What are analog series and homologous series



 

As Alkanols In organic chemistry, one describes a group of substances that is derived from alkanes (saturated hydrocarbons). All alkanols have one or more hydroxyl group (s) as a functional group. Analogous compounds derived from unsaturated hydrocarbons are called alkenols (with one or more double bonds) and alkynols (with one or more triple bonds). The word Alkanols comes from the IUPAC nomenclature.

The terms alcohol and Alkanol are not synonymous. The term alcohol relates to the functionality of the hydroxyl group, while the term alkanol also defines the saturated character of the alkyl radical.

Valence of the alkanols

If there is more than one hydroxyl group in an alcohol molecule, their number is indicated by adding a Greek syllable (-di, -tri-, etc.) corresponding to the number of hydroxyl groups in front of the ending -ol and we speak of polyhydric alkanols. An alkanediol is the glycol (1,2-ethanediol), an alkanetriol the glycerine (1,2,3-propanetriol). The number in front of the name of the alkyl radical indicates the position of the functional group (s). This also applies to monohydric alkanols, e.g. B. 2-propanol (common name isopropanol).

properties

The most important common characteristic of the alkanols is their hydrophilicity. This property decreases with increasing length of the alkyl radical and increases with the number of hydroxyl groups. The short-chain alkanols in particular are often used as solvents due to their amphiphilic character.

Homologous series

The homologous series of n-Alcanols is (up to C10):

The general formula of monohydric alkanols is C.nH2n + 1OH

proof

Most detection reactions are based on the oxidation of the alkanols to aldehydes, ketones and carboxylic acids.

Alcotest

Alkanols react with (yellow-orange) dichromate ions in a strong sulfuric acid solution to green chromium (III) and oxidation products (Alcotest):

Certest

A concentrated (yellow) solution of cerium (IV) ammonium nitrate is mixed with a dilute solution of the unknown substance. The presence of alkanols causes a color change to red (sometimes also green). The reason is a complex formation (ligand substitution) in which an alcohol / phenol coordinates with the oxygen atom on cerium (IV) to form a red / green / brown complex.

Lucas reagent

The Lucas reagent allows you to differentiate between primary, secondary and tertiary alkanols. The hydroxyl group is replaced with a chlorine atom via a nucleophilic substitution. The result is the formation of a water-insoluble substance that is deposited. The speed of this phase formation determines the type of alkanol:

  • Tertiary alkanols react quickly even at room temperature,
  • the reaction of secondary alkanols usually takes a few minutes; sometimes even has to be heated,
  • Primary alkanols react very slowly, with prolonged heating or not at all.

Categories: Fabric Group | alcohol