Homologous seriesA group of compounds in which there is a constant increment of change in molecular structure from one compound in the series to the next.The alkanes differ by one CH2 group each timeCnH2n+2
Types of formulasMolecular formula – C4H10Complete structural formulaCondensed structural formula – C – H bonds are understood.Condensed structural formula – C-H and C-C bonds understoodCarbon skeleton; hydrogens understood
Draw a complete structural formula for thestraight-chained alkane having 3 carbons
Branched-chain AlkanesSubstituent – an atom or group of atoms that can take the place of a hydrogen atom on a parent hydrocarbon molecule.Parent chain – the longest carbon chain. May not always be written in a straight line on paper.
Alkyl group – a hydrocarbon substituentCH3 – methylCH3CH2 – ethylCH3CH2CH2 – propylAlkyl group = alkane – 1 HName = -ane + ylWhat would CH3CH2CH2 CH2be called?
Branched-chain alkaneAn alkane with one or more alkyl groups attached.
Naming a branched-chain alkane1. Find the longest chain of carbons. This is the parent chain2. # the carbons on the parent chain. Starting with the end that will give the substituents the smallest numbers3. Add #s to the names of the substituent groups to identify their positions on the chain.
4. Use prefixes to indicate if a group appears more than once. Di – 2 Tri – 3 Tetra – 4 Penta – 5 5. List the names of the alkyl substituents in alphabetical order (ignore prefixes when alphabetizing.) 6. Use proper punctuation Commas separate #s from #s Hyphens separate #s from words
Properties of alkanesNonpolar – electrons are shared about equallyVery weak van der Walls forces (dispersion)Have a low mass, low boiling pointDo not dissolve in water.Flammable