| ring 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) |
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| ring enhancement | In computed tomography, when a bright circle appears on an image made after injection of contrast medium, characteristic of localization of the contrast in the wall of an abscess. (05 Mar 2000) |
| ring finger | Fourth finger. Synonym: digitus annularis, fourth finger. (05 Mar 2000) |
| ring-knife | A circular or oval ring with internal cutting edge, on the model of the carpenter's spoke-shave, for shaving off tumours in the nasal and other cavities. Synonym: spoke-shave. (05 Mar 2000) |
| ring lesions in brain | <radiology> Hypodense, peripherally enhancing lesions, ** mnemonic: MAGIC DR., metastasis, abscess, glioma, granuloma, infarct, contusion, demyelination, resolving haematoma (12 Dec 1998) |
| ring ligament | Fibres of the articular capsule of the hip joint encircling the neck of the femur. Synonym: orbicular zone, ring ligament, zonular band. (05 Mar 2000) |
| ring-like corneal dystrophy | Thread-like opacities of the anterior corneal stroma, with acute, painful onset followed by decreased vision; autosomal dominant inheritance. (05 Mar 2000) |
| ring-necked | <zoology> Having a well defined ring of colour around the neck. <zoology> Ring-necked duck, an American scaup duck (Aythya collaris). The head, neck, and breast of the adult male are black, and a narrow, but conspicuous, red ring encircles the neck. This ring is absent in the female. Synonym: ring-neck, ring-necked blackhead, ringbill, tufted duck, and black jack. Source: Websters Dictionary (01 Mar 1998) |
| ring of iris | Either of two zones on the anterior surface of the iris, separated by a circular line concentric with the pupillary border. Synonym: annulus iridis. (05 Mar 2000) |
| ring of Soemmerring | A mass of lenticular fibres enclosed between the anterior and posterior portion of the lenticular capsule, leaving the pupillary area relatively free. (05 Mar 2000) |
| ring pessary | A ring of rubber, plastic, or metal in which the cervix rests; designed to support the uterus and to correct prolapse of that organ. (05 Mar 2000) |
| ring precipitin test | A precipitin test in which antigen solution is carefully layered over antibody solution in a tube; as diffusion proceeds, a disk of precipitate forms where the antibody ratio is optimal. Synonym: ring test. (05 Mar 2000) |
| ring scotoma | An annular area of blindness in the visual field surrounding the fixation point in pigmentary degeneration of the retina and in glaucoma. (05 Mar 2000) |
| ring syringe | A type of Luer-Lok syringe with thumb and finger rings attached to the proximal end of the barrel and to the tip of the plunger, allowing operation of the syringe with one hand. Synonym: ring syringe. (05 Mar 2000) |
| ring-tailed | <zoology> Having the tail crossed by conspicuous bands of colour. <zoology> Ring-tailed cat, a young golden eagle. Source: Websters Dictionary (01 Mar 1998) |