Isomerism and its types
Substances with the same molecular formula but different structure and properties are isomers, and the phenomenon is isomerism; the term was introduced in the 1830s by J. Berzelius. In chain isomerism the carbon skeleton differs: C₄H₁₀ has n-butane and 2-methylpropane (isobutane), C₅H₁₂ has three isomers, hexane has 5 and heptane has 9. In position isomerism the functional group or double (triple) bond sits on different carbons: 1-chlorobutane and 2-chlorobutane, butene-1 and butene-2, propanol-1 and propanol-2. In interclass isomerism the formula is the same but the compounds belong to different classes: C₂H₆O fits both ethanol (alcohol) and dimethyl ether; C₃H₆O fits propanal (aldehyde) and propanone (ketone). Geometric isomerism arises because rotation about a double bond is impossible: if each double-bonded carbon carries two different substituents, the substituents can lie on the same side (cis-) or opposite sides (trans-).
Using two colours of plasticine balls and sticks, assemble all three isomers of C₅H₁₂ and sort them by the length of their longest chain. Work with sticks under adult supervision.