What are nomenclature for monohydric alcohols


Alcohols are hydrocarbons with a functional group. In an alkane, hydrogen atoms are replaced by hydroxyl groups (-OH), which is why alcohols generally have the following structure:

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Classification of alcohols

Alcohols can be classified based on the number of hydroxyl groups bound in the molecule. In the case of alcohols with a hydroxyl group, it is one monovalent Alcohol, in the case of alcohols with two hydroxyl groups around one bivalent and in the case of alcohols with three hydroxyl groups by one trihydric alcohol. In the case of polyhydric alcohols, only one hydroxyl group is usually bonded to a carbon atom, since otherwise they are usually unstable and disintegrate with elimination of water.

      • Alcohols can also be classified according to the position of the hydroxyl group in the molecule. There are the following options:
      • The hydroxy group is on primary Carbon atom attached to primary alcohol
      • The hydroxy group is on secondary Carbon atom attached to secondary alcohol
      • The hydroxy group is on tertiary Carbon atom bound tertiary alcohol

But what are primary, secondary and tertiary carbon atoms?
These designations indicate how many more carbon atoms are bonded to a carbon atom. Accordingly, another is bound to a primary carbon atom, two more to a secondary one and three more to a tertiary one. The following are examples of the various alcohols that result from this:

Melting and boiling points of alcohols

As already described for the alkanes, the melting and boiling points depend on the intermolecular interactions. The same decision-making rules apply here with regard to the van der Waals interactions as for the hydrocarbons. In the case of alcohols, in addition to the van der Waals interactions, there are also hydrogen bonds between a free electron pair on the oxygen atom of the hydroxyl group and a hydrogen atom of another hydroxyl group. The free electron pair, however, cannot form a hydrogen bond with the hydrogen atoms that are bound to carbon atoms, since these are not sufficiently positively polarized due to the small electronegativity difference.

Compared to hydrocarbons, alcohols have higher melting and boiling points because, due to the strong hydrogen bonds, the intermolecular interactions that have to be overcome for melting or boiling are significantly higher.
If two different alcohols are compared with one another, the melting and boiling points increase with the number of hydroxyl groups, since more hydrogen bonds can then be formed.

Solubility of alcohols

In order to be able to make a statement about the solubility of alcohols, one has to consider the polarity of the molecule. The hydroxyl group in alcohol is polar, whereas the hydrocarbon chain is non-polar. The larger the hydrocarbon chain, the larger the non-polar part of the molecule and the better the molecule dissolves in non-polar solvents such as gasoline. The shorter the hydrocarbon chain, the smaller the non-polar part of the molecule and it dissolves increasingly better in polar solvents such as water. Experimentally, it can be established that alcohols up to propanol dissolve well in water.

Reaction behavior of alcohols

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Deprotonation of the hydroxyl group

Alcohols can react like a Brönsted acid (proton donor), so the hydroxyl group can donate a proton.

However, alcohols are very weak acids and therefore do not particularly like to give up their protons. The longer the hydrocarbon chain of an alcohol, the more difficult it is for the proton to be released. This is due to the + I effect of the hydrocarbon chain. The longer the chain, the stronger the electron-donating + I effect and the higher the electron density on the hydroxyl group. As a result, the proton is more strongly attracted and less emitted.

Condensation reaction (nucleophilic substitution)

Alcohols can react with a carboxylic acid to form an ester in a so-called condensation reaction. This creates water.


Some alcohols can also react with an oxidizing agent under oxidation. The position of the hydroxyl group plays a decisive role:
Primary alcohols can be oxidized to aldehydes.

Secondary Alcohols allow themselves Ketones oxidize.
Example: propan-2-ol to propanone

Tertiary alcohols cannot be easily oxidized.
Example: 2-methylpropan-2-ol

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