Physical world and mathematics

Hexabromocyclododecane

Hexabromocyclododecane (HBCD, also written HBCDD) is a brominated cycloaliphatic flame retardant used mainly in polystyrene building insulation, phased out globally as persistent, bioaccumulative, and toxic.

Hexachlorobenzene

Hexachlorobenzene, also called perchlorobenzene, is a fully chlorinated aromatic hydrocarbon, C6Cl6, once widely used as a fungicide before being banned from commercial production in most countries.

Hexachlorocyclohexane

Hexachlorocyclohexane (HCH) is an organochlorine insecticide, C6H6Cl6, existing as a mixture of eight stereoisomers; the gamma isomer is known as lindane, once a leading pesticide and now largely banned for agricultural use.

Hexachloroethane

Hexachloroethane, also called perchloroethane or HCE, is a colorless crystalline solid with a camphor-like odor, isolated by Michael Faraday in 1820 and used in military HC smoke.

Hexadecane

Hexadecane, also called n-cetane, is a straight-chain alkane with 16 carbon atoms, C₁₆H₃₄, a colorless liquid used as the cetane number 100 reference fuel for rating diesel ignition quality.

Hexadecimal

Hexadecimal, also known as base 16 or hex, is a numeral system using sixteen digits, 0–9 and A–F, serving in computing as a compact shorthand for binary.

Oct 21, 2026

Hexadecyl acetate

Hexadecyl acetate (cetyl acetate, palmityl acetate, CAS 629-70-9), a saturated C18 fatty ester used as a cosmetic emollient and EU-approved low-risk insect attractant pheromone, distinct from (Z)-11-hexadecenyl acetate.

Hexadecyltrimethylammonium bromide

Hexadecyltrimethylammonium bromide, better known as cetyltrimethylammonium bromide (CTAB) or cetrimonium bromide, is a quaternary ammonium salt and cationic surfactant used as a topical antiseptic, in DNA extraction, and in nanoparticle synthesis.

Hexadehydro Diels–Alder reaction

The hexadehydro-Diels–Alder (HDDA) reaction is a thermal cycloisomerization of a 1,3-diyne with an alkyne to form a benzyne, named and developed by Thomas R. Hoye and coworkers in 2012.

Hexafluoroacetone

Hexafluoroacetone, also known as perfluoroacetone, is the perfluorinated analog of acetone, a colorless, toxic, highly reactive gas first prepared in 1941 and used chiefly as an intermediate in polymer and monomer synthesis.

Hexafluoroethane

Hexafluoroethane, known as the refrigerant R-116, is a colorless, odorless, nonflammable perfluorocarbon gas in which all six hydrogen atoms of ethane are replaced by fluorine.

Hexafluorophosphate

Hexafluorophosphate is an octahedral anion, PF6, that coordinates weakly to cations and serves as a non-nucleophilic counterion; its lithium salt, LiPF6, dominates commercial lithium-ion battery electrolytes.

Hexafluoropropylene

Hexafluoropropylene (HFP), also called hexafluoropropene, is an odorless, colorless, noncombustible gas with the formula C₃F₆ used chiefly as a comonomer in FEP fluoropolymer production and to make hexafluoropropylene oxide.

Hexagon

A hexagon is a polygon with six straight sides and six angles, regular when all sides and angles are equal, with interior angles of 120°.

Hexagonal boron nitride encapsulation of graphene

Hexagonal boron nitride encapsulation of graphene is a device-fabrication technique that sandwiches graphene between insulating hBN flakes, enabling very high mobility and micron-scale ballistic transport.

Hexagonal boron nitride single-photon emitter

A hexagonal boron nitride single-photon emitter is an atomic-scale defect in the layered insulator h-BN that emits light one photon at a time at room temperature.

Hexagonal boron nitride spin defects

Hexagonal boron nitride spin defects are atom-like defects in hBN, chiefly the negatively charged boron vacancy, whose spins can be optically controlled at room temperature for quantum sensing.

Hexagonal close-packed

Hexagonal close-packed (HCP) is a crystal structure in which identical atoms stack in close-packed layers repeating ABABAB, giving each atom twelve equidistant nearest neighbors; it occurs in metals like magnesium, zinc, and titanium.

Hexagonal crystal family

The hexagonal crystal family, designated h, is one of six crystal families in three-dimensional crystallography, covering space groups with two free cell parameters, a and c.

Hexagram

A hexagram is a six-pointed star figure, most familiarly the compound of two equilateral triangles known as the Star of David and Seal of Solomon.

Hexamethonium

Hexamethonium is a ganglion-blocking bis-quaternary ammonium compound, introduced in 1952 as the first effective drug class for severe hypertension and now used only in research.

Hexamethylbenzene

Hexamethylbenzene, also known as mellitene, is an aromatic hydrocarbon in which all six hydrogen atoms of benzene are replaced by methyl groups; its X-ray structure proved the benzene ring is a flat hexagon.

Hexamethylbenzene dication

The hexamethylbenzene dication is a carbocation with one carbon bonded to six others in a pentagonal pyramid, first prepared in 1973 and confirmed by X-ray crystallography in 2016.

Hexamethyldisiloxane

Hexamethyldisiloxane (HMDSO) is the simplest linear methyl siloxane, a volatile liquid made from chlorotrimethylsilane and used as a silicone intermediate, plasma-deposition precursor, and cosmetic ingredient.

Hexamethylene diisocyanate

Hexamethylene diisocyanate (HDI), also called 1,6-diisocyanatohexane, is a colorless aliphatic diisocyanate used almost entirely to make polyurethane foams, coatings, and hardeners for two-component automobile paints.

Hexamethylenediamine

Hexamethylenediamine, also called 1,6-hexanediamine or diaminohexane, is a corrosive six-carbon diamine, made by hydrogenating adiponitrile, that is best known as the amine monomer of nylon 6,6.

Hexamethylenetetramine

Hexamethylenetetramine (C6H12N4), also known as hexamine or methenamine, is a cage-like white crystalline compound made from formaldehyde and ammonia, used to cure resins, make RDX, fuel tablets, and treat urinary infections.

Hexamethylphosphoramide

Hexamethylphosphoramide (HMPA), also called hexamethylphosphoric triamide, is a polar aprotic solvent used in organic synthesis to solvate metal cations and accelerate SN2 reactions, though its carcinogenicity limits its use.

Hexanal

Hexanal, also known as hexaldehyde or caproaldehyde, is a saturated fatty aldehyde, a clear colorless liquid with a pungent odor that becomes fruity on dilution.