
- interpret, and use the nomenclature, general formulae and structural formulae (including displayed formulae) of the following classes of compounds: — esters
- describe constitutional (structural) isomerism
- describe cis-trans isomerism in alkenes, and explain its origin in terms of restricted rotation due to the presence of π bonds [use of E, Z nomenclature is not required]
- deduce the possible isomers for an organic molecule of known molecular formula
- Representations and Nomenclature (A Level Organic)
- Isomerism and Stereochemistry (A Level Organic)
Propane, C₃H₈, structural formula CH₃CH₂CH₃. It boils at −42.1 °C.
- Molecular formula
- C3H8
- General formula
- CnH2n+2
- Boiling point
- −42.1 °C
- Isomers seen
- 0 of 3
- Stereoisomers
- none
Try this
0 of 4 doneStep through the alkanes from one carbon atom to six. (not done yet)
Each member adds one CH₂. The general formula CₙH₂ₙ₊₂ fits them all, and the boiling point rises as the molecules get bigger.
Compare an alcohol with the alkane that has the same number of carbon atoms. (not done yet)
Alcohol molecules attract each other more strongly, through hydrogen bonds between their –OH groups, so an alcohol boils far higher than the alkane of the same size.
Find all the isomers of C₅H₁₂. (not done yet)
Pentane, 2-methylbutane and 2,2-dimethylpropane share C₅H₁₂. More branching means less contact between molecules, so the boiling point falls: 36 °C, 28 °C, 10 °C.
Find all the alkene isomers of C₄H₈. (not done yet)
The double bond can move along the chain, or the chain can branch. At A Level, but-2-ene also has cis and trans forms, because the C=C bond cannot rotate. C₄H₈ also forms two rings, cyclobutane and methylcyclopropane, which are not alkenes.