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Diaphragm (optics)
A diaphragm, or iris diaphragm, is an adjustable opening in an optical system, typically of overlapping metal leaves, that controls how much light passes through.
Diapycnal mixing
Diapycnal mixing is the turbulent transport of heat, salt, and tracers across density surfaces in stratified fluids, driven mainly by breaking internal waves and supplying the energy the ocean's overturning circulation needs.
Diary study
A diary study is a qualitative, quantitative, or mixed research method in which participants record experiences and behaviors in daily life over days to months, reducing retrospection bias.
Diaspore
Diaspore is an aluminum oxide hydroxide mineral, a principal aluminum-bearing component of bauxite alongside gibbsite and böhmite, and a color-change gemstone sold as Zultanite or Csarite.
Diastereomer
Diastereomers, also called diastereoisomers, are stereoisomers that are not mirror images, unlike enantiomers, so they differ in melting point and can be separated by crystallization.
Diastereomeric excess
Diastereomeric excess (de, or diastereoisomer excess) is a stereochemistry measure: the difference between the mole fractions of two diastereomers, defined by IUPAC by analogy with enantiomeric excess.
Diastereoselectivity
Diastereoselectivity is the preferential formation in a chemical reaction of one diastereoisomer over another, quantified by diastereomeric ratio and rationalized by models such as Cram's rule and Felkin–Anh.
Diastereotopic
Diastereotopic describes two identical atoms or groups in a molecule whose separate replacement by another group yields diastereomers, stereoisomers that are not mirror images of each other.
Diatomaceous earth
Diatomaceous earth, also called diatomite or kieselguhr, is a soft, finely porous siliceous sedimentary rock made of fossilized diatom skeletons, used mainly as a filter aid and insecticide.
Diatomic molecule
A diatomic molecule is a molecule made of exactly two atoms, either of the same element, such as H2 and O2, or of different elements, such as CO.
Diavik Diamond Mine
The Diavik Diamond Mine was a Rio Tinto diamond mine on an island in Lac de Gras, Northwest Territories, Canada, producing over 150 million carats from 2003 to 2026.
Diazinon
Diazinon, also sold as Dimpylate or Basudin, is a synthetic organophosphate insecticide with formula C12H21N2O3PS, registered in 1956 and phased out of residential use by 2004 over health risks.
Diazomethane
Diazomethane (CH₂N₂) is the simplest diazo compound, a yellow gas that is highly toxic and explosive, so it is freshly prepared in dilute ether solution to methylate acids in the laboratory.
Diazonium compound
A diazonium compound, or diazonium salt, is a salt of the cation R-N2+, known since 1858 as a versatile intermediate in aromatic chemistry, though many are thermally unstable and hazardous.
Diazotization
Diazotization is the chemical conversion of a primary aromatic amine into an arenediazonium salt by nitrous acid at low temperature, introduced by Peter Griess in 1863 and central to azo dye production.
Diazoxide
Diazoxide is a benzothiadiazine-derived drug that opens ATP-sensitive potassium channels; originally an antihypertensive, it treats hypoglycemia from excess insulin and, as a choline salt, hyperphagia in Prader-Willi syndrome.
Dibenzo-18-crown-6
Dibenzo-18-crown-6 (DB18C6) is a cyclic polyether first discovered by Charles J. Pedersen at DuPont, and its subsequent work led to a 1987 Nobel Prize.
Dibenzodioxin
Dibenzodioxin, or dibenzo-p-dioxin, is a tricyclic aromatic compound, C12H8O2, in which two benzene rings are fused to a central 1,4-dioxin ring bridged by two oxygen atoms.
Dibenzothiophene
Dibenzothiophene (DBT) is an organosulfur compound with formula C12H8S, consisting of two benzene rings fused to a central thiophene ring; it occurs in crude oil and is the model compound for desulfurization-resistant sulfur in fuels.
Dibenzoylmethane
Dibenzoylmethane is a beta-diketone, acetylacetone with both methyl groups replaced by phenyl groups, whose derivative avobenzone is among the most common UVA filters in sunscreens.
Dibenzylideneacetone
Dibenzylideneacetone, also called dibenzalacetone, is a bright-yellow organic compound with formula C17H14O, made from benzaldehyde and acetone and used in sunscreens and palladium catalysts such as Pd2(dba)3.
Diberyllocene
Diberyllocene (CpBeBeCp) is an organometallic beryllium compound with a direct beryllium–beryllium bond, first synthesized by Boronski and Aldridge at Oxford in 2023 and published in Science.
Diborane
Diborane (B₂H₆), also called boroethane, is the simplest stable boron hydride, a colorless, highly toxic, extremely flammable gas used to dope silicon in semiconductor manufacturing.
Diborene
A diborene is a compound containing a boron–boron double bond, the heavier group 13 analog of an alkene; the first neutral example was reported in 2007.
Diboryne
A diboryne is a neutral compound of the form L→B≡B←L, with a boron-boron triple bond; the first stable example, B₂(IDipp)₂, was isolated in 2012.
Dibromsalan
Dibromsalan (4',5-dibromosalicylanilide, DBS, temasept I) is a brominated salicylanilide disinfectant formerly used in soaps, cosmetics, and veterinary flukicide mixtures, withdrawn after causing photoallergic dermatitis.
Dibucaine
Dibucaine, also known as cinchocaine, is a potent amino amide local anesthetic developed in 1925, used mainly in topical ointments for hemorrhoids and minor skin irritation.
Dibutyl phthalate
Dibutyl phthalate (DBP) is a manufactured phthalate ester, a colorless oily liquid used chiefly as a plasticizer in plastics, paints, and adhesives, and formerly in nail polish.
Dicalcium phosphate
Dicalcium phosphate, or dibasic calcium phosphate, is the calcium phosphate salt CaHPO4, used as the food additive E 341 (ii), a feed phosphate, and a bone-repair ceramic.
Dicalcium silicate
Dicalcium silicate (Ca₂SiO₄), known as belite in cement, is the second main silicate phase of Portland cement clinker, making up 15 to 30% and hydrating more slowly than alite.