All articles starting with a number or symbol
13,599 articles
4-8-4
The 4-8-4, popularly known as the Northern type, is a steam locomotive wheel arrangement with four leading, eight driving, and four trailing wheels, first built for the Northern Pacific Railway in 1926.
4-Aminobenzoic acid
4-Aminobenzoic acid, also known as para-aminobenzoic acid or PABA, is an aromatic organic compound with an amino group para to the carboxyl group, a folate precursor in bacteria.
4-Aminobiphenyl
4-Aminobiphenyl, also called 4-aminodiphenyl, is an aromatic amine and known human bladder carcinogen, classified by IARC as Group 1; US commercial production stopped in the mid-1950s.
4-Aminodiphenylamine
4-Aminodiphenylamine, also called N-phenyl-p-phenylenediamine or 4-ADPA, is an aromatic amine with formula C12H12N2, sold as Variamine Blue RT and used as the key intermediate for rubber antioxidants and antiozonants such as 6PPD.
4-Aminophenol
4-Aminophenol (para-aminophenol, p-aminophenol) is an aromatic amine and phenol whose amino group sits para to the hydroxyl group, used in photographic developers, dyes, and paracetamol manufacture.
4-Aminopyridine
4-Aminopyridine (4-AP), the drug fampridine or dalfampridine, blocks voltage-gated potassium channels and is approved to improve walking in multiple sclerosis; it also serves as a bird repellent.
4-Aminosalicylic Acid
4-Aminosalicylic acid, also called para-aminosalicylic acid or PAS, is a bacteriostatic antitubercular drug that entered clinical use in 1946 as the second exclusive tuberculosis drug after streptomycin.
4-Chlorophenol
4-Chlorophenol, also called p-chlorophenol or parachlorophenol, is a white crystalline solid with a chlorine atom at the para position, used chiefly as an intermediate in synthesizing dyes, fungicides, and drugs.
4-coumarate--CoA ligase
4-coumarate--CoA ligase (4CL, EC 6.2.1.12) is the plant branch-point enzyme converting hydroxycinnamic acids to hydroxycinnamoyl-CoA thioesters via ATP and AMP intermediates, feeding lignin and flavonoid biosynthesis through class I and class II gene-family isoforms.
4-Cyano-4'-pentylbiphenyl
4-Cyano-4'-pentylbiphenyl, almost always called 5CB, is a rod-shaped organic molecule, C₁₈H₁₉N, that forms a nematic phase between about 22 and 35 °C and was the first of the cyanobiphenyl liquid crystals.
4-Cyanopyridine
4-Cyanopyridine, also called isonicotinonitrile or pyridine-4-carbonitrile, is a white crystalline aromatic nitrile with a cyano group at the 4-position of a pyridine ring, used chiefly to make tuberculosis drugs like ethionamide and isoniazid.
4-Dimethylaminoazobenzene
4-Dimethylaminoazobenzene, also known as butter yellow, is a lipophilic azo dye once used to color butter and margarine, best known as a potent liver carcinogen in experimental animals.
4-Dimethylaminobenzaldehyde
4-Dimethylaminobenzaldehyde, also known as DMAB or p-DMAB, is an aromatic aldehyde best known as the active component of Ehrlich's reagent, used to detect indoles, pyrroles, porphobilinogen, and LSD.
4-Dimethylaminopyridine
4-Dimethylaminopyridine (DMAP), also called N,N-dimethylpyridin-4-amine, is an electron-rich pyridine derivative used as a nucleophilic acyl-transfer catalyst, best known as the catalyst of the Steglich esterification and for acylating sterically hindered alcohols.
4-Ethylphenol
4-Ethylphenol, also known as para-ethylphenol, is an organic compound used as a chemical intermediate and flavoring agent, known as the principal marker of Brettanomyces wine spoilage.
4-Fluoroamphetamine
4-Fluoroamphetamine, also called para-fluoroamphetamine, is a stimulant amphetamine derivative first synthesized in the 1940s, controlled under the 1971 UN convention and US schedule I since 2026.
4-H
4-H is the U.S. youth development program of the 109 land-grant universities and Cooperative Extension System, serving about six million youth. Founded from 1902 corn clubs, named for Head, Heart, Hands, and Health, funded by USDA NIFA.
4-HO-MET
4-HO-MET, also known as metocin or methylcybin, is a synthetic tryptamine psychedelic structurally related to psilocin and serotonin, first described in 1981 and sold online since the late 2000s.
4-hydroxybenzoate decarboxylase subunit C
4-hydroxybenzoate decarboxylase subunit C (ShdC, BsdC, VdcC) is the large catalytic subunit of bacterial UbiD-family, cofactor-independent, oxygen-sensitive reversible 4-hydroxybenzoate decarboxylases (EC 4.1.1.61), encoded in B-C-D gene clusters with subunit D required for activity.
4-Hydroxycoumarin
4-Hydroxycoumarin, also known as benzotetronic acid, is an organic compound with the formula C₉H₆O₃ and the structural nucleus of the vitamin K antagonist anticoagulants, including warfarin, acenocoumarol, and dicoumarol.
4-Hydroxynonenal
4-Hydroxynonenal (4-HNE) is a nine-carbon unsaturated aldehyde formed during peroxidation of n-6 polyunsaturated fatty acids; it forms protein adducts, acts as a signaling molecule, and is implicated in metabolic and neurodegenerative diseases and cancers.
4-Hydroxytamoxifen
4-Hydroxytamoxifen (4-OHT, afimoxifene) is a potent active metabolite of the breast cancer drug tamoxifen, identified in 1977, that binds the estrogen receptor as an antiestrogen and is studied as a topical gel.
4-Iodoanisole
4-Iodoanisole, also called p-iodoanisole or 1-iodo-4-methoxybenzene, is a white crystalline aryl iodide (C₇H₇IO) used as a reagent and building block in palladium-catalyzed cross-coupling chemistry and materials science.
4-manifold
A 4-manifold, or four-manifold, is a topological space locally homeomorphic to four-dimensional Euclidean space. Dimension 4 is the only one where Euclidean space admits exotic smooth structures.
4-Methyl-2-pentanol
4-Methyl-2-pentanol, also known as methyl isobutyl carbinol or MIBC, is a clear, colorless secondary alcohol produced alongside methyl isobutyl ketone and used mainly as a frother in mineral flotation.
4-Methylpyrazole
4-Methylpyrazole, known by the generic name fomepizole (trade name Antizol), is a drug that blocks alcohol dehydrogenase and is used as an antidote for methanol and ethylene glycol poisoning.
4-Methylumbelliferone
4-Methylumbelliferone, also known as hymecromone, is a coumarin derivative used as a fluorophore in enzyme assays and as the most studied inhibitor of hyaluronan synthesis.
4-Nitroaniline
4-Nitroaniline, also known as para-nitroaniline, is a yellow crystalline aromatic amine with a nitro group opposite the amino group on the benzene ring, used mainly as an intermediate in azo dyes, antioxidants, and pharmaceuticals.
4-Nitrophenol
4-Nitrophenol, also called p-nitrophenol, is a colorless to pale-yellow crystalline phenol derivative used to manufacture drugs such as acetaminophen, fungicides, insecticides, and dyes, and serving as a pH indicator.
4-Nitrophenyl phosphate
4-Nitrophenyl phosphate (pNPP) is an aryl phosphate ester, first reported in 1937, that serves as a chromogenic substrate for phosphatase assays in clinical diagnostics, ELISA, and enzyme research.