| 'Greek letter alpha' | angular acceleration; first [carbon atom next to the carbon atom bearing the active group in organic... |
|---|---|
| at | air tight; atom, atomic |
| FAB | fast atom bombardment; formalin ammonium bromide; fragment, antigen-binding [of immunoglobulins]; Fr... |
| Ma | mass of atom |
| FAB | Fast Atom Bombardment |
|---|---|
| FAB-MS | Fast Atom Bombardment Mass Spectrometry |
| FAB MS | Fast Atom Bombardment Mass Spectroscopy |
| HA | heterocyclic amine |
| HCA | heterocyclic amine |
| acids, heterocyclic | A class of acids containing a ring structure in which atleast one atom other than carbon is incorporated. (12 Dec 1998) |
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| bicyclo compounds, heterocyclic | A class of saturated compounds consisting of two rings only, having two or more atoms in common, containing at least one hetero atom, and that take the name of an open chain hydrocarbon containing the same total number of atoms. (12 Dec 1998) |
| heterocyclic compound | Any compound in which the constituent atoms, or any part of them, form a ring. Used mainly in organic chemistry where: 1) numerous compound's contain rings of carbon atoms (carbocyclic compound's) or carbon atoms plus one or more atoms of other types (heterocyclic compound's), usually nitrogen, oxygen, or sulfur; 2) where the atoms in the ring are all of the same element (homocyclic or isocyclic compound); 3) where the ring is saturated or contains nonconjugated double bonds (alicyclic compound), the compound is similar in properties to the corresponding acyclic compound (e.g., cyclohexane resembles hexane); 4) where the ring contains conjugated double bonds in a closed loop in which there are 4n + 2 (where n is an integer) delocalised π electrons (Huckel's rule) (aromatic compound; e.g., benzene, pyridine), it is more stable than the corresponding saturated ring and exhibits unusual chemical properties characteristic of itself and not of other types of rings or of acyclic compound's. These aromatic compounds have the ability to sustain an induced ring current. Synonym: closed chain compound, ring compound. (05 Mar 2000) |
| heterocyclic compounds | Ring compounds having atoms other than carbon in their nuclei. (12 Dec 1998) |
| heterocyclic compounds, 1-ring | A class of organic compounds containing a ring structure made up of more than one kind of atom, usually carbon plus another atom. The ring structure can be aromatic or nonaromatic. (12 Dec 1998) |
| heterocyclic compounds, 2-ring | A class of organic compounds containing two ring structures, one of which is made up of more than one kind of atom, usually carbon plus another atom. The heterocycle may be either aromatic or nonaromatic. (12 Dec 1998) |
| heterocyclic compounds, 3-ring | A class of organic compounds containing three ring structures, one of which is made up of more than one kind of atom, usually carbon plus another atom. The heterocycle may be either aromatic or nonaromatic (12 Dec 1998) |
| heterocyclic compounds, bridged-ring | A class of organic compounds which contain two rings that share a pair of bridgehead carbon atoms. (12 Dec 1998) |
| heterocyclic compounds with 4 or more rings | A class of organic compounds containing four or more ring structures, one of which is made up of more than one kind of atom, usually carbon plus another atom. The heterocycle may be either aromatic or nonaromatic. (12 Dec 1998) |
| heterocyclic oxides | Oxides of a ring compound having atoms other than carbon in its ring. (12 Dec 1998) |
| steroids, heterocyclic | Steroidal compounds in which one or more carbon atoms in the steroid ring system have been substituted with non-carbon atoms. (12 Dec 1998) |
| activated atom | An atom possessing more than normal energy as a result of input of energy. See: excited state. Synonym: excited atom. (05 Mar 2000) |
| atom | <chemistry, physics, radiobiology> A particle of matter indivisible by chemical means. It is the fundamental building block of the chemical elements. The elements, such as iron, lead and sulphur, differ from each other because they contain different kinds of atoms. There are about six sextillion (6 followed by 21 zeros or 6 x 1021) atoms in an ordinary drop of water. According to present day theory, an atom contains a dense inner core (the nucleus) and a much less dense outer domain consisting of electrons in motion around the nucleus. Atoms are electrically neutral. (16 Dec 1997) |
| Bohr's atom | A concept or model of the atom in which the negatively charged electrons move in circular or elliptical orbits around the positively charged nucleus, energy being emitted or absorbed when electrons change from one orbit to another. (05 Mar 2000) |
| radioactive atom | <chemistry, physics> An atom with an unstable nucleus, which emits particulate or electromagnetic radiation (radioactive emission) to achieve greater stability. See: radionuclide, half-life, Becquerel. (05 Mar 2000) |
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