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Alpha-ketoglutarate is another name for 2-Oxoglutarate, a five-carbon dicarboxylate containing a ketone adjacent to a carboxylate group. The names describe the same carbon skeleton using two positional naming conventions.

Alpha-ketoglutarate links the citric acid cycle with amino acid metabolism: transamination interconverts its carbon skeleton with that of glutamic acid. Its oxidative decarboxylation yields succinyl-CoA and carbon dioxide.^[ref]

Isocitrate is a six-carbon tricarboxylate related to citrate by the position of a hydroxyl group. This change makes the hydroxyl-bearing carbon available for oxidation.

In the citric acid cycle, oxidative decarboxylation of isocitrate produces 2-Oxoglutarate, releases carbon dioxide, and reduces a nicotinamide cofactor. Isomerization therefore prepares a carbon skeleton for a reaction that its original arrangement does not readily undergo.^[ref]

Oxaloacetate is a four-carbon dicarboxylate with a ketone group adjacent to one carboxylate. It is regenerated in the citric acid cycle rather than consumed as a net reactant on every turn.

Condensation with acetyl-CoA forms citrate; later oxidation of malate regenerates oxaloacetate. Removing oxaloacetate for biosynthesis therefore requires replenishing the cycle's intermediates to sustain flux.^[ref]

Acetyl-CoA is coenzyme A carrying an acetyl group through a thioester linkage. It is a central two-carbon donor in metabolism.

Condensation of acetyl-CoA with oxaloacetate forms citrate at the beginning of the citric acid cycle. The same carrier also supplies carbon for biosynthetic pathways, so its fate depends on the cell's metabolic state.^[ref]

Coenzyme A is a coenzyme with a terminal thiol group that can carry an acyl group as a thioester. Its nucleotide-containing portion is recognized by enzymes, while the sulfur-linked group participates in chemical transformations.

Acetyl-CoA and succinyl-CoA carry different acyl units on the same coenzyme framework. This reuse of a molecular carrier connects fatty acid metabolism with the citric acid cycle.^[ref]

p-xylene is 1,4-dimethylbenzene, ${\mathrm{C}}_6{\mathrm{H}}_4(\mathrm{C}{\mathrm{H}}_3{)}_2$. Its two methyl substituents occupy opposite positions on the benzene ring.

It has the same molecular formula as the ortho and meta isomers but a different molecular symmetry and packing behavior. Comparing these isomers illustrates why a formula is insufficient to predict every physical property of an aromatic compound.

Cyclohexane is the cyclic alkane ${\mathrm{C}}_6{\mathrm{H}}_{12}$. Its preferred chair conformation allows near-tetrahedral bond angles and largely staggered neighboring bonds.

Ring flips exchange axial and equatorial positions. Consequently a substituent can retain its up/down orientation while changing the steric interactions that determine conformational preference and reaction accessibility.

Alcohols such as ethanol and glycerol contain hydroxy groups on carbon chemical atoms with only single covalent bonds.

Succinate is the dianion of succinic acid, a four-carbon dicarboxylic acid with structure ${}^{-}\mathrm{OOC}-\mathrm{C}{\mathrm{H}}_2-\mathrm{C}{\mathrm{H}}_2-\mathrm{CO}{\mathrm{O}}^{-}$. It is an intermediate of the citric acid cycle.

Succinate dehydrogenase oxidizes succinate to fumarate, creating a carbon-carbon double bond while passing reducing equivalents into the respiratory machinery. This connects carbon-skeleton chemistry with electron transfer.

Ubiquinone is a membrane-soluble quinone electron carrier with a hydrophobic isoprenoid side chain. Reduction of the quinone headgroup gives ubiquinol.

In the mitochondrial respiratory chain, movement within the membrane transfers reducing equivalents between protein complexes. The hydrophobic chain controls localization, while the headgroup carries out the redox chemistry.

Propidium iodide is a nucleic acid stain used in a flow cytometric DNA-content assay; ribonuclease A removes interfering RNA.^[ref]

Sodium thiosulfate is the salt $\mathrm{N}{\mathrm{a}}_2{\mathrm{S}}_2{\mathrm{O}}_3$, often encountered as a hydrate. Its thiosulfate ion can participate in both oxidation-reduction reactions and metal-ion complex formation.

In photographic fixing, thiosulfate binds silver and helps dissolve residual silver halide. In analytical chemistry, reaction with iodine supports quantitative titration. These applications use different aspects of the same anion's chemistry.

Zinc sulfide is $\mathrm{ZnS}$, a semiconductor compound with common cubic and hexagonal structural forms. Sphalerite is the familiar cubic mineral form.

Its optical response depends on crystal structure, defects, and dopants. Zinc sulfide therefore illustrates why luminescence is often a property of a carefully prepared material rather than a prediction from the bare formula alone.

A silver halide is a compound of silver with a halogen, commonly represented as AgX for a monovalent halide. Silver bromide, silver chloride, and silver iodide are important examples.

Several silver halides are photosensitive. Light-generated charge can initiate formation of tiny silver-rich centres in a photographic grain, and chemical development amplifies the latent change into a visible image. This connects a microscopic photochemical event with macroscopic image formation.

An oxide is a compound in which oxygen is combined with another element, usually with oxygen formally in oxidation state $-2$. Ionic metal oxides and covalent nonmetal oxides can have very different structures.

For example, magnesium oxide is a lattice solid, whereas carbon dioxide is molecular. Peroxides contain an oxygen-oxygen unit with a different oxidation-state assignment, so they should not be treated as ordinary oxides merely because they contain oxygen.

Cadmium chloride is conventionally written $\mathrm{CdC}{\mathrm{l}}_2$, with cadmium in oxidation state +2. Solid and hydrated forms must be distinguished from dissolved cadmium-chloride species.

In chemical solution, chloride concentration can change the coordination environment around cadmium. A bulk formula therefore specifies overall composition without uniquely specifying every molecular or ionic species present.

Tetrachloroethylene is $\mathrm{C}{\mathrm{l}}_2\mathrm{C}=\mathrm{CC}{\mathrm{l}}_2$, a chlorinated molecular liquid. Its four chlorine atoms supply a large chlorine inventory per molecule.

In the Homestake experiment, tetrachloroethylene served as a target for detecting solar neutrinos through a rare chlorine-to-argon nuclear transformation. The solvent's chemical identity determines the target inventory, while the observed conversion is a nuclear process.

Gallium arsenide is the binary semiconductor $\mathrm{GaAs}$, containing one gallium atom per arsenic atom in its ideal composition. Its common zinc-blende-related structure is distinct from a simple mixture of elemental gallium and arsenic.

Its direct band gap supports optical transitions useful in emitters and photodetectors. Crystal defects, doping, and interfaces affect device behaviour in addition to the bulk chemical formula.

Gadolinium sulfate octahydrate is the hydrated salt $\mathrm{G}{\mathrm{d}}_2(\mathrm{S}{\mathrm{O}}_4{)}_3\cdot 8{\mathrm{H}}_2\mathrm{O}$. Gadolinium(III) ions provide localized magnetic moments, while water of crystallization is part of the crystal composition.

The material was used in the Giauque-MacDougall magnetic cooling experiment. Changing the magnetic field under suitable thermal isolation changes the spin entropy and the temperature, connecting the salt's microscopic magnetic states with refrigeration.

Gadolinium antimonide is the binary compound $\mathrm{GdSb}$, with a rock-salt-related crystal structure. Its low-temperature antiferromagnetism and electronic transport make it useful for studying the relation between magnetic order and electronic bands.

Epitaxial thin films allow strain and thickness to be varied while measuring transport or photoemission. This separates changes caused by the host composition from those produced by its crystalline environment.^[ref]