Lewis Acid/Base Interaction Matrix Database

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:

  • Proton abstracting Brønsted bases
  • Ligands around metal complex ions
  • Attacking nucleophiles
  • Nucleofugal leaving groups
  • Non-interfering spectator anions
  • Co-complexing or solvating agents

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:

  • Carbanion centres: H3C, enolates, etc., are of huge importance in organic chemistry because the carbanion can act as a nucleophile at a carbon-nulceofuge centre, C-Nfg, such as an alkyl bromide or tosylate. Thje effect is to increase the length of the carbon skeleton.

    The rule is that π-stabilisation makes a carbanion centre less basic but more nucleophilic, as discussed in more detail elsewhere in this chemogenesis webbook, here.

  • α-Effect ("alpha effect") bases like hydrazine and hydrogen peroxide are rendered more basic & more nucleophilic by an adjacent lone-pair of electrons. Find α-effect ("alpha effect") Lewis bases in The Chemical Thesaurus.

  • Bidentate and polydentate bases have two or more similar Lewis base centres and are commonly enployed as ligands in transition metal chemistry. Find bidentate and polydentate bases in The Chemical Thesaurus.

  • Ambident (ambidentate) bases have two dissimilar Lewis base centres and show selectivity. Find ambident and polydentate bases in The Chemical Thesaurus.

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 superacids 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)
Acetal (generic)

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Acetal, cyclic (generic)

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Acetaldehyde enolate

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Acetate ester (generic)

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Acetate ion

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Acetylide anion (generic)

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Acrylate ion

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Alcohol (generic)

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1° Alcohol (generic)

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1° Alcohol, R-CH2CH2OH (generic)

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2° Alcohol (generic)

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2° Alcohol, cyclohexyl (generic)

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3° Alcohol (generic)

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Aldehyde (generic)

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Aldehyde stabilised carbanion (generic)

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Aldehyde, alpha-hydrogen (generic)

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Alkenyl lithium (generic)

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Alkoxide (generic)

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1° Alkoxide ion (generic)

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2° Alkoxide ion (generic)

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3° Alkoxide ion (generic)

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3-Alkoxy propanoate, alkyl (generic)

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Alkyl bromide (generic)

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Alkyl chloride (generic)

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Alkyl lithium (generic)

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Alkyl nitrile alpha-carbanion (generic)

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Allyl alkoxide ion

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1° Allylic alcohol (generic)

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2° Allylic alcohol (generic)

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1° Amide (generic)

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1° Amide, anion (generic)

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2° Amide (generic)

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3° Amide (generic)

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Amide ion

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Amidosulfate anion

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1° Amine (generic)

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1° Amine, 1° alkyl (generic)

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2° Amine (generic)

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2 Amine, (RCH2)2NH (generic)

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2° Amine, R, R- (generic)

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3° Amine (generic)

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3° Amine, (RCH2)3N (generic)

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Ammonia

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Ammonia 0.880

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Ammonia, aqueous

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Aniline

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Aniline, N-2° alkyl (generic)

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Aniline, N-alkyl (generic)

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Anionic Lobe-HOMO Lewis base congeneric planar

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Anisole

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Aqueous alkali, 0.05 to 1.0 molar (generic)

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Argon

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Arsenate (dihydrogen) ion

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Arsenate (hydrogen) ion

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Arsenide ion

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Arsenite ion

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Arsinate ion

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Arsine

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Arsine anion

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Arsine anion (generic)

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Arsine, trialkyl (generic)

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Azide ion

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Aziridine

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Base, charged (generic)

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Base, neutral (generic)

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Benzoate ion

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Benzoic acid

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Benzyl alcohol (generic)

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Benzyl anion

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Benzyl anion (generic)

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Bicarbonate ion

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Bisulfite ion

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Borate ion

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Brønsted acid, hydroxy (generic)

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Bromate ion

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Bromide ion

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2-Butanol

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tertiary Butanol

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tertiary Butyl alkoxide

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tertiary Butyl carbanion

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Carbanion (generic)

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1° Carbanion (generic)

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2° Carbanion (generic)

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3° Carbanion (generic)

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Carbanion, stabilised (generic)

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Carbide ion

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Carboiimide (generic)

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Carbon dioxide

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Carbon monoxide

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Carbonate diester (generic)

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Carbonate ion

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Carbonyl function (generic)

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Carboxylate dianion (generic)

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Carboxylate ion (generic)

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Carboxylic acid (generic)

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Chlorate ion

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Chloride ion

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Chlorine diiodide ion

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Chlorite ion

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beta-Chloroethyl amine (generic)

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beta-Chloroethyl ether (generic)

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beta-Chloroethyl thioether (generic)

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Chromate ion, hydrogen

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Chromate(VI) ion

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18-Crown-6

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Cumulene (generic)

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Cyanamide ion

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Cyanate ion

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Cyanide ion

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Cyanohydrin, alkyl (generic)

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Cyclopropane carboxylate ion

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Cyclopropenyl anion

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Cyclopropyl anion

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Deuterium oxide

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Dialkyl arsine (generic)

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Dichromate(VI) ion

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Diglyme

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Dihydrogen phosphate ion

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beta-Diketone anion (generic)

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beta-Diketone (generic)

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Dimethyl ether

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Dimethylamide anion

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Dimethylamine

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N,N-Dimethyl aniline

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Dimethylsulfoxide

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Dimethylsulfoxide anion

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Dimethylthioether

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trans 1,2-Diol (generic)

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Diphenyl amide anion

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Diphenyl ether

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Diphenylamine

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Diphenylmethyl anion

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Disulfide (hydrogen) ion

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Disulfide anion, organic (generic)

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Disulfide dianion

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Disulfide, organic (generic)

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Disulfite ion

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1,3-Dithiane anion (generic)

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1,2-Dithioethane dianion

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Dithionate ion

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Dithionite ion

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Enamine anion (generic)

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Enolate anion (generic)

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Epoxide (generic)

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Ester (generic)

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Ester stabilised carbanion (generic)

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Ether (generic)

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5-Ethyl-2-methyl pyridine

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Ethylene oxide

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Ethylene sulfide

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Ethylenediaminetetraacetic acid tetraanion

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Fluoride, organic (generic)

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Fluoride ion

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Fluorosulfonate ion

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Formaldehyde

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Formate ion

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Formic acid

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Fulminate ion

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Germanate (dihydrogen) ion

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Germanate (trihydrogen) ion

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Germane anion (generic)

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Germane hydride anion

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Grignard reagent (generic)

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Grignard reagent, alkyl magnesium bromide (generic)

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Grignard reagent, alkyl magnesium chloride (generic)

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Guanidine

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6 Heterocycle (generic)

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Heterocycle, polycyclic (generic)

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Hydrazide anion

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Hydrazine

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Hydrazine, 1° alkyl (generic)

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Hydrazine, alkyl (generic)

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Hydrazine, N,N-Dialkyl (generic)

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Hydrazone (generic)

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Hydrogen acetylide anion

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Hydrogen bromide

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Hydrogen chloride

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Hydrogen deuterium oxide

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Hydrogen fluoride

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Hydrogen iodide

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Hydrogen peroxide

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Hydrogen peroxide anion

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Hydrogen phosphite ion

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Hydrogen selenate ion

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Hydrogen selenide

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Hydrogen selenide ion

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Hydrogen silicate ion

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Hydrogen sulfate ion

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Hydrogen sulfide

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Hydrogen sulfide anion

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Hydrogen sulfide, aqueous

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Hydrogen telluride

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Hydrogen telluride anion

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Hydroxide ion

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Hydroxy acid anion (generic)

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beta-Hydroxy aldehyde (generic)

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Hydroxylamine

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Hypobromite ion

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Hypochlorite ion

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Hypoflourite ion

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Hypoiodite ion

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Hyponitrite ion

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Hypophosphite ion

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Imidazole

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Imidazole anion

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Imide ion

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Imido anion (generic)

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Imine, dialkyl (generic)

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Imine, N-alkyl alkyl (generic)

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Imine, trialkyl (generic)

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Imino anion (generic)

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Iodate ion

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Iodide ion

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Iodide, organic (generic)

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Iodine dichloride ion

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Isocyanate (generic)

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Isocyanide (generic)

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Isoquinoline

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Isothiazole

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Isothiocyanate (generic)

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Ketal, cyclic (generic)

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beta-Ketoaldehyde (generic)

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beta-Ketoaldehyde anion (generic)

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beta-Ketoester anion (generic)

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beta-Ketoester (generic)

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Ketone (generic)

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Krypton

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Lithium amide

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Lithium carbide

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Lithium enolate (generic)

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Malonate diester (generic)

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Malonic diester carbanion (generic)

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Manganese(II) chloride

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Methane thiol

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Methanide ion

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Methanol

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Methoxide ion

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N-Methyl aniline

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Methyl anion

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Methyl ester (generic)

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Methyl ketone (generic)

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Methyl ketone enolate ion (generic)

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3-Methyl pyridine

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4-Methyl pyridine

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Methyl thiocarbanion (generic)

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Methyl thioether (generic)

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Methylamide anion

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Methylamine

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Methylthioanion

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Neon

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Nitranion (generic)

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Nitrate ion

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Nitride ion

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Nitrile (generic)

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Nitrite ion

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Nitro compound (generic)

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Nitroalkane alpha-carbanion (generic)

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Nitrogen

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Nitromethane

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Nitrous acid

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Nucleophile, anionic (generic)

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Nucleophile, neutral (generic)

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Tetrahydroorthoperiodate ion

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Orthoperiodate (trihydrogen) ion

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Orthosilicate ion

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Oxalate dianion

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Oxazole

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Oxide ion

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Oxime (generic)

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Pentasulfide dianion

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Perbromate ion

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Perchlorate ion

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Periodate ion

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Permanganate ion

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Peroxide anion, organic (generic)

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Peroxide ion

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Peroxide, organic (generic)

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Phenol

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Phenol (generic)

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Phenoxide ion

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Phenoxide ion (generic)

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Phenyl amide anion

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Phenyl anion

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Phenyl anion (generic)

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Phenyl azo (generic)

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Phenyl ester (generic)

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Phenyl ether (generic)

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Phenyl phosphine anion

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Phenyl silyl anion

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Phenyl telluride

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Phenylphosphine

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Phenylselenide anion

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Phenyltelluride anion

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Phosphate di-substituted (generic)

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Phosphate dianion, hydrogen

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Phosphate ion

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Phosphate, mono-substituted (generic)

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Phosphide ion

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Phosphine

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Phosphine (generic)

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Phosphine anion

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Phosphine anion (generic)

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Phosphite ion

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Phosphonate stabilised carbanion (generic)

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Phosphorus pentachloride

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Phosphorus pentachloride g

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Porphyrin

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Potassium amide

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Prop-2-en-1-imine

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Purine

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Pyrazine

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Pyrazole

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Pyridazine

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Pyridine

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Pyridine (generic)

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Pyrimidine

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Quinoline

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Selenate ion

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Selenide anion (generic)

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Selenide ion

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Selenite (hydrogen) ion

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Selenite ion

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Selenoether (generic)

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Selinophenol

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Silicate ion

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Silyl anion

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Silyl anion (generic)

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Steam

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Stibine

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Stibine anion

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Stibnide ion

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Succinimide anion

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Sulfate ion

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Sulfide ion

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Sulfinate anion (generic)

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Sulfite ion

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Sulfoxide (generic)

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Superoxide ion

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Tartrate dianion

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Telluride (generic)

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Telluride anion (generic)

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Tellurite (hydrogen) ion

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Tellurite ion

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Tellurium dianion

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Telluroether (generic)

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Tetrafluoromethane

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Tetrahydrofuran

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1,1,3,3-Tetramethyl guanidine

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N,N,N, N-Tetramethylethylene diamine

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Tetrasulfide dianion

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Tetrathionate ion

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Thiazole

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Thioacetal (generic)

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Thioacetal, cyclic (generic)

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Thioanion (generic)

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Thiocyanate ion

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Thioether (generic)

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Thioketal, cyclic (generic)

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Thioketone (generic)

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Thiol (generic)

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Thiophenol

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Thiophenoxide ion

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Thiosulfate ion

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Thiourea

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1,3,5-Triazine

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Tricyanomethane anion

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Triethylphosphate

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Trifluoromethane sulfonate ion

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Triiodide ion

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Trimethylamine

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Trimethylphosphite

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Triphenylmethyl anion

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Triphenylphosphine

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Trisulfide dianion

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Tungstate ion

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Urea

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Urea or carbonate (generic)

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Vinyl anion

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Vinyl ether (generic)

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Water

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Wittig reagent (generic)

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Xenon

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Ylid (generic)

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Poster
Nucleophiles & Bases

© Mark R. Leach 1999-


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