Periodic Table |
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Lewis Acid/Base Interaction Matrix Database
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Lobe-HOMO Lewis Bases

Electron Lone Pair Species | Search for Lobe-HOMO Lewis base species in The Chemical Thesaurus |
FMO Topology: |
Typical electron lone pair species in which the Lewis base HOMO is a px FMO orbital. In valence bond terms, the electron pair is in an sp3, sp2 or sp hybrid orbital. On complexation species show directional bonding which implies that the HOMO is directional, ie lobe shaped. |
Charge: | Negative or neutral with a lone-pair of electrons. |
HSAB: |
Species range
from hard to soft. The hardness of anionic Lobe-HOMO Lewis bases
can be defined with respect to the methyl anion, H3C the carbon-hydrogen bond length in methane (109pm). All Lobe-HOMO Lewis bases can by definition be protonated and the conjugate Brønsted acid's proton-to-Lewis base bond length, along with its pKa value, serves to probe the Lewis base's chemistry and behaviour. Bond-length and pKa data are linear over congeneric series and planars. Methane, CH4, is a convenient reference Lobe-HOMO Lewis base due to the importance of carbon in organic chemistry and that so many reactions occur at carbon centres. Congeneric species with base-to-H+ bond lengths shorter than 109pm, such as the hydroxide ion HO (HO–H bond length = 96pm), are deemed to be harder than the methyl carbanion. Longer bond-length as seen with iodide, I, (HI bond length = 161pm) equates with softness. |
Chemistry: |
Lobe-HOMO Lewis bases are the classic electron lone-pair donor species that can act as:
Lewis acid/base complexes formed by Lobe-HOMO Lewis bases range from FMO controlled covalent carbon-carbon bonds to charge-controlled ionic species such as cesium fluoride, CsF. The atomic lone pair centre may be embedded in a π-system, for example the allyl ion, in which case the species can be dual classified as a Lobe-HOMO and a π-HOMO Lewis base. When the species reacts via a single atomic centre it is classified as a Lobe-HOMO Lewis base. There are several subclasses of Lobe-HOMO Lewis bases, including:
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Congeneric Series: |
There are two important congeneric planars to be found within electronegative main group elements and their anions. One is formed by the X anions and the other by X: neutral lone pair species. Read more about the chemistry of these congeneric planars elsewhere in this webbook, here: ![]() |
The Inerts |
A number of Group 14 elemental hydrides: CH4, SiH4, GeH4& SnH4, are rather inert towards Lewis acid and Lewis base reagents. (Species can be oxidised and they are susceptible to attack by radicals and diradicals.) However, methane can be protonated by super acids to the carbonium ion: H+ + CH4 > [CH5]+ So methane is a Lewis base but, like helium, it is an exceedingly feeble proton abstractor. It follows that: CH4, SiH4, GeH4, SnH4 and related compounds are Lewis bases. Search for inert species in The Chemical Thesaurus |
Lobe-HOMO Lewis base (generic)![]() |
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Acetal (generic) more here |
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Acetal, cyclic (generic) more here |
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Acetaldehyde enolate more here |
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Acetate ester (generic) more here |
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Acetate ion more here |
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Acetylide anion (generic) more here |
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Acrylate ion more here |
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Alcohol (generic) more here |
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1° Alcohol (generic) more here |
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1° Alcohol, R-CH2CH2OH (generic) more here |
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2° Alcohol (generic) more here |
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2° Alcohol, cyclohexyl (generic) more here |
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3° Alcohol (generic) more here |
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Aldehyde (generic) more here |
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Aldehyde stabilised carbanion (generic) more here |
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Aldehyde, alpha-hydrogen (generic) more here |
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Alkenyl lithium (generic) more here |
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Alkoxide (generic) more here |
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1° Alkoxide ion (generic) more here |
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2° Alkoxide ion (generic) more here |
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3° Alkoxide ion (generic) more here |
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3-Alkoxy propanoate, alkyl (generic) more here |
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Alkyl bromide (generic) more here |
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Alkyl chloride (generic) more here |
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Alkyl lithium (generic) more here |
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Alkyl nitrile alpha-carbanion (generic) more here |
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Allyl alkoxide ion more here |
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1° Allylic alcohol (generic) more here |
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2° Allylic alcohol (generic) more here |
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1° Amide (generic) more here |
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1° Amide, anion (generic) more here |
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2° Amide (generic) more here |
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3° Amide (generic) more here |
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Amide ion more here |
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Amidosulfate anion more here |
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1° Amine (generic) more here |
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1° Amine, 1° alkyl (generic) more here |
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2° Amine (generic) more here |
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2 Amine, (RCH2)2NH (generic) more here |
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2° Amine, R, R- (generic) more here |
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3° Amine (generic) more here |
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3° Amine, (RCH2)3N (generic) more here |
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Ammonia more here |
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Ammonia 0.880 more here |
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Ammonia, aqueous more here |
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Aniline more here |
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Aniline, N-2° alkyl (generic) more here |
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Aniline, N-alkyl (generic) more here |
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Anionic Lobe-HOMO Lewis base congeneric planar more here |
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Anisole more here |
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Aqueous alkali, 0.05 to 1.0 molar (generic) more here |
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Argon more here |
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Arsenate (dihydrogen) ion more here |
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Arsenate (hydrogen) ion more here |
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Arsenide ion more here |
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Arsenite ion more here |
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Arsinate ion more here |
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Arsine more here |
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Arsine anion more here |
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Arsine anion (generic) more here |
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Arsine, trialkyl (generic) more here |
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Azide ion more here |
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Aziridine more here |
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Base, charged (generic) more here |
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Base, neutral (generic) more here |
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Benzoate ion more here |
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Benzoic acid more here |
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Benzyl alcohol (generic) more here |
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Benzyl anion more here |
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Benzyl anion (generic) more here |
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Bicarbonate ion more here |
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Bisulfite ion more here |
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Borate ion more here |
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Brønsted acid, hydroxy (generic) more here |
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Bromate ion more here |
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Bromide ion more here |
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2-Butanol more here |
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tertiary Butanol more here |
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tertiary Butyl alkoxide more here |
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tertiary Butyl carbanion more here |
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Carbanion (generic) more here |
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1° Carbanion (generic) more here |
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2° Carbanion (generic) more here |
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3° Carbanion (generic) more here |
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Carbanion, stabilised (generic) more here |
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Carbide ion more here |
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Carboiimide (generic) more here |
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Carbon dioxide more here |
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Carbon monoxide more here |
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Carbonate diester (generic) more here |
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Carbonate ion more here |
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Carbonyl function (generic) more here |
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Carboxylate dianion (generic) more here |
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Carboxylate ion (generic) more here |
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Carboxylic acid (generic) more here |
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Chlorate ion more here |
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Chloride ion more here |
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Chlorine diiodide ion more here |
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Chlorite ion more here |
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beta-Chloroethyl amine (generic) more here |
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beta-Chloroethyl ether (generic) more here |
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beta-Chloroethyl thioether (generic) more here |
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Chromate ion, hydrogen more here |
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Chromate(VI) ion more here |
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18-Crown-6 more here |
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Cumulene (generic) more here |
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Cyanamide ion more here |
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Cyanate ion more here |
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Cyanide ion more here |
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Cyanohydrin, alkyl (generic) more here |
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Cyclopropane carboxylate ion more here |
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Cyclopropenyl anion more here |
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Cyclopropyl anion more here |
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Deuterium oxide more here |
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Dialkyl arsine (generic) more here |
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Dichromate(VI) ion more here |
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Diglyme more here |
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Dihydrogen phosphate ion more here |
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beta-Diketone anion (generic) more here |
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beta-Diketone (generic) more here |
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Dimethyl ether more here |
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Dimethylamide anion more here |
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Dimethylamine more here |
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N,N-Dimethyl aniline more here |
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Dimethylsulfoxide more here |
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Dimethylsulfoxide anion more here |
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Dimethylthioether more here |
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trans 1,2-Diol (generic) more here |
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Diphenyl amide anion more here |
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Diphenyl ether more here |
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Diphenylamine more here |
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Diphenylmethyl anion more here |
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Disulfide (hydrogen) ion more here |
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Disulfide anion, organic (generic) more here |
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Disulfide dianion more here |
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Disulfide, organic (generic) more here |
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Disulfite ion more here |
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1,3-Dithiane anion (generic) more here |
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1,2-Dithioethane dianion more here |
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Dithionate ion more here |
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Dithionite ion more here |
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Enamine anion (generic) more here |
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Enolate anion (generic) more here |
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Epoxide (generic) more here |
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Ester (generic) more here |
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Ester stabilised carbanion (generic) more here |
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Ether (generic) more here |
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5-Ethyl-2-methyl pyridine more here |
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Ethylene oxide more here |
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Ethylene sulfide more here |
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Ethylenediaminetetraacetic acid tetraanion more here |
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Fluoride, organic (generic) more here |
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Fluoride ion more here |
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Fluorosulfonate ion more here |
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Formaldehyde more here |
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Formate ion more here |
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Formic acid more here |
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Fulminate ion more here |
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Germanate (dihydrogen) ion more here |
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Germanate (trihydrogen) ion more here |
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Germane anion (generic) more here |
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Germane hydride anion more here |
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Grignard reagent (generic) more here |
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Grignard reagent, alkyl magnesium bromide (generic) more here |
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Grignard reagent, alkyl magnesium chloride (generic) more here |
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Guanidine more here |
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6 Heterocycle (generic) more here |
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Heterocycle, polycyclic (generic) more here |
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Hydrazide anion more here |
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Hydrazine more here |
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Hydrazine, 1° alkyl (generic) more here |
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Hydrazine, alkyl (generic) more here |
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Hydrazine, N,N-Dialkyl (generic) more here |
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Hydrazone (generic) more here |
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Hydrogen acetylide anion more here |
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Hydrogen bromide more here |
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Hydrogen chloride more here |
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Hydrogen deuterium oxide more here |
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Hydrogen fluoride more here |
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Hydrogen iodide more here |
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Hydrogen peroxide more here |
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Hydrogen peroxide anion more here |
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Hydrogen phosphite ion more here |
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Hydrogen selenate ion more here |
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Hydrogen selenide more here |
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Hydrogen selenide ion more here |
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Hydrogen silicate ion more here |
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Hydrogen sulfate ion more here |
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Hydrogen sulfide more here |
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Hydrogen sulfide anion more here |
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Hydrogen sulfide, aqueous more here |
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Hydrogen telluride more here |
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Hydrogen telluride anion more here |
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Hydroxide ion more here |
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Hydroxy acid anion (generic) more here |
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beta-Hydroxy aldehyde (generic) more here |
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Hydroxylamine more here |
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Hypobromite ion more here |
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Hypochlorite ion more here |
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Hypoflourite ion more here |
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Hypoiodite ion more here |
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Hyponitrite ion more here |
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Hypophosphite ion more here |
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Imidazole more here |
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Imidazole anion more here |
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Imide ion more here |
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Imido anion (generic) more here |
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Imine, dialkyl (generic) more here |
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Imine, N-alkyl alkyl (generic) more here |
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Imine, trialkyl (generic) more here |
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Imino anion (generic) more here |
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Iodate ion more here |
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Iodide ion more here |
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Iodide, organic (generic) more here |
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Iodine dichloride ion more here |
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Isocyanate (generic) more here |
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Isocyanide (generic) more here |
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Isoquinoline more here |
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Isothiazole more here |
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Isothiocyanate (generic) more here |
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Ketal, cyclic (generic) more here |
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beta-Ketoaldehyde (generic) more here |
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beta-Ketoaldehyde anion (generic) more here |
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beta-Ketoester anion (generic) more here |
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beta-Ketoester (generic) more here |
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Ketone (generic) more here |
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Krypton more here |
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Lithium amide more here |
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Lithium carbide more here |
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Lithium enolate (generic) more here |
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Malonate diester (generic) more here |
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Malonic diester carbanion (generic) more here |
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Manganese(II) chloride more here |
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Methane thiol more here |
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Methanide ion more here |
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Methanol more here |
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Methoxide ion more here |
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N-Methyl aniline more here |
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Methyl anion more here |
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Methyl ester (generic) more here |
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Methyl ketone (generic) more here |
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Methyl ketone enolate ion (generic) more here |
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3-Methyl pyridine more here |
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4-Methyl pyridine more here |
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Methyl thiocarbanion (generic) more here |
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Methyl thioether (generic) more here |
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Methylamide anion more here |
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Methylamine more here |
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Methylthioanion more here |
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Neon more here |
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Nitranion (generic) more here |
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Nitrate ion more here |
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Nitride ion more here |
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Nitrile (generic) more here |
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Nitrite ion more here |
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Nitro compound (generic) more here |
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Nitroalkane alpha-carbanion (generic) more here |
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Nitrogen more here |
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Nitromethane more here |
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Nitrous acid more here |
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Nucleophile, anionic (generic) more here |
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Nucleophile, neutral (generic) more here |
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Tetrahydroorthoperiodate ion more here |
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Orthoperiodate (trihydrogen) ion more here |
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Orthosilicate ion more here |
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Oxalate dianion more here |
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Oxazole more here |
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Oxide ion more here |
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Oxime (generic) more here |
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Pentasulfide dianion more here |
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Perbromate ion more here |
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Perchlorate ion more here |
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Periodate ion more here |
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Permanganate ion more here |
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Peroxide anion, organic (generic) more here |
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Peroxide ion more here |
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Peroxide, organic (generic) more here |
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Phenol more here |
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Phenol (generic) more here |
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Phenoxide ion more here |
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Phenoxide ion (generic) more here |
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Phenyl amide anion more here |
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Phenyl anion more here |
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Phenyl anion (generic) more here |
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Phenyl azo (generic) more here |
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Phenyl ester (generic) more here |
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Phenyl ether (generic) more here |
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Phenyl phosphine anion more here |
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Phenyl silyl anion more here |
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Phenyl telluride more here |
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Phenylphosphine more here |
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Phenylselenide anion more here |
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Phenyltelluride anion more here |
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Phosphate di-substituted (generic) more here |
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Phosphate dianion, hydrogen more here |
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Phosphate ion more here |
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Phosphate, mono-substituted (generic) more here |
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Phosphide ion more here |
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Phosphine more here |
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Phosphine (generic) more here |
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Phosphine anion more here |
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Phosphine anion (generic) more here |
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Phosphite ion more here |
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Phosphonate stabilised carbanion (generic) more here |
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Phosphorus pentachloride more here |
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Phosphorus pentachloride g more here |
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Porphyrin more here |
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Potassium amide more here |
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Prop-2-en-1-imine more here |
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Purine more here |
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Pyrazine more here |
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Pyrazole more here |
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Pyridazine more here |
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Pyridine more here |
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Pyridine (generic) more here |
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Pyrimidine more here |
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Quinoline more here |
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Selenate ion more here |
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Selenide anion (generic) more here |
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Selenide ion more here |
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Selenite (hydrogen) ion more here |
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Selenite ion more here |
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Selenoether (generic) more here |
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Selinophenol more here |
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Silicate ion more here |
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Silyl anion more here |
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Silyl anion (generic) more here |
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Steam more here |
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Stibine more here |
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Stibine anion more here |
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Stibnide ion more here |
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Succinimide anion more here |
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Sulfate ion more here |
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Sulfide ion more here |
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Sulfinate anion (generic) more here |
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Sulfite ion more here |
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Sulfoxide (generic) more here |
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Superoxide ion more here |
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Tartrate dianion more here |
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Telluride (generic) more here |
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Telluride anion (generic) more here |
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Tellurite (hydrogen) ion more here |
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Tellurite ion more here |
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Tellurium dianion more here |
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Telluroether (generic) more here |
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Tetrafluoromethane more here |
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Tetrahydrofuran more here |
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1,1,3,3-Tetramethyl guanidine more here |
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N,N,N, N-Tetramethylethylene diamine more here |
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Tetrasulfide dianion more here |
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Tetrathionate ion more here |
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Thiazole more here |
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Thioacetal (generic) more here |
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Thioacetal, cyclic (generic) more here |
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Thioanion (generic) more here |
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Thiocyanate ion more here |
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Thioether (generic) more here |
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Thioketal, cyclic (generic) more here |
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Thioketone (generic) more here |
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Thiol (generic) more here |
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Thiophenol more here |
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Thiophenoxide ion more here |
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Thiosulfate ion more here |
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Thiourea more here |
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1,3,5-Triazine more here |
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Tricyanomethane anion more here |
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Triethylphosphate more here |
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Trifluoromethane sulfonate ion more here |
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Triiodide ion more here |
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Trimethylamine more here |
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Trimethylphosphite more here |
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Triphenylmethyl anion more here |
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Triphenylphosphine more here |
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Trisulfide dianion more here |
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Tungstate ion more here |
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Urea more here |
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Urea or carbonate (generic) more here |
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Vinyl anion more here |
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Vinyl ether (generic) more here |
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Water more here |
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Wittig reagent (generic) more here |
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Xenon more here |
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Ylid (generic) more here |
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Poster | Nucleophiles & Bases |
© Mark R. Leach 1999 –
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