CHEMISTRY GLOSSARY

alkenes    →   alkeni

Alkenes are acyclic branched or unbranched hydrocarbons having one or more double carbon-carbon bonds in their molecules. In the systematic chemical nomenclature, alkene names end in the suffix -ene. The general formula is C_nH_(2n+2)-2x were x is the number of double bonds. Alkenes that have only one double bond form a homologous series: ethene (ethylene), CH₂=CH₂, propene, CH₃CH₂=CH₂, etc. Alkenes typically undergo addition reactions to the double bond.

aromatic compounds    →   aromatski ugljikovodici

Aromatic compounds are a major group of unsaturated cyclic hydrocarbons containing one or more rings, typified by benzene, which has a 6-carbon ring containing three double bonds. All the bonds in benzene (C₆H₆) are the same length intermediate between double and single C-C bonds. The properties arise because the electrons in the p-orbitals are delocalised over the ring, giving extra stabilization energy of 150 kJ/mol over the energy of Kekulé structure. Aromatic compounds are unsaturated compounds, yet they do not easily partake in addition reactions.

Historical use of the term implies a ring containing only carbon (e.g., benzene, naphthalene), but it is often generalized to include heterocyclic structures such as pyridine and thiophene.

benzene    →   benzen

Benzene is a colourless liquid hydrocarbon, C₆H₆, b.p. 80 °C. It is now made from petroleum by catalytic reforming (formerly obtained from coal tar). Benzene is the archetypal aromatic compound. It has an unsaturated molecule, yet will not readily undergo addition reactions. On the other hand, it does undergo substitution reactions in which hydrogen atoms are replaced by other atoms or groups.

In 1865, Friedrich August Kekulé purposed the benzene molecule structure as a hexagonal ring which consists of six carbon atoms with alternate carbon-carbon single and carbon-carbon double bond. But such a structure should be highly reactive, and so didn't account for the unreactive nature of benzene. We now know that the best representation for the structure of benzene is indeed, hexagonal, with each C-C bond distance being identical and intermediate between those for a single and double bond. The π-orbitals from each neighbouring carbon atom overlap to form a delocalised molecular orbital which extends around the ring, giving added stability and with it, decreased reactivity. That is the reason the structural formula of benzene represents as a hexagon with a circle in the center which represents the delocalized electrons.

dehydrogenation    →   dehidrogenacija

Dehydrogenation is a chemical reaction in which hydrogen is removed from a compound. Dehydrogenation of organic compounds converts single carbon-carbon bonds into double bonds. It is usually affected by means of a metal catalyst or in biological systems by enzyme dehydrogenases.

dienes    →   dieni

Dienes are unsaturated organic compounds that contain two fixed double bonds between carbon atoms. Dienes in which the two double-bond units are linked by one single bond are termed conjugated.

olefin    →   olefin

Olefins are acyclic and cyclic hydrocarbons having one or more carbon-carbon double bonds, apart from the formal ones in aromatic compounds. The class olefins subsume alkenes and cycloalkenes and the corresponding polyenes.

fat    →   mast

Fats are esters of glycerol and long chain carboxylic acids. Fats occur widely in plants and animals as a means of storing food energy, having twice the calorific value of carbohydrates. Fats derived from plants and fish generally have a greater proportion of unsaturated fatty acids than those from mammals. Fats may be either solid or liquid at room temperature, depending on their structure and composition. Unsaturated fats are liquid at room temperature.

Plant oils may be hardened by the addition of hydrogen atoms, converting double bonds to single bonds. This process is known as hydrogenation. Hydrogenated vegetable oils are often present in margarine and other processed foods.

Alkali hydrolysis of fat with sodium hydroxide it gives glycerol and soap (i.e. a mixture of the sodium salts of the fatty acids).

unsaturated hydrocarbon    →   nezasićeni ugljikovodik

Unsaturated hydrocarbons are organic compounds containing double (alkenes) or triple (alkynes) bonds in their molecules.

omega-3 fatty acids    →   omega-3 masne kiseline

Omega-3 fatty acids are polyunsaturated fatty acids, meaning they contain more than one double bond. The name omega-3 indicates that the first double bond occurs on the third carbon atom (n-3) from the methyl (-CH₃) end of the molecule (omega position). The three main omega-3 fatty acids are alpha-linolenic acid (ALA, 18:3n-3), eicosapentaenoic acid (EPA, 20:5n-3), and docosahexaenoic acid (DHA, 22:6n-3). ALA comes from plants. EPA and DHA come from fish.

Similarly, the first double bond in omega-6 fatty acids is located between the sixth and seventh carbon atom (n-6) from the methyl end of the fatty acid (omega end).

saturated fatty acid    →   zasićena masna kiselina

Saturated fatty acid is a fatty acid carrying the maximum possible number of hydrogen atoms (It doesn’t have any double bounds in the alkyl chain). The most important of these are: