Methanoate anion

There is extremely effective delocalisation, with consequent stabilisation, in the methanoate anion involving as it does two canonical structures of identical energy, and though delocalisation can take... 

We should thus expect the equilibrium to be shifted to the left compared with that for methanoic acid/methanoate anion, and it is in fact found that the pKa of ethanoic acid is 4-76, compared with 3-77 for methanoic acid. However, the degree of structural change effected in so small a molecule as methanoic acid by replacement of H by CH3 makes it doubtful whether so simple an argument is really valid it could well be that the relative solvation possibilities in the two cases are markedly affected by the considerably different shapes of, as well as by the relative charge distribution in, the two small molecules. 

The chemical structures of I and VI reveal the strong similarities between ethanoic and methanoic acids, yet the smaller molecule is considerably nastier to the skin. Why Methanoic acid dissociates in water to form the solvated methanoate anion HCOO-(aq) and a solvated proton in a directly analogous fashion to ethanoic acid dissolving in water Equation (6.1). In methanoic acid of concentration 0.01 mol dm-3, about 0.14 per cent of the molecules have dissociated to yield a solvated proton. By contrast, in ethanoic acid of the same concentration, only 0.04 per cent of the molecules have dissociated. We say the methanoic acid is a stronger acid than ethanoic since it yields more protons per mole. Conversely, ethanoic acid is weaker. 

A similar situation exists for the anion that results when a carboxylic acid such as methanoic acid ionizes. The product is a resonance-stabilized methanoate anion. (The anion is called a carboxylate anion.) The two structures, shown below, contribute equally to the resonance hybrid. 

Attack at the carbonyl group with formation of the intense green-yellow fluorescent anion 188a R = CH(CH3)2 occurs, for example, if sodium methano-late in benzene/methanol is used. In contrast, methyl magnesium bromide in... 

M14 anions were characterized by carbonation when the Mi4-methanoic acids formed were sufficiently stable8. The stereochemistry of this reaction was determined as retention (Scheme 28)169 170. 

Anion exchange reactions, in thiopyrylium salts and congeners, 60, 123-4 (lOJAnnulene, 3-t-butoxy-1,6-methano-, condensation with 3-diazopyrazoles, 59, 74... 

The Cannizzaro reactionof non-enolizable aldehydes is another example of a hydride transfer reaction. It is carried out under alkaline conditions and involves not only the addition of a hydroxide ion to one aldehyde but the stabilization of the resultant acid as the anion (Scheme 3.41). Methanal (formaldehyde), which gives methanoic acid (formic acid), a relatively strong carboxylic acid, makes a good hydrogen donor in a cross-Cannizzaro reaction. 

From the coupling constants of CH2 protons, it is concluded that the cation 65 + exists in the methano-bridged from 66 of the neutral 64, whereas the anion 65 adopts the bisnorcaradiene form 67 of the dianion 65. ... 

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