CHEMISTRY GLOSSARY

glycoside    →   glikozid

Glycoside is one of a group of organic compounds in which a sugar group is bonded through its anomeric carbon to another group via a glycosidic bond. The sugar group is known as the glycon and the non-sugar group as the aglycon. According to the IUPAC definition, all disaccharides and polysaccharides are glycosides where the aglycone is another sugar.

In the free hemiacetal form, sugars will spontaneously equilibrate between the α and β anomers. However, once the glycosidic bond is formed, the anomeric configuration of the ring is locked as either α or β. Therefore, the alpha and beta glycosides are chemically distinct. They will have different chemical, physical, and biological properties. Many glycosides occur abundantly in plants, especially as flower and fruit pigments.

The term glycoside was later extended to cover not only compounds in which the anomeric hydroxy group is replaced by a group -OR, but also those in which the replacing group is -SR (thioglycosides), -SeR (selenoglycosides), -NR1R2 (N-glycosides), or even -CR1R2R3 (C-glycosides). Thioglycoside and selenoglycoside are legitimate generic terms; however the use of N-glycoside, although widespread in biochemical literature, is improper and not recommended here (glycosylamine is a perfectly acceptable term). C-Glycoside is even less acceptable. All other glycosides are hydrolysable; the C-C bond of C-glycosides is usually not. The use and propagation of names based on C-glycoside terminology is therefore strongly discouraged.

groups in periodic system of elements    →   skupine periodnog sustava

Periodic system of elements is divided into 18 groups of chemical elements. Elements belonging to the same group have a same number of valence electrons and similar chemical properties. Elements of main groups are in 1., 2., and in groups 13. to 18. Different groups of elements can be named according to the first element in the group (elements of boron group, elements of carbon group), or they have some special names (noble gases, halogenic elements, halyde elements, earthalkali and alkali metals).

haematite    →   hematit

Haematite is a mineral of iron(III) oxide Fe₂O₃. It is the most important ore of iron and usually occurs in two main forms: as a massive red kidney-shaped ore and as grey to black metallic crystals known as specular iron ore. Haematite is the major red colouring agent in rocks; the largest deposits are of sedimentary origin. In industry haematite is also used as a polishing agent (jeweller’s rouge) and in paints.

hafnium    →   hafnij

Hafnium was discovered by Dirk Coster (Denmark) and Georg Karl von Hevesy (Hungary) in 1923. The origin of the name comes from the Latin name Hafnia meaning Copenhagen. It is silvery, ductile metal. Exposed surfaces form oxide film. Resists alkalis and acids (except HF). Toxic. Metal ignites and burns readily. Hafnium is obtained from mineral zircon or baddeleyite. Used in reactor control rods because of its ability to absorb neutrons.

hassium    →   hassij

Hassium was discovered by Peter Armbruster, Gottfried Münzenber and their co-workers at the Heavy Ion Research Laboratory (Gesellschaft für Schwerionenforschung, GSI) in Darmstadt, Germany in 1984. The origin of the name is the Latin word Hassias meaning Hess, the German state. It is synthetic radioactive metal. Hassium was produced bythe bombardment of lead-208 with iron-58.

helium    →   helij

Helium was discovered by Pierre Jules César Janssen (France) and Sir William Ramsay (Scotland) in 1868. The origin of the name comes from the Greek word helios meaning sun. It is light, odourless, colourless inert gas. Second most abundant element in the universe. Helium is found in natural gas deposits from wells in Texas, Oklahoma and Kansas. Used in balloons, deep sea diving and welding. Also used in very low temperature research.

hemiacetal    →   poluacetal

Hemiacetals are organic compounds having the general formula R₂C(OH)OR’ (R’ ≠ H), derived from aldehydes or ketones by formal addition of an alcohol to the carbonyl group. Hemiacetals are generally unstable compounds. In some cases however, stable cyclic hemiacetals can be readily formed, especially when 5- and 6-membered rings are possible. In this case an intramolecular OH group reacts with the carbonyl group. Glucose and many other aldoses exist as cyclic hemiacetals whereas fructose and similar ketoses exist as cyclic hemiketals. Originally, the term was confined to derivatives of aldehydes (one R = H), but it now applies equally to derivatives of ketones (neither R = H).

high fructose corn syrup    →   visoko fruktozni kukuruzni sirup

High fructose corn syrup (HFCS) is commonly used in place of sugar in foods and drinks. Corn starch is hydrolyzed to glucose, which is then treated with glucose isomerase to produce a fructose-rich mixture. HFCS is available in a number of forms, named according to the percentage of fructose they contain, HFCS-55 for instance contains 55 % fructose and 45 % glucose. The enhanced sweetness, low cost and ease of use are the main reasons why manufacturers now prefer to use high fructose corn syrup instead of sugar.

Hirsch funnel    →   Hirschov lijevak

Hirsch funnels are essentially smaller Büchner funnels and primarily used to collect a desired solid from a relatively small volume of liquid (1-10 mL). The main difference is that the plate is much smaller, while the walls of the funnel angle outward instead of being vertical. It is named after the German chemist Robert Hirsch (1856-1913).

holmium    →   holmij

Holmium was discovered by Per Theodore Cleve (Sweden) in 1879. The origin of the name comes from the Greek word Holmia meaning Stockholm. It is fairly soft, malleable, lustrous, silvery metal. Reacts slowly with oxygen and water. Dissolves in acids. Can react violently with air or halogens. Holmium occurs in gadolinite. Most often from monazite sand. It has very few practical applications; however, it has some unusual magnetic properties that offer some hope for future applications.