CHEMISTRY GLOSSARY

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.

depression of freezing point    →   snižavanje ledišta

Depression of freezing point of a pure solvent is observed when substances are dissolved in it. The amount by which the freezing point is depressed is proportional to the number of molecules of solute and independent of their nature.

beta-glucan    →   beta-glukan

Beta-glucans are are naturally occurring polysaccharides that contain only glucose as structural components, and are linked with β-glycosidic bonds. They is the most known powerful immune stimulant. The most active forms of β-glucans are those comprising D-glucose units with β(1→3) links and with short side-chains of D-glucose attached at the β(1→6) position. These are referred to as beta-1,3/1,6 glucan. They are a major component of soluble dietary fiber, which can be found in cereal grains (oats, barley, wheat), yeast, and certain mushrooms (shiitake, maitake).

bidentate ligand    →   bidentatni ligand

Bidentate ligand is a ligand that has two "teeth" or atoms that coordinate directly to the central atom in a complex. An example of a bidentate ligand is ethylenediamine. A single molecule of ethylenediamine can form two bonds to a metal ion. The bonds form between the metal ion and the nitrogen atoms of ethylenediamine.

borane    →   borani

Borane is any of the group of compounds of boron and hydrogen (B₂H₆, B₄H₁₀, B₅H₉, B₅H₁₁...), many of which can be prepared by action of acid on magnesium boride (Mg₃B₂). Boranes are a remarkable group of compounds in that their structures cannot be described using the conventional two-electron covalent bond model.

catalyst    →   katalizator

Catalyst is a substance that increases the rate of a chemical reaction without itself undergoing any permanent chemical change. Catalysts that have the same phase as the reactants are homogenous catalysts (e.g. enzymes in biochemical reactions). Those that have a different phase are heterogeneous catalyst (e.g. metals or oxides used in gas reactions).

The catalyst provides an alternative pathway by which the reaction can proceed, in which the activation energy is lower. In thus increases the rate at which the reaction comes to an equilibrium, although it does not alter the position of the equilibrium.

diamagnetic    →   dijamagnetik

Diamagnetic materials are very weakly repelled by magnetic fields. The atoms or molecules of diamagnetic materials contain no unpaired spins.

disproportionation    →   disproporcioniranje

Disproportionation is a reaction in which the same molecule reduces and oxidates itself at the same time.

elementary reaction    →   elementarna reakcija

Elementary reaction is a reaction that occurs in a single step. Equations for elementary reactions show the actual molecules, atoms, and ions that react on a molecular level.

equivalent weight    →   ekvivalentna masa

Equivalent weight of a substance participating in a neutralization reaction is that mass of substance (molecule, ion, or paired ion) that either reacts with or supplies 1 mol of hydrogen ions in that reaction.

Equivalent weight of a substance participating in an oxidation/reduction reaction is that weight which directly or indirectly produces or consumes 1 mol of electrons.