Physical and chemical properties of alicyclic hydrocarbons

Physical and chemical properties of alicyclic hydrocarbons

The alicyclic hydrocarbons are

 

Hydrocarbons having a closed chain of carbon atoms including the carbon atoms in position sp3-, sp2-and sp-hybridisation

 

Physical properties

 

Cyclopropane and cyclobutane are gases remaining alicyclic compound are liquid or solid substance. Cycloalkanes have boiling at 10-20 ° C higher, and a density 20% greater than the corresponding n-alkanes. For strained alicyclic compounds with small and medium cycles characteristic abnormally high heat of combustion.

In general, the physical properties of cycloalkanes largely resemble saturated acyclic hydrocarbons.

 

Chemical properties

 

The most important feature of the molecular structure of alicyclic hydrocarbons is the presence of cyclic moiety of various sizes. Therefore, the complex chemical properties of these compounds will be primarily determined by the stability of cycles. Many reactions  are accompanied by ring-opening reaction . In these reactions, exhibit high activity of the electrophilic reagent as cyclopropane has high HOMO energy value that corresponds to the low ionization potential ( 5.10 eV). Cyclobutane less prone to ring-opening reactions . Cyclopentane and cyclohexane behave similarly to the corresponding alkanes and prone to radical substitution reactions .

Hydrogenation (reduction)

 

This reaction proceeds differently for different alicyclic hydrocarbons. Lower cycloalkanes, and primarily cyclopropane to react the ring opening. Thus cyclopropane exhibits the highest reactivity. For example, reaction over a nickel catalyst molecule at 80C discloses cyclopropane, and cyclobutane - at 200C. When using a platinum catalyst are disclosed cyclopropane at room temperature, cyclobutane - at 50C:

Hydrogenation reaction of cyclopropane and cyclobutane to propane and n-butane.

Five-membered ring is revealed only at high

temperatures.

Compounds with a six-membered cycle heating with hydrogenation dehydrogenation catalysts and are converted into aromatic compounds:

 

 

 

 

reaction of cyclohexane over a platinum catalyst.

 

 

Hydrogalogenation and the action of mineral acids

 

Cyclopropane and its homologues react with a halohydrogens ring with opening in accordance with the Markovnikov rule.

 

 

 

Reaction of ethylcyclohexane with hydrogen bromide.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Cycloparaffins with a large number of carbon atoms, including cyclobutane, do not react with hydrogen halides.

Under the influence of strong mineral acids cyclopropane also bursting with an alcohol:

 

 

 

 

action of a mineral acid to cyclopropane.

 

Halogenation.

 

Reactions of cycloparaffins with halogens are in various directions depending on the cycle. Cyclopropane and its homologues react with the halogen-opening cycle. Cyclopentane and cyclohexane take conventional substitution. Cyclobutane react in both directions.

 

 

 

 

 

 

 

action halogens with cycloalkanes.

Oxidation.

 

All cycles are oxidized with the break cycle and formation of dicarboxylic acids with the same number of carbon atoms as the original cycloalkane. They differ from the isomeric olefins are oxidized to form acids and carbonyl compounds with fewer carbon atoms.

 

 

 

 

 

 

oxidation of cycloalkanes.