| Ag | | |
| Ag | solute-volatilization interference
in flame spectroscopy |
| Ag+ | interfering substance
in electroanalytical chemistry |
| AgBr | | |
| AgBr | molecular rearrangement |
| AgCl | | |
| AgCl | gravimetric method |
| AgCl | gravimetric method |
| AgCl | gravimetric method |
| AgI | | |
| AgI | crystalline electrodes |
| α-AgI | polymorphic transition |
| β-AgI | polymorphic transition |
| AgNO3 | | |
| AgNO3 | gravimetric method |
| Ag2S | | |
| Ag2S | crystalline electrodes |
| Ag2S | crystalline electrodes |
| Al | | |
| Al | solute-volatilization interference
in flame spectroscopy |
| AlCl3 | | |
| AlCl3 | ionization |
| AlNb3 | | |
| Nb3Al | superconducting transition |
| Al2 | | |
| 2Al3+ | mean activity of an electrolyte in solution |
| Al2MgO4 | | |
| MgAl2O4 | solute-volatilization interference
in flame spectroscopy |
| Ar | | |
| Ar+ | diamond by CVD |
| Ar+ | diamond-like carbon films |
| Ar | cryogenic sampling |
| Ar | gas-filled phototube |
| Ar | Penning gas mixture |
| ArHOSe | | |
| ArSeOH | selenenic acids |
| As | | |
| As | poison in catalysis |
| As | photoconductive detector |
| AsH2 | | |
| H2As+ | arsanylium ions |
| AsH2O | | |
| H2As(=O)+ | arsanylium ions |
| AsH2O2 | | |
| HAs(OH)2 | arsonous acids |
| AsH3 | | |
| AsH3 | arsines |
| AsH3 | arsanes |
| AsH3O | | |
| H2AsOH | arsinous acids |
| H3As=O | arsine oxides |
| AsH3O2 | | |
| AsH3O2 | arsinic acids |
| AsH3O3 | | |
| AsH3O3 | arsonic acids |
| AsH4 | | |
| (H4As+) | onium compounds |
| AsH5 | | |
| AsH5 | arsoranes |
| As3H5 | | |
| H2AsAsHAsH2 | arsanes |
| As3H11 | | |
| H4AsAsH3AsH4 | arsanes |
| Au | | |
| Au | disproportionation |
| Au | disproportionation |
| 197Au | nuclear quadrupole moment (spectroscopic) |
| Au | disproportionation |
| AuFe | | |
| Au–Fe | spin-glass transition |
| BH | | |
| HB: | carbene analogues |
| HB+ | heteroconjugation |
| B2H | | |
| B–H–B | electron-deficient bond |
| B2H6 | | |
| B2H6 | electron-deficient bond |
| B5H9 | | |
| B5H9 | boranes |
| Ba | | |
| Ba2+ | mean activity of an electrolyte in solution |
| BaO3Ti | | |
| BaTiO3 | ferroelectric (antiferroelectric) transition |
| BiH3 | | |
| BiH3 | bismuthanes |
| BiH3 | bismuthines |
| BiH4 | | |
| (H4Bi+) | onium compounds |
| Br | | |
| Br | molecular rearrangement |
| Br | addition reaction |
| Br | sulfonium compounds |
| Br | fragmentation |
| Br | allylic substitution reaction |
| Br+ | halonium ions |
| Br | telomerization |
| Br− | leaving group |
| BrH | | |
| BrH | leaving group |
| BrH2 | | |
| (H2Br+) | onium compounds |
| C | | |
| C | methylotrophic microorganisms |
| 12C | relative micellar mass |
| –C= | heteroarenes |
| C | dipolar compounds |
| C | repulsive potential-energy surface |
| 12C | molecular ion in mass spectrometry |
| 13C | chemical shift,  in NMR |
| C | dipolar compounds |
| C | potential-energy (reaction) surface |
| C | dipolar compounds |
| C | dipolar compounds |
| C | multiply labelled |
| C | dipolar compounds |
| C | tautomerism |
| C | transferases |
| CB | | |
| BC | repulsive potential-energy surface |
| B–C | potential-energy (reaction) surface |
| CBrCl3 | | |
| CBrCl3 | telomerization |
| CBr4 | | |
| CBr4 | rotator phase transition |
| CCaO3 | | |
| CaCO3 | monotropic transition |
| CaCO3 | monotropic transition |
| CCl | | |
| C–Cl | coordination |
| CClF3 | | |
| CF3Cl | background concentration (level)
in atmospheric chemistry |
| CCl2 | | |
| CCl2 | α-addition (alpha-addition) |
| :CCl2 | carbenes |
| CCl2F2 | | |
| CF2Cl2 | background concentration (level)
in atmospheric chemistry |
| CCl3 | | |
| Cl3C. | chain transfer |
| CCl3 | telomerization |
| Cl3C− | carbanion |
| Cl3C. | telomerization |
| CH | | |
| –CH= | dipyrrins |
| C–H | steric isotope effect |
| C–H | σ, π (sigma, pi) |
| CH | carbaboranes |
| –CH= | quinones |
| C–H | persistent |
| HC… | carbynes |
| C–H | symbiosis |
| CH | agostic |
| CHN | | |
| HC≡N | cyanides |
| HC≡N | nitriles |
| C=NH | imines |
| HN+≡C− | isocyanides |
| HC≡N | isocyanides |
| CHNO | | |
| HOC≡N | cyanates |
| HON=C: | fulminates |
| HOC≡N | isocyanates |
| HC≡N+–O− | fulminates |
| HN=C=O | isocyanates |
| CHNS | | |
| HSC≡N | thiocyanates |
| CHNSe | | |
| HSeCN | selenocyanates |
| CHO | | |
| –CHO | characteristic group in organic nomenclature |
| CHO2 | | |
| –COOH | characteristic group in organic nomenclature |
| CH2 | | |
| H2C: | alkylidenes |
| CH2 | insertion |
| –CH2– | pyrromethenes |
| H2C | silylene |
| H2C.+ | carbynium ions |
| H2C: | carbenes |
| H2C.+ | carbene radical cations |
| :CH2 | carbenes |
| CH2 | tropylium ions |
| –CH2– | meso structures in polymers |
| CH2 | tropyl radicals |
| CH2 | homoconjugation |
| –CH2– | hydrocarbylene groups |
| CH2Cl | | |
| ClCH2– | organyl groups |
| CH2N2 | | |
| CH2=N2 | diazo compounds |
| CH2=N=N | isoelectronic |
| HN=C=NH | carbodiimides |
| CH2Na2O4 | | |
| Na2CO3.10H2O | efflorescence |
| CH2O | | |
| CH2O | smog chamber in atmospheric chemistry |
| CHOH | oxo compounds |
| CH2O | fragmentation |
| CHOH | prochirality |
| CH3 | | |
| CH3 | allylic intermediates |
| .CH3 | radical (free radical) |
| CH3+ | even-electron ion |
| CH3 | dimerization |
| CH3 | σ, π (sigma, pi) |
| CH3 | fragmentation |
| CH3 | benzylic intermediates |
| CH3 | chain reaction |
| CH3 | chain reaction |
| CH3 | dimerization |
| CH3 | fragmentation |
| CH3 | colligation |
| CH3 | abstraction |
| CH3 | bond-dissociation energy,  |
| CH3Cl | | |
| CH3Cl | substitution reaction |
| CH3Cl | molecular rearrangement |
| CH3ClO2S | | |
| CH3ClO2S | acyl halides |
| CH3F | | |
| CH3F | molecular laser |
| CH3I | | |
| CH3I | identity reaction |
| CH3IMg | | |
| MeMgI | organometallic compounds |
| CH3N | | |
| CH3N: | carbene analogues |
| CH3N: | nitrenes |
| CH3NO2 | | |
| CH3NO2 | carbamates |
| CH3NO2 | azinic acids |
| CH3NO2S | | |
| CH3N=S(=O)2 | sulfonylamines |
| CH3NaS | | |
| CH3S−Na+ | thiolates |
| CH3O | | |
| –CH2OH | uronic acids |
| OCH3 | π-electron acceptor/donor group |
| CH3O+ | oxylium ions |
| CH3S | | |
| CH3S. | sulfenyl radicals |
| MeS– | organyl groups |
| CH3–S– | sulfenyl groups |
| CH3S+ | sulfenylium ions |
| CH4 | | |
| CH4 | bond-dissociation energy, |
| CH4 | stoichiometry |
| CH4 | molecular entity |
| 12CH4+ | isotope pattern in mass spectrometry |
| CH4 | reduced species |
| CH4 | bond energy (mean bond energy) |
| CH4 | multiply labelled |
| CH4 | bond energy (mean bond energy) |
| CH4 | composition of pure air in atmospheric chemistry |
| CH4 | symbiosis |
| CH4 | spectator mechanism |
| CH4 | isotopologue |
| CH4 | isotope pattern in mass spectrometry |
| 13CH4+ | isotope pattern in mass spectrometry |
| CH4 | abstraction |
| CH4N2O | | |
| CH4N2O | isoureas |
| CH4N4 | | |
| H2NN=CHN=NH | formazans |
| CH4O | | |
| CH4O | line formula |
| CH4O | oxidative coupling |
| CH3OH | Brønsted acid |
| CH4O | α-addition (alpha-addition) |
| (CH3OH2+) | lyonium ion |
| CH3OH | amphiprotic (solvent) |
| CH4O | substitution reaction |
| CH4O4 | | |
| C(OH)4 | ortho acids |
| CH4Si | | |
| H2Si=CH2 | heteroalkenes |
| CH5 | | |
| +CH5 | alkanium ions |
| CH5+ | coordination number |
| CH5B | | |
| CH5B | spectator mechanism |
| CH5N3O | | |
| NH2NHC(=O)NH2 | semicarbazones |
| CH5P | | |
| CH3PH2 | phosphines |
| CIN | | |
| ICN | pseudohalogens |
| CKN | | |
| KCN | order-disorder transition |
| KCN | order-disorder transition |
| CKNO | | |
| KOCN | cyanates |
| CN | | |
| C–N | hydrolases |
| CN− | prochirality |
| –C≡N | characteristic group in organic nomenclature |
| C–N | ligases (synthetases) |
| C–N | lyases |
| –CN | carbonitriles |
| CN− | order-disorder transition |
| CN− | interfering substance
in electroanalytical chemistry |
| CN− | pseudohalogens |
| CNNa | | |
| NaCN | cyanides |
| CNNaO | | |
| Na+[–C≡N+O−] | fulminates |
| CNO | | |
| –NCO | characteristic group in organic nomenclature |
| CNS | | |
| SCN− | pseudohalogens |
| N≡C–S− | organoheteryl groups |
| CNS2 | | |
| (SCN)2 | pseudohalogens |
| CO | | |
| C=O | carbonyl compounds |
| C–O | ligases (synthetases) |
| C–O | lyases |
| CO | isoelectronic |
| CO | oxocarbons |
| –C(=O)– | quinones |
| CO | air pollutant |
| C–O | hydrolases |
| C=O | oxo compounds |
| CO2 | | |
| CO2 | carbon dioxide laser (CO2
laser) |
| CO2 | laser |
| CO2 | sublimation |
| CO2 | photosynthesis |
| CO2 | reduced species |
| CO2 | greenhouse effect in atmospheric chemistry |
| O=C=O | heterocumulenes |
| CO2 | sanitary land fill |
| CO2 | photosynthesis |
| CO2 | photophosphorylation |
| CO2 | cryogenic sampling |
| O=C=O | oxocarbons |
| CO2 | acid rain in atmospheric chemistry |
| CO2 | sublimation |
| CO2 | molecular laser |
| CO2 | carbon dioxide laser (CO2
laser) |
| CO2 | composition of pure air in atmospheric chemistry |
| CO2 |
CO2
laser |
| CS | | |
| C–S | ligases (synthetases) |
| CY | | |
| C–Y | bisecting conformation (eclipsing conformation) |
| C2 | | |
| C–C | ligases (synthetases) |
| C–C | orbital symmetry |
| C–C | hydrolases |
| C–C | symbiosis |
| C–C | lyases |
| C–C | eclipsing strain |
| C2H | | |
| HC≡C− | carbanion |
| C2HNa | | |
| NaC≡CH | acetylides |
| C2H2 | | |
| H2C=C: | vinylidenes |
| –CH=CH– | heteroarenes |
| C2H2 | flow rate
in flame emission and absorption spectrometry |
| C2H2 | local fraction atomized,
 ,
in flame emission and absorption spectrometry |
| H2C=C: | carbenes |
| C2H2O | | |
| CH2=C=O | heterocumulenes |
| CH2=C=O | isoelectronic |
| C2H3 | | |
| CH2=CH– | vinylic groups |
| C2H3AgO2 | | |
| C2H3AgO2 | molecular rearrangement |
| C2H3Cl | | |
| C2H3Cl | isodesmic reaction |
| :Cl–CH=CH2 | conjugated system (conjugation) |
| C2H3ClO | | |
| C2H3ClO | acyl halides |
| C2H3Cl3 | | |
| C2H3Cl3 | isodesmic reaction |
| C2H3N | | |
| CH3C≡N | cyanides |
| C2H3NS | | |
| CH3SC≡N | thiocyanates |
| C2H3O | | |
| CH3C(=O)– | organyl groups |
| C2H3O2 | | |
| CH3CO2− | Brønsted base |
| –CH2CO2H | prochirality |
| C2H3O2 | ionization |
| C2H3O2 | nucleophilic catalysis |
| C2H3O2 | proton transfer reaction |
| C2H4 | | |
| C2H4 | disproportionation |
| C2H4 | attachment |
| C2H4 | isodesmic reaction |
| C2H4 | reactive adsorption |
| C2H4 | ene reaction |
| –CH2–CH2– | meso structures in polymers |
| C2H4 | hydration |
| +CH2–+CH2 | dicarbenium ions |
| C2H4 | sorptive insertion in surface catalysis |
| C2H4 | hyperconjugation |
| C2H4Cl2 | | |
| C2H4Cl2 | isodesmic reaction |
| C2H4Cl2NO | | |
| (ClCH2)2N–O. | nitroxides |
| C2H4Cl2NO | aminoxyl radicals |
| C2H4Cl2O | | |
| C2H4Cl2O | α-addition (alpha-addition) |
| C2H4Cl3Pt | | |
| [PtCl3(CH2=CH2)]− | chelation |
| C2H4F | | |
| C2H4F | hyperconjugation |
| C2H4N | | |
| CH3–CH=N. | iminyl radicals |
| C2H4O | | |
| C2H4O | stoichiometry |
| C2H4O2 | | |
| CH3CO2H | Brønsted acid |
| C2H4O2 | ionization |
| C2H4O2 | proton transfer reaction |
| C2H4O2 | catalytic hydrogenolysis |
| C2H4O2 | nucleophilic catalysis |
| C2H4O2 | leaving group |
| CH3CO2H | prochirality |
| C2H4O3 | | |
| CH3C(=O)OOH | peroxy acids |
| CH3C(=O)OOH | per acids |
| C2H5 | | |
| C2H5 | disproportionation |
| C2H5 | disproportionation |
| CH3CH2+ | carbenium ion |
| CH3CH2– | organyl groups |
| C2H5Br | | |
| 13CCH5Br+. | isotopic molecular ion |
| C2H579Br | molecular ion in mass spectrometry |
| C2H581Br+. | isotopic molecular ion |
| 13C2H581Br+. | isotopic molecular ion |
| C2H5BrO | | |
| BrCH2CH2OH | halohydrins |
| C2H5Cl | | |
| C2H5Cl | nucleophile (nucleophilic) |
| C2H5N | | |
| MeN=CH2 | heteroalkenes |
| C2H5NO2 | | |
| H3N+CH2C(=O)O− | zwitterionic compounds/zwitterions |
| C2H5N3O2 | | |
| H2NNHC(=O)C(=O)NH2 | semioxamazones |
| C2H6 | | |
| C2H6 | disproportionation |
| CH313CH3 | principal ion in mass spectrometry |
| C2H6 | catalytic hydrogenolysis |
| C2H6 | pseudorotation |
| C2H6 | dimerization |
| C2H6 | catalytic hydrogenolysis |
| C2H6 | catalytic hydrogenolysis |
| C2H6CuLi | | |
| Li+[CuMe2]− | organometallic compounds |
| C2H6NO | | |
| C2H6NO | aminoxides |
| C2H6N2 | | |
| C2H6N2 | carboxamidines |
| C2H6N2 | isoelectronic |
| C2H6N4S2 | | |
| H2NC(=NH)SSC(=NH)NH2 | formamidine disulfides |
| C2H6O | | |
| CH3CH2OH | constitutional isomerism |
| CH3OCH3 | constitutional isomerism |
| CH3–CH2–[18O][2H] | mixed labelled |
| CH3CH2OH | prochirality |
| C2H6O | hydration |
| CH3–CH[2H]–OH | singly labelled |
| C2H6O2 | | |
| HOCH2CH2OH | glycols |
| C2H6S | | |
| MeCH2SH | thiols |
| C2H7 | | |
| [C2H7]+ | alkanium ions |
| C2H7As | | |
| CH3CH2AsH2 | arsines |
| C2H7AsO2 | | |
| C2H7AsO2 | arsinic acids |
| C2H7NS | | |
| C2H5SNH2 | sulfenamides |
| CH3CH2SNH2 | amides |
| C2H7S | | |
| (CH3)2S+H | onium compounds |
| C2H10O3Si3 | | |
| C2H10O3Si3 | cyclosiloxanes |
| C2N | | |
| (CN)2 | pseudohalogens |
| C3 | | |
| C=C=C | chirality axis |
| C3H3AsO | | |
| (CH3)3As=O | arsine oxides |
| C3H3Bi | | |
| (CH3)3Bi | bismuthines |
| C3H3N | | |
| CH2=CH–C≡N | conjugated system (conjugation) |
| C3H4 | | |
| H2C=CHC:H | vinyl carbenes |
| H2C=CHCH: | carbenes |
| C3H5 | | |
| CH2=CHCH2 | allylic groups |
| CH3CH2C… | alkylidynes |
| C3H5 | delocalization |
| C3H5 | delocalization |
| H2C=CHCH2+ | allylic intermediates |
| C3H5NO | | |
| HOCH2CH2C≡N | cyanohydrins |
| C3H5NO | lactams |
| C3H5NO3 | | |
| C3H5NO3 | amic acids |
| C3H5NO3S | | |
| C3H5NO3S | imides |
| C3H5NSe | | |
| CH3CH2SeCN | selenocyanates |
| C3H5O | | |
| C3H5O | abstraction |
| C3H5O | contributing structure |
| C3H5O | contributing structure |
| C3H6 | | |
| CH3CH2CH: | alkylidenes |
| C3H6 | ene reaction |
| H2C.–CH2–C.H2 | diradicals |
| –CH2CH2CH2– | hydrocarbylene groups |
| C3H6 | corrinoids (cobalamines, corphyrins, corrins, vitamin B12
compounds)
|
| +CH2CH2–+CH2 | dicarbenium ions |
| C3H6.+ | radical ion |
| C3H6O | | |
| C3H6O | abstraction |
| C3H6O | proton transfer reaction |
| C3H6O | dimerization |
| C3H6O | isoelectronic |
| C3H6O | dimerization |
| C3H6O | epoxy compounds |
| C3H6O | Paterno–Büchi reaction |
| C3H6O | fragmentation |
| C3H6S | | |
| CH3CH2C(=S)H | thioaldehydes |
| C3H7 | | |
| CH3CH2CH2+ | carbenium ion |
| CH3CH2C.H2 | alkyl radicals |
| C3H7Br | | |
| C3H7Br | molecular rearrangement |
| C3H7ClO | | |
| ClCH2CH2CH2OH | halohydrins |
| C3H7N | | |
| EtCH=NH | aldimines |
| C3H7O | | |
| C3H7O | proton transfer reaction |
| C3H7O | fragmentation |
| C3H8 | | |
| C3H8 | catalytic hydrogenolysis |
| C3H8O2S | | |
| C2H5S(=O)2CH3 | sulfones |
| (CH3)2CHS(=O)OH | sulfinic acids |
| C3H9ClP | | |
| Cl(CH3)3P+ | onium compounds |
| C3H9ClS | | |
| [(CH3)3S]+Cl− | sulfonium compounds |
| C3H9N | | |
| C3H9N | leaving group |
| NMe3 | leaving group |
| C3H9N | ammoniumyl radical ions |
| C3H9NO | | |
| (CH3)3N+–O− | zwitterionic compounds/zwitterions |
| C3H9NO2S | | |
| C3H9NO2S | amides |
| C3O2 | | |
| O=C=C=C=O | heterocumulenes |
| O=C=C=C=O | oxocarbons |
| C4H4N2 | | |
| C4H4N2 | pyrimidine bases |
| C4H4N2 | heteroarenes |
| C4H4O2 | | |
| C4H4O2 | isolated double bonds |
| HO[CH2]4OH | glycols |
| C4H4S | | |
| C4H4S | heteroarenes |
| C4H5N | | |
| C4H5N | indicated hydrogen |
| C4H5NO2 | | |
| C4H5NO2 | imides |
| C4H6 | | |
| C4H6 | attachment |
| C4H6 | cheletropic reaction |
| C4H6 | s-cis, s-trans |
| CH2=C(C.H2)2 | trimethylenemethanes |
| CH3–CH=C=CH2 | dienes |
| C4H6 | addition reaction |
| CH2=CH–CH=CH2 | conjugated system (conjugation) |
| CH2=CH–CH=CH2 | dienes |
| C4H6 | s-cis, s-trans |
| C4H6Br2 | | |
| C4H6Br2 | addition reaction |
| C4H6Br2 | addition reaction |
| C4H6O | | |
| C4H6O | oxa-di-π-methane rearrangement |
| C4H6O | oxa-di-π-methane rearrangement |
| C4H6O2S | | |
| C4H6O2S | cheletropic reaction |
| C4H6O3 | | |
| C4H6O3 | acid anhydrides |
| C4H6O3 | nucleophilic catalysis |
| C4H6O4 | | |
| C4H6O4 | oxidative coupling |
| C4H6O6 | | |
| C4H6O6 | meso-compound |
| C4H7Br | | |
| C4H7Br | allylic substitution reaction |
| C4H7ClO2Zn | | |
| ClZnCH2C(=O)OEt | organometallic compounds |
| C4H7NO | | |
| (CH3)2C(OH)C≡N | cyanohydrins |
| C4H7Y | | |
| C4H7Y | chain polymerization |
| C4H8 | | |
| C4H8 | addition reaction |
| C4H8 | anti |
| C4H8 | hyperconjugation |
| C4H8 | cycloalkanes |
| C4H8Br2 | | |
| C4H8Br2 | anti |
| C4H8O | | |
| CH3CH2COCH3 | prochirality |
| C4H8O | multiply labelled |
| C4H8O | allylic substitution reaction |
| C4H8O | allylic substitution reaction |
| C4H8S | | |
| CH3C(=S)CH2CH3 | thioketones |
| C4H9 | | |
| C4H9 | hyperconjugation |
| C4H9Br | | |
| C4H9Br | addition reaction |
| C4H9FO | | |
| C4H9FO | diastereotopic |
| C4H9FO | diastereotopic |
| C4H9N | | |
| C4H9N | pre-equilibrium (prior equilibrium) |
| C4H9O | | |
| C4H9O | fragmentation |
| C4H10 | | |
| C4H10 | catalytic hydrogenolysis |
| C4H10 | catalytic hydrogenolysis |
| C4H10 | catalytic hydrogenolysis |
| C4H10Mg | | |
| Et2Mg | organometallic compounds |
| C4H10N | | |
| C4H10N | pre-equilibrium (prior equilibrium) |
| C4H10O | | |
| CH3CHOHCH2CH3 | prochirality |
| C4H10O | fragmentation |
| CH3CH2OCH2CH3 | ethers |
| C4H10O | diastereotopic |
| CH3CH2CHOHCH3 | prochirality |
| C4H10O3 | | |
| HC(OCH3)3 | ortho esters |
| C4H11N | | |
| (CH3)3N+–C−H2 | ylides |
| C4H11NO | | |
| C4H11NO | pre-equilibrium (prior equilibrium) |
| C4H11O3PS | | |
| C4H11O3PS | betaines |
| C4H12N2 | | |
| C4H12N2 | amine imides |
| C4H12Si | | |
| SiMe4 | chemical shift, in NMR |
| SiMe4 | chemical shift, in NMR |
| SiMe4 | chemical shift, in NMR |
| C4H13NO | | |
| [(CH3)4N]+OH− | quaternary ammonium compounds |
| C4O4 | | |
| C4O4 | oxocarbons |
| C5 | | |
| C5 | terpenes |
| C5H3BrN4 | | |
| C5H3BrN4 | tele-substitution |
| C5H4 | | |
| C5H4 | electrocyclic reaction |
| C5H4N2O | | |
| C5H4N2O | topomerization |
| C5H4N2O | topomerization |
| C5H4N4 | |
