Examples of Alkenes

We explain the examples of alkenes. In organic chemistry, alkenes are chemical compounds made up of carbon (C) and hydrogen (H), in a chain arrangement of C – C covalent bonds, completed with C – H bonds. Are distinguished because they carry at least one double bond between carbon and carbon, represented as C = C . This double bond can be located at any position in the molecule, this chain being the one that will be taken as the main chain .

The C = C double bond is formed by two types of bonds: the sigma σ bond , made up of the valence electrons of the carbon atoms, and the pi π bond , which arises from the hybridization of the s and p orbitals of the same atoms. carbon. This hybridization occurs when there are no hydrogen atoms close to completing the octet of carbon atoms in the C – H form. The electrons rearrange themselves in a new sp orbital , to bond.

Alkenes are hydrocarbons made up of at least two carbon atoms, since the double bond would occur between them; it is for this that they are also called unsaturated hydrocarbons . They are more reactive than alkanes because it is easier to break the pi π bond. The most important are ethylene CH ₂ = CH ₂ and propylene CH ₂ = CH – CH ₃ , gases that act as fuels and as chemical reagents for the production of polymers: polyethylene and polypropylene .

Ethylene and propylene are in the gaseous state and provide a sufficient amount of heat when burned. After this combustion reaction, they release carbon dioxide (CO ₂ ) and water vapor (H ₂ O). Ethylene, for its part, is used to accelerate the ripening process of fruits in food distributors.

Nomenclature of alkenes

Alkenes are named taking into account the one containing the double bond as the main chain. Starting from the end to which the bond is closest , the positions are counted until the C = C is identified. The position number is written , followed by the name of the hydrocarbon chain , ending with the suffix -eno .

For example:

1-butene: CH ₂ = CH – CH ₂ –CH ₃
2-butene: CH ₃ –CH = CH – CH ₃
1-pentene: CH ₂ = CH – CH ₂ –CH ₂ –CH ₃
2-pentene: CH ₃ –CH = CH – CH ₂ –CH ₃
3-hexene: CH ₃ –CH ₂ –CH = CH – CH ₂ –CH ₃

If the chain has two or more double bonds, the number prefix “di, tri” is added to the name of the hydrocarbon.

For example:

1,3-butadiene CH ₂ = CH-CH = CH ₂
1,4-pentadiene CH ₂ = CH-CH ₂ -CH = CH ₂
1,5-hexadiene CH ₂ = CH-CH ₂ -CH ₂ -CH = CH ₂
2,4-pentadiene CH ₃ -CH = CH-CH = CH ₂
2,4-hexadiene CH ₃ -CH = CH-CH = CH-CH ₃