Alcohols and phenols

Naming alcohols and phenols

However, phenol is sufficiently acidic for it to have recognizably acidic properties - even if it is still a very weak acid. We review the physical properties of these compounds, and discuss methods used to obtain the lower members of the series on an industrial scale. An example is the reaction of methanol with hydrogen bromide to give methyloxonium bromide, which is analogous to the formation of hydroxonium bromide with hydrogen bromide and water: Acidity of Phenol Compounds like alcohols and phenol which contain an -OH group attached to a hydrocarbon are very weak acids. They do this by polarization of their bonding electrons, and the bigger the group, the more polarizable it is. The mixture left in the tube will contain sodium phenoxide. Energy is required for both of these processes. In place of those original hydrogen bonds are merely van der Waals dispersion forces between the water and the hydrocarbon "tails. In this method of naming, the longest continuous alkyl chain forms the stem of the ether name and the alkoxy group is named as a substituent on the alkane backbone. Alcohols: Rules for naming alcohols follow the guidelines already given for alkanes, in summary The number of carbon atoms in the longest carbon chain containing the OH group gives the stem Use a prefix to identify the position of the carbon carrying the OH and a suffix of -ol.

The discussion begins with an outline of the nomenclature of alcohols and phenols. That is why phenol is only a very weak acid. We also introduce the concept of protecting a sensitive functional group during an organic synthesis.

acidity of alcohols and phenols

However, phenol is sufficiently acidic for it to have recognizably acidic properties - even if it is still a very weak acid. This means that many of the original hydrogen bonds being broken are never replaced by new ones.

nomenclature of phenols

To answer this question we must evaluate the manner in which an oxygen substituent interacts with the benzene ring. Alcohols can undergo a wide variety of reactions, and because of this reactivity and because they can be prepared in a number of different ways, alcohols occupy an important position in organic chemistry.

Supporting evidence that the phenolate negative charge is delocalized on the ortho and para carbons of the benzene ring comes from the influence of electron-withdrawing substituents at those sites.

Properties of alcohols and phenols

At four carbon atoms and beyond, the decrease in solubility is noticeable; a two-layered substance may appear in a test tube when the two are mixed. Alcohols can undergo a wide variety of reactions, and because of this reactivity and because they can be prepared in a number of different ways, alcohols occupy an important position in organic chemistry. As the length of the alcohol increases, this situation becomes more pronounced, and thus the solubility decreases. This the main reason for higher boiling points in alcohols. Phenol can lose a hydrogen ion because the phenoxide ion formed is stabilised to some extent. Spreading the charge around makes the ion more stable than it would be if all the charge remained on the oxygen. Even allowing for the increase in disorder, the process becomes less feasible. In the case of alcohols, hydrogen bonds occur between the partially-positive hydrogen atoms and lone pairs on oxygen atoms of other molecules. The discussion begins with an outline of the nomenclature of alcohols and phenols. For example, in solution in water: Phenol is a very weak acid and the position of equilibrium lies well to the left. In this method of naming, the longest continuous alkyl chain forms the stem of the ether name and the alkoxy group is named as a substituent on the alkane backbone. The effect of van der Waals forces Boiling points of the alcohols: Hydrogen bonding is not the only intermolecular force alcohols experience. Both of these increase the size of the van der Waals dispersion forces, and subsequently the boiling point. There is some fizzing as hydrogen gas is given off.

The energy released when these new hydrogen bonds form approximately compensates for the energy needed to break the original interactions. The conjugate bases of simple alcohols are not stabilized by charge delocalization, so the acidity of these compounds is similar to that of water.

Structures of alcohols and phenols

That is why phenol is only a very weak acid. Chemical Reactions of Alcohols involving the O-H bond of Compounds with Basic Properties Alcohols are bases similar in strength to water and accept protons from strong acids. These attractions get stronger as the molecules get longer and have more electrons. As the length of the alcohol increases, this situation becomes more pronounced, and thus the solubility decreases. Phenol can lose a hydrogen ion because the phenoxide ion formed is stabilised to some extent. Compare ethane and ethanol: Ethanol is a longer molecule, and the oxygen atom brings with it an extra 8 electrons. In addition, there is an increase in the disorder of the system, an increase in entropy. An energy diagram showing the effect of resonance on cyclohexanol and phenol acidities is shown on the right. Comparison between alkanes and alcohols: Even without any hydrogen bonding or dipole-dipole interactions, the boiling point of the alcohol would be higher than the corresponding alkane with the same number of carbon atoms. Phenol is warmed in a dry tube until it is molten, and a small piece of sodium added. However, phenol is sufficiently acidic for it to have recognizably acidic properties - even if it is still a very weak acid.

The -OH ends of the alcohol molecules can form new hydrogen bonds with water molecules, but the hydrocarbon "tail" does not form hydrogen bonds. Comparison between alkanes and alcohols: Even without any hydrogen bonding or dipole-dipole interactions, the boiling point of the alcohol would be higher than the corresponding alkane with the same number of carbon atoms.

The resonance stabilization in these two cases is very different. Alcohols are so weakly acidic that, for normal lab purposes, their acidity can be virtually ignored. These attractions get stronger as the molecules get longer and have more electrons. A similar set of resonance structures for the phenolate anion conjugate base appears below the phenol structures. The hydrogen bonding and dipole-dipole interactions are much the same for all alcohols, but dispersion forces increase as the alcohols get bigger. This increases the sizes of the temporary dipoles formed. Since the resonance stabilization of the phenolate conjugate base is much greater than the stabilization of phenol itself, the acidity of phenol relative to cyclohexanol is increased. In place of those original hydrogen bonds are merely van der Waals dispersion forces between the water and the hydrocarbon "tails. Consider ethanol as a typical small alcohol. Boiling Points The chart below shows the boiling points of the following simple primary alcohols with up to 4 carbon atoms: These boiling points are compared with those of the equivalent alkanes methane to butane with the same number of carbon atoms. In alkanes, the only intermolecular forces are van der Waals dispersion forces. Solubility of alcohols in water Small alcohols are completely soluble in water; mixing the two in any proportion generates a single solution.

In alkanes, the only intermolecular forces are van der Waals dispersion forces. In addition, there is an increase in the disorder of the system, an increase in entropy.

This phenolic acidity is further enhanced by electron-withdrawing substituents ortho and para to the hydroxyl group, as displayed in the following diagram.

phenol functional group
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Alcohols and phenols questions (practice)