Alcohols atomic charges

Both NaH and KH are used to deprotonate alcohols. KH is more reactive than NaH. Compare atomic charges and electrostatic potential maps of potassium hydride and sodium hydride. For which is the hydrogen more negatively charged Which should be the better source of hydride ... 

FIGURE 3.2 Examples of calculated partial atomic charges, (a) Picolinic acid (b) Isopropyl alcohol. 

In this study, it was observed that only the atomic charges of nitrogen, oxygen, and polar hydrogen contribute signiLcantly to the solubility in isopropyl alcohol. A polar hydrogen is empirically deLned... 

The issue of transferability of atomic charge models between conformations has been more vigorously discussed in the last decade. Most force fields assume that the charge distribution associated with each atom is independent of conformation. However, it has been noted that potential derived atomic charges do vary with the conformation of the molecule used to derive them and that these variations have a significant effect on computed properties such as the free energy of hydration of alcohols. 

Zhang, J., Meinoder, T. and Gasteiger, J. (2006) Prediction of pJQ values for aliphatic carboxylic acids and alcohols with empirical atomic charge descriptors. /. Chem. Inf. Model., 46, 2256-2266. 

In 1993 Dixon and Jurs [209] used empirically calculated atomic charges to describe the pK s of a diverse collection of alcohols, phenols, and carboxylic acids. They found a strong linear relationship (r = 0.993) between their charge parameters and the pK s for a set of 135 oxyacids. Citra later used charges and bond orders from AMI calculations to characterize the pK s of phraiols, carboxylic acids, and alcohols [210]. Here too the best correlations were found for the phenols. Citra also compared his MLR results with results from two commercially available programs and found that all three approaches performed well. He cautioned, however, that his molecular orbital results were sensitive to the final optimized geometry found in the calculations. 

Molecular charge distributions of the solute molecules were represented aS sets of partial charges centered on the nuclei. For methanol, the ESP charges were used [26]. For the other three alcohol molecules and the anesthetics, the charges were fitted to reproduce the quantum-mechan-ically computed electrostatic potentials around the molecules. For flexible solutes, a multi-conformational fit of the atomic charges was carried out, whereby these... 

Phenol condenses with phthahc anhydride in the presence of concentrated sulphuric acid or anhydrous zinc chloride to yield the colourless phenolphthalein as the main product. When dilute caustic alkah is added to an alcoholic solution of phenolphthalein, an intense red colouration is produced. The alkali opens the lactone ring in phenolphthalein and forms a salt at one phenolic group. The reaction may be represented in steps, with the formation of a h3q)othetical unstable Intermediate that changes to a coloured ion. The colour is probably due to resonance which places the negative charge on either of the two equivalent oxygen atoms. With excess of concentrated caustic alkali, the first red colour disappears this is due to the production of the carbinol and attendant salt formation, rendering resonance impossible. The various reactions may be represented as follows ... 

Neutral Lewis bases such as water alcohols and carboxylic acids are much weaker nucleophiles than their conjugate bases When comparing species that have the same nucleophilic atom a negatively charged nucleophile is more reactive than a neutral one... 

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