Chemical substance

An iron oxide, $\alpha \text{-}\mathrm{F}{\mathrm{e}}_2{\mathrm{O}}_3$. It typically has weaker induced magnetic susceptibility than magnetite but can preserve stable remanent magnetization.

An iron sulfide with composition often written ${\mathrm{Fe}}_{1-x}\mathrm{S}$. Its structure and composition determine whether it carries strong magnetization; not all varieties behave identically.

An iron oxide exhibiting ferrimagnetism, $\gamma \text{-}\mathrm{F}{\mathrm{e}}_2{\mathrm{O}}_3$, that can contribute to geological magnetic anomalies.

An organochlorine insecticide chemically distinct from DDD. Its use and unintended ecological effects were central to Silent Spring by Rachel Carson.

An organochlorine insecticide discussed in the Clear Lake case in Silent Spring by Rachel Carson. DDD is chemically distinct from DDT.

The chemical compound $\mathrm{HgO}$. Thermal decomposition can release oxygen and produce mercury; historical preparations of the red oxide featured in Joseph Priestley's and Antoine Lavoisier's investigations.

An aqueous solution of hydrogen fluoride. In silicon-processing mixtures it can dissolve oxidized silicon-containing surface material; its role should not be confused with an oxidant's role in creating that material.

$(\mathrm{iBu}{)}_2\mathrm{AlH}$, a hydride reducing reagent. Low-temperature, controlled-stoichiometry reduction can convert an ester into an aldehyde or a lactone into a lactol; conditions must prevent further reduction.

A neutral oxygen-donor extractant, $\mathrm{OP}(\mathrm{OBu}{)}_3$, often abbreviated TBP. It can solvate metal nitrate species in solvent extraction. Selectivity depends on acidity, metal oxidation state, diluent and subsequent stripping conditions.

A zinc salt used as a Lewis acid and coordination reagent.

A molecular titanium(IV) chloride used as a Lewis acid.

A hydride reagent that can coordinate nearby oxygen donors while reducing a carbonyl.

The ionic compound LiF, a discharge product of a lithium–carbon monofluoride battery.

An oxide semiconductor whose common wurtzite phase is piezoelectric.

A ferroelectric solid solution widely used for piezoelectric transduction.

A fused two-ring aromatic hydrocarbon.

A hydrogen-bonding unit capable of forming a strongly associated, self-complementary dimer through a four-hydrogen-bond array.

A macrocyclic scaffold constructed from phenolic rings and connecting methylene groups.

The silylating reagent $\mathrm{tBuM}{\mathrm{e}}_2\mathrm{SiCl}$, commonly abbreviated TBSCl. nucleophilic substitution at silicon converts an alcohol into a silyl ether.

A compound containing $\mathrm{R}-\mathrm{O}-\mathrm{O}-\mathrm{H}$. Its oxygen–oxygen bond distinguishes it from the corresponding alcohol.

The methylating reagent $\mathrm{FS}{\mathrm{O}}_2\mathrm{OMe}$. Nucleophilic attack at methyl displaces fluorosulfonate.

The oxonium salt $\mathrm{M}{\mathrm{e}}_3{\mathrm{O}}^{+}\mathrm{B}{\mathrm{F}}_4^{-}$, a strong methylating reagent. carbonyl O-methylation followed by alpha-deprotonation can form an enol ether.

The hydride reagent $\mathrm{NaB}{\mathrm{H}}_3\mathrm{CN}$. Its comparatively mild reactivity permits selected imine and iminium reductions.

The organotin hydride $\mathrm{B}{\mathrm{u}}_3\mathrm{SnH}$, a hydrogen-atom or hydride source depending on the reaction system.

An anionic species with a negatively charged carbon centre. Resonance stabilization and substituents control its basicity and nucleophilicity.

A molecule containing a large ring. Multiple inward-facing donor groups can preorganize it for metal-ion binding.

Ring formation favored by binding an anionic template that organizes the reactive precursors.

A positively charged three-membered nitrogen heterocycle. Intramolecular formation from a tertiary amino alcohol with an activated hydroxyl can be followed by regioselective nucleophilic ring opening and net ring expansion.

The chlorine oxyacid $\mathrm{HOCl}$. In polar heterogeneous chemistry it can react with hydrogen chloride to release molecular chlorine and water, helping convert reservoir chlorine into photolabile forms.

An imine N-oxide with a three-atom C–N–O dipolar electronic system.

A strong potassium amide base.

A strongly electrophilic silylating reagent.

A chlorosilane used to trap oxygen nucleophiles as trimethylsilyl ethers.

A strong lithium amide base used for enolate formation.

A compound containing two acyl groups joined through oxygen.

An acid anhydride whose two acyl groups belong to the same ring.

The five-membered cyclic anhydride of cis-butenedioic acid.

An organic compound bearing a covalently attached N3 group.

Tetramethylethylenediamine, a bidentate nitrogen-donor Ligand in coordination chemistry.

The six-pi-electron ion ${\mathrm{C}}_4{\mathrm{H}}_4^{2-}$. In an ideal equal-coupling four-site Hückel ring, one bonding and two nonbonding pi orbitals are filled, leaving the highest antibonding orbital empty.

A layered insulating boron–nitrogen material used as a substrate or encapsulation layer for two-dimensional materials. Assembly defects and exposed edges can compromise an otherwise effective cap.

A layered compound $\mathrm{Mo}{\mathrm{S}}_2$. Atomically thin films are used in electronic and optical devices; crystal phase, defects, thickness and the local environment affect their response.

A seven-carbon bicyclic framework with three paths between its bridgeheads containing two, two and one internal atoms. Mapping these paths is useful when checking a tandem Michael cyclization product.

The nitroalkane $\mathrm{C}{\mathrm{H}}_3\mathrm{N}{\mathrm{O}}_2$. Its nitronate can add to a carbonyl in a Henry reaction.

The nitroalkane $\mathrm{C}{\mathrm{H}}_3\mathrm{C}{\mathrm{H}}_2\mathrm{N}{\mathrm{O}}_2$. Alpha deprotonation gives a nitronate that can form carbon–carbon bonds.

The ionic compound $\mathrm{NaN}{\mathrm{H}}_2$, commonly used as a strong base. ketone deprotonation produces an enolate and ammonia.

A silicon–nitrogen material used as an insulating, protective and optical coating. Device films may be nonstoichiometric and hydrogenated; bulk $\mathrm{S}{\mathrm{i}}_3{\mathrm{N}}_4$ is not a complete description of every deposited film.

An oxygen-containing anion of boron. borates can contain trigonal $\mathrm{B}{\mathrm{O}}_3$ and tetrahedral $\mathrm{B}{\mathrm{O}}_4$ units joined by bridging oxygen.

The low-temperature crystalline phase of barium borate, used as a nonlinear optical crystal. A properly phase-matched and compensated source can use it for spontaneous parametric down-conversion; the choice of collected modes and compensation determines the resulting polarization entanglement.

The anion $[{\mathrm{B}}_3{\mathrm{O}}_6{]}^{3-}$ formed from three trigonal $\mathrm{B}{\mathrm{O}}_3$ units sharing corners in an alternating six-membered B–O ring. Each boron also has one terminal oxygen.

The anion $\mathrm{SC}{\mathrm{N}}^{-}$, which can coordinate through nitrogen or sulfur. Linkage changes donor identity without changing its formal charge.

thiocyanate can coordinate through nitrogen, sulfur, or both ends, and can bridge several metal centres. A linkage label specifies donor atoms, whereas the bridging index ${\mu }_n$ specifies the number of connected metals. A short C–N bond and long C–S bond favour an $\mathrm{N}\equiv \mathrm{C}-{\mathrm{S}}^{-}$ description; greater C–S and smaller C–N bond orders give more ${}^{-}\mathrm{N}=\mathrm{C}=\mathrm{S}$ character. Internal distances alone need not determine how many metals are attached.

A ${\mu }_3$ thiocyanate connecting three metal centres. In layered first-row divalent metal thiocyanates, its nitrogen coordinates one metal and its sulfur coordinates two others, giving an $\mathrm{M}{\mathrm{N}}_2{\mathrm{S}}_4$ octahedral coordination environment.

The dianion of pyridine-2,5-dicarboxylic acid, useful as a bridging ligand because its N,O donor pair and its more remote carboxylate can bind different metal centres.

Two phenyl rings joined directly by a carbon–carbon bond. Restricted rotation and appropriate substituents can produce axial chirality.

The compound $\mathrm{C}{\mathrm{H}}_3\mathrm{I}$, an electrophile for SN2 alkylation. The carbon is attacked as iodide leaves.

The compound $\mathrm{C}{\mathrm{H}}_2=\mathrm{CHC}{\mathrm{H}}_2\mathrm{Br}$. nucleophilic substitution at its bromomethylene carbon introduces an allyl group without consuming the alkene.

The diatomic molecule containing one hydrogen atom and one iodine atom. Its measured spectroscopic wavenumbers include anharmonic corrections beyond the two-term Morse oscillator model.^[ref]

The gaseous hydrogen halide consisting of one hydrogen atom and one bromine atom. Its molecular vibration can be studied through its vibrational fundamental and weak vibrational overtones. The aqueous acid and the isolated diatomic molecule should be distinguished when specifying a dissociation process.^[ref]

Aqueous hydrogen iodide is strongly acidic, and iodide can also participate in reductive transformations. These roles must be separated when explaining a reaction.

A peroxide-containing product of ozone chemistry. In classical alkene ozonolysis, a secondary ozonide is converted to carbonyl products during a suitable workup.

A three-atom dipolar species formed in the classical Criegee account of ozonolysis. Recombination with a carbonyl compound can form a secondary ozonide.

A short-lived primary ozonide formed by ozone cycloaddition to an alkene. Fragmentation generates a carbonyl compound and a carbonyl oxide.

An organic sulfonyl chloride used to activate alcohol or oxime oxygen as a leaving group.

The compound $\mathrm{N}{\mathrm{H}}_2\mathrm{OH}$. Its nitrogen can add to carbonyl compounds, followed by dehydration to an oxime.

An oxime contains a $\mathrm{C}=\mathrm{N}-\mathrm{OH}$ group, commonly formed from a carbonyl compound and hydroxylamine. Unsymmetrical ketoximes can have distinct geometrical isomers.

Formation of an oxime O-sulfonate increases leaving-group ability at oxygen. Subsequent anti migration can proceed with N–O bond cleavage.

An oxime derived from a ketone. The two carbon substituents and the N–OH orientation determine which group can migrate in a stereospecific Beckmann rearrangement.

A planar six-membered aromatic ring with nitrogen at opposite ring sites. Its molecular point group is the D2h point group. The six ring $p_z$ atomic orbitals form a six-electron conjugated system; the in-plane nitrogen lone pairs are outside this $\pi$ basis.

A coordination complex with four carbon-bound cyanide ligands and a formal nickel(II), $d^8$, centre. Square planar molecular geometry permits a low-spin complex with no unpaired electrons.

An isolated boron trifluoride molecule has trigonal planar molecular geometry and the D3h molecular point group. Its three equal fluorine contributions give $I_{\parallel }=3m_{\mathrm{F}}{R}^2$ and $I_{\perp }=3m_{\mathrm{F}}{R}^2/2$ in the rigid rotor approximation.

A nitrogen-containing aromatic scaffold; redox-active derivatives produced by bacteria can affect ecological interactions and electron transfer.

A blue, redox-active phenazine produced by Pseudomonas aeruginosa. Its biological effects depend on redox conditions, concentration and local electron acceptors.

A coenzyme-A thioester carrying an acyl group, used in lipid metabolism and many other pathways.

A cyanogenic glucoside from sorghum whose pathway includes two P450 enzymes and a glucosyltransferase.

An acyl chloride contains $\mathrm{R}-\mathrm{C}(\mathrm{O})\mathrm{Cl}$. Addition of a nucleophile and chloride elimination is a common substitution pathway.

$\mathrm{PhCOCl}$.

$\mathrm{C}{\mathrm{H}}_3\mathrm{COCl}$, an acylating reagent that converts an alcohol into an acetate ester when HCl is suitably removed.

The acyl chloride $(\mathrm{C}{\mathrm{H}}_3{)}_2\mathrm{CHCOCl}$, with equivalent methyl groups in an achiral environment.

Methanesulfonic anhydride is $(\mathrm{MeS}{\mathrm{O}}_2{)}_2\mathrm{O}$, a reagent for making mesylates from alcohols.

A mesylate is a methanesulfonate, $\mathrm{ROS}{\mathrm{O}}_2\mathrm{Me}$. Converting an alcohol to its mesylate improves leaving-group ability without initially cleaving the original carbon–oxygen bond.

An alkenyl aluminate has an anionic aluminium-containing unit attached to an alkene carbon. Intramolecular oxygen coordination can close a five-membered ring in directed propargylic alcohol reductions.

Red-Al is sodium bis(2-methoxyethoxy)aluminium hydride. Suitable propargylic alcohols undergo oxygen-directed trans hydroalumination to cyclic alkenyl aluminate species; aqueous workup gives E allylic alcohols.

Osmium tetroxide adds to an alkene to form a cyclic osmate ester. Hydrolysis releases a vicinal diol; regeneration of Os(VIII) requires a reoxidant in a catalytic cycle.

Metachloroperbenzoic acid is a peroxycarboxylic acid used for concerted oxygen transfer to alkenes. A neighboring allylic hydroxyl can direct its approach through hydrogen bonding.

Decalin contains two fused six-membered carbon rings. Trans fusion permits a relatively rigid double-chair geometry, while cis fusion admits interconverting double-chair conformers.

An allenyl phosphine oxide contains an allene attached to a phosphine-oxide group. Attack at the central allene carbon can generate a carbanion on the adjacent phosphorus-bearing carbon, which is stabilized by the phosphoryl substituent.

Nitrobenzene is benzene bearing a nitro group. The nitro group withdraws electron density and stabilizes certain anionic aromatic addition intermediates.

Triflic anhydride is $(\mathrm{C}{\mathrm{F}}_3\mathrm{S}{\mathrm{O}}_2{)}_2\mathrm{O}$, an electrophilic sulfonylating reagent. carbonyl oxygen attack can form an O-triflylated intermediate; adjacent nitrogen donation gives an imidoyl-triflate description.

A carbamate contains the unit $\mathrm{O}-\mathrm{C}(\mathrm{O})-\mathrm{N}$. The nitrogen lone pair conjugates with the carbonyl; cyclic carbamates include 2-Oxazolidinone.

A chain arrangement implicated in cooperative carbon-dioxide capture in appropriate diamine-appended metal–organic frameworks. Framework spacing and proton transfer determine the actual adsorption mechanism.^[ref]

2-Oxazolidinone is the five-membered cyclic carbamate with ring path $\mathrm{O}-\mathrm{C}(\mathrm{O})-\mathrm{NH}-\mathrm{C}{\mathrm{H}}_2-\mathrm{C}{\mathrm{H}}_2$. Electrophilic activation of its carbonyl oxygen can generate an imidoyl-type electrophile.

A chloroformate has the connectivity $\mathrm{ClC}(\mathrm{O})\mathrm{OR}$. Nucleophilic addition at its carbonyl followed by chloride elimination makes a carbonate or carbamate.

Allyl chloroformate is $\mathrm{ClC}(\mathrm{O})\mathrm{OC}{\mathrm{H}}_2\mathrm{CH}=\mathrm{C}{\mathrm{H}}_2$. oxygen acylation of an enolate makes an allyl enol carbonate.

Dimethyl sulfoxide is a polar aprotic solvent. It supports reactions of anions with many organic electrophiles without providing an O–H proton.

Hexamethylphosphoramide has a strongly donating phosphoryl oxygen that coordinates lithium. It changes ion pairing and aggregate structures, often increasing the reactivity of anionic oxygen donors. It does not universally produce free monomeric anions.

An organolithium reagent contains a carbon–lithium interaction with substantial carbanionic carbon reactivity. Such reagents can act as bases or nucleophiles, and their solution aggregation affects both roles.

The lithium salt of an N-deprotonated enamine, stabilized by conjugation and often by aggregation.