Homologous series

In chemistry there is a group of organic substances differing similar properties and united by a common formula that describes the pattern of structural differences of each subsequent member of the group from the previous one.For example, a homologous series of alkanes, alkenes, alkynes, or other groups.This nomenclature is of great importance for research, forecasting and practical application.For organic substances combined in a group, there are consistent changes of chemical and physical properties, and they are correlated with the change in molecular weight.

Equally important are rules that describe how the properties of substances in the transition from one group to another.To understand what is a homologous series, should consider concrete examples.For any group of compounds are increasing the characteristic temperature of melting (crystallization), boiling point (condensing) and density with increasing molecular weight and the number of carbon atoms in the molecule.

Saturated hydrocarbons are called saturated or paraffin;they represent acyclic (no cycles) Compounds of normal or branched structure, the atoms in the molecules of which are joined by single bonds.The total formula is CnH2n + 2 and describes a homologous series of alkanes.Molecules of each subsequent member increases as compared with the previous one C atom and two atoms of H. K saturated hydrocarbons include:

  • methane;
  • ethane;
  • propane and so on.

to saturated hydrocarbons also include cycloparaffins.This is a large group of organic compounds whose molecules are closed rings.Homologous series of them has the formula CnH2n, begins with a chemical to three carbon atoms.Examples of cycloparaffins:

  • cyclopropane;
  • cyclobutane;
  • cyclopentane and so on

Unsaturated or unsaturated hydrocarbons are also acyclic.These are the normal and isomeric structure of matter.Homologous series of alkenes having the general formula CnH2n.These compounds are characterized by the presence of one double bond between two carbon atoms.If the previous row starts with a hydrocarbon with a carbon atom (methane), that begins with a substance which contains in the molecule two carbon atoms.Examples of alkenes:

  • ethene;
  • propyl;
  • butene and so on.

hydrocarbon molecule which two carbon atoms connected by triple bond are more unsaturated, otherwise referred to as acetylene.They are united by a homologous series of alkynes.It is described by the formula CnH2n-2 and begins with acetylene, in the formula which has two atoms C. Examples of alkynes:

  • ethyne;
  • propyne;
  • butyn-1 and so on.

unsaturated acyclic hydrocarbons in which the molecule has two double bonds are said diene.They have the general formula CnH2n-2.Their homologous series starts with a hydrocarbon with three carbon atoms in the molecule.The double bonds may be conjugated (separated by one single bond) Cumulated (located on adjacent atoms) or isolated (Separate multiple single bonds).Examples of diene:

  • 1,2-propadiene;
  • 1,3-butadiene;
  • isoprene etc.

particular chemical group to form a cyclic structure in the molecule has a benzene ring.Homologous series of simple aromatic compounds begins with six carbon atoms - benzene.Homologues of this series are formed by substituting one or more hydrogen atoms attached to the benzene ring on radicals.Thus, a number of substances: benzene, toluene, xylene.If the molecule has two or more substituents that indicate the presence of isomers of these substances.Other homologous series of aromatic compounds are derived from naphthalene, anthracene, and other substances.

If the hydrocarbon molecule has a functional group, such chemicals also form a homologous series.

  • number of alcohol characterized by the presence in the molecule of the hydroxyl group (-OH).For monoalcohols one hydrogen atom in an acyclic hydrocarbon substituted by a hydroxyl group;their formula: CnH2n + 1OH.There are rows of polyhydric alcohols.
  • Several phenols characterized by the presence in the molecule and a hydroxyl group (-OH), but it replaces hydrogen on the benzene ring.
  • number of aldehydes per molecule characterized by the presence of the chemical compound of the carbonyl group (& gt; C = O);aldehydes of the general formula: R-CH = O.
  • number ketones also distinguished by the presence of the carbonyl group (& gt; C = O), but if it is connected with aldehydes a radical, then the two ketones hydrocarbon radical.Ketones formula: R1-CO-R2.
  • number of carboxylic acids differ from other chemicals carboxyl group that combines a carbonyl and hydroxyl groups.Formula - RCOOH.

For each series, whether it is a homologous series of aldehydes, carboxylic (organic) acids, alcohols or other substances, their properties will largely depend on the type of functional groups and naturally change along with increasing molecular weight substances.This classification is a broad class of chemical compounds helps to understand nature and to study their properties.