Acetic acid electron density

The most striking property of water is that its solid form is less dense than its liquid form ice floats at the surface of liquid water (Figure 6.8). With a few exceptions, (for example, silicon, gallium, germanium, bismuth, and pure acetic acid), the density of almost all other substances is greater in the solid state than in the liquid state. To understand why water is different, we have to examine the electronic structure of the H2O molecule. As we saw in Chapters 2 and 3, there are two pairs of nonbonding electrons, or two lone pairs, on the oxygen atom ... 

C17-0091. Acetic acid (CH3 CO2 H) is weaker than chloroacetic acid (CICH2 CO2 H). Draw Lewis structures of these two acids. Draw an arrow indicating the effect of the Cl atom on the electron density in the rest of the molecule, and use this drawing to explain why chloroacetic acid is the stronger acid. 

Fig. 32. Packing relations and steric fit of the 26 acetic acid (1 1) clathrate (isomorphous with the corresponding propionic acid clathrate of 26)1U- (a) Stereoscopic packing illustration acetic acid (shown in stick style) forms dimers in the tunnel running along the c crystal axis of the 26 host matrix (space filling representation, O atoms shaded), (b) Electron density contours in the plane of the acetic acid dimer sa First contour (solid line) is at 0.4 eA" while subsequent ones are with arbitrary spacings of either 0.5 and 1 eA 3. Density of the enclosing walls comes from C and H atoms of host molecules.

Vanadium(n) Complexes.—Dehydration of VSO. THjO has been shown to proceed via the formation of VS04,mH20 (where n = 6, 4, or 1) and V(OH)-(SO4), which were characterized by X-ray studies. The polarographic behaviour and the oxidation potential of the V -l,2-cyclohexanediamine-tetra-acetic acid complex, at pH 6—12, have been determined.Formation constants and electronic spectra have been reported for the [Vlphen),] " and [V20(phen)] complexes. The absorption spectrum of V ions doped in cadmium telluride has been presented and interpreted on a crystal-field model. The unpaired spin density in fluorine 2pit-orbitals of [VF ] , arising from covalent transfer and overlap with vanadium orbitals, has been determined by ENDOR spectroscopy and interpreted using a covalent model. " ... 

Although successfully carried out with model compounds, the cyclopentyl i dene acetal here could not be hydrolyzed selectively in the presence of the other protecting groups. Selective deprotection occurred only upon addition of trinitrotoluene, which us a more electron-deficient aromalic system forms a charge-transfer complex with the electron rich aromalic portion of the PMPh acetal. The charge-transfer complex decreases the electron density of the acetal and thus increases its stability, presumably due to reduced stabilization of cation 38 In this way it proved possible to release the alcohol functions at C-12 and C-13 selectively with acid. 

The result of this inductive effect is that the electron density on the carboxylate anion is reduced, the negative charge is distributed over more atoms, and the chloroacetate anion is stabilized relative to acetate. Because the chloroacetate anion is more stable than the acetate ion, its conjugate acid, chloroacetic acid, is a stronger acid than the conjugate acid of the acetate ion, acetic acid (Table 3.1). 

The available spectral and calculated (Pariser-Parr-Pople method) data constitute evidence for a decrease in electron density in the benzene ring and activation of the 5-position to electrophilic attack in the 4-hydroxythiazinone (203) (79KGS44). Nitration was carried out in organic solvents at -60°C. The best results were obtained in the case of nitration with nitric acid (specific gravity = 1.42) in glacial acetic acid containing catalytic amounts of acetic anhydride at 40-50C (Scheme 93). The mono-... 

The cobalt (III) complex, (1,2-C2B9Hn)2Co, undergoes bromination in glacial acetic acid solution to afford a hexabromo derivative, (1,2-C2B9HsBr3) 2Co 54). An X-ray crystallographic study of this product 14) showed that bromination occurred on the boron atoms farthest from the polyhedral carbon atoms, those boron atoms expected to have the greatest electron density, as predicted for an electrophilic attack mechanism. 

Since sulfonation of pyridine iV-oxide is about as difficult as is that of pyridine itself and takes place at the 3-position,17 it has been assumed18 that, in fuming sulfuric acid, pyridine iV-oxide reacts only in the salt form (3), when the prediction is that substitution at C-3 would take place. It is, however, difficult to account for the fact that bromination, even at 110° in the presence of iron powder, does not occur.17 Bromination in chloroform solution in the presence of acetic anhydride and sodium acetate (when the O-acetate is the the probable substrate) take place readily, however, to give 3,5-dibromopyridine JV-oxide.19 The predicted order of nucleophilic reactivity, on the basis of both atom localization energies and ground-state v-electron density calculations, is 4 > 2 > 3. The same order is predicted for the nucleophilic substitution reactions of the salts of pyridine JV-oxide. In actual practice, iV-alkoxypyridinium derivatives undergo nucleophilic attack preferentially at C-2.20-23 The reaction of some pyridine iV-oxides with phosphorus pentachloride may involve the formation... 

Due to the low electron density at the carbon atoms in 1,3,4-thiadiazole, such reactions as nitration, sulfonation, acetylation, halogenation, etc. normally do not take place. However, 2-amino-substituted 1,3,4-thiadiazoles (73a-i) react with bromine in acetic acid to give the 5-bromo derivatives (74a-i). Similarly, the thiadiazolines (75b) and (75d-f) yield the corresponding 5-bromo derivatives (76b) and (76d-f). The thiadiazoline (75a), however,... 

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