Emphatically Aliphatic! Trivia Quiz

Answer:

Organic chemistry is an extensive - and often complex - field of scientific enquiry that is centred on elemental carbon (C) and the compounds that feature it in their molecular makeup. One of the many groups of compounds that are of interest in organic chemistry are the hydrocarbons, which are - broadly speaking - chains consisting of carbon and hydrogen.

Hydrocarbons can be categorised as aliphatic (straight chains, branched chains and non-aromatic rings) or aromatic (typically containing a stable benzene-like ring that harbours a cloud of delocalised electrons) and together they are used - to varying extents - in the petrochemical industry for a wide range of purposes including the creation of plastics, paint, flavourings, fuels or cosmetics.

Aliphatic compounds can be categorised yet further with three of the most well known examples being the alkanes, alkenes and alkynes. Whilst sharing similar names, the three groups exhibit different chemical and physical behaviours that relate to the nature of the bonds between carbon atoms in the structure. The alkanes are formed exclusively of single carbon to carbon bonds (C-C) and are therefore considered to be saturated; alkenes have at least one double carbon to carbon bond (C=C) and alkynes present with at least one triple carbon-carbon bond.

Alkanes - including methane (CH4), ethane (C2H6), propane (C3H8), butane (C4H10) and Octane (C8H18) - have a chemical formula that follow the general expression CnH2n+2 with n representing the number of carbons in the structure.

The chemical formula for alkenes such as ethene (or ethylene, C2H4), propene (or propylene, C3H6) and nonene (C9H18) follow the general expression, CnH2n, where n must be greater than one. This means that the simplest alkene is ethene which has two carbons; were there to be just one carbon, then the structure would not have a double bond and would instead take the form of methane, an alkane.

The basic alkynes such as acetylene (or ethyne, C2H2) and ethylacetylene (or butyne, C4H6) follow the general formula, CnH2n-2, with the reduced ratio of carbon to hydrogen atoms reflecting the existence of a triple bond. Outside of welding and the acetylene torch, the alkynes constitute a fairly obscure and niche class of hydrocarbon compared to the alkanes and alkenes.

Aliphatic hydrocarbons are not always the relatively simple carbon chains that have thus far been described; compounds such as cyclohexene (a ring of six carbon atoms with exclusively single bonds) and limonene (a compound found in citrus peel that has an altogether more complex molecular structure) are aliphatic despite first impressions. Aliphatic limonene - one of the compounds responsible for the fresh, zingy smell of oranges, lemons and the like - is therefore a good example of the fact that in chemistry the term "aromatic" does not relate to smell. Indeed, there exist scented aliphatic hydrocarbons and odourless aromatic compounds. Definitions are everything!

With regard to the incorrect answers, benzene, phenol, toluene and naphthalene are all aromatic whilst bromine and barium are two elements that occupy a space on the periodic table.