Organic compounds are classified according to the type of elements and bonds present in the molecules. Compounds containing only carbon and hydrogen are called hydrocarbons. However organic compounds can also contain elements other than carbon and hydrogen-like oxygen, nitrogen, sulfur, phosphorus, silicon, etc.
Hydrocarbons are further classified as aliphatic and aromatic hydrocarbons based on their structure.
Aliphatic hydrocarbons are either a straight chain, branched or cyclic compounds either containing saturated bonds or unsaturation. While the straight chain and/or branched structure are aliphatic structure, the ring structure is called alicyclic compounds.
These aliphatic hydrocarbons can be further classified as alkanes, alkenes, and alkynes. Alkanes are saturated hydrocarbons. Alkene and alkynes contain unsaturation in the form of double and triple bond respectively. These compounds have a common name, but generally, they are denoted by IUPAC nomenclature. Few examples are as follows:
Alkane: Methane, ethane, etc
Alkene: ethylene, propylene, etc
Alkynes: ethyne, propyne, etc
Aromatic hydrocarbons are compounds, on the other hand, are cyclic ring structure containing 4n+ 2 numbers of delocalized electrons. These compounds often contain benzene rings as a part of the structure. These molecules are planar in nature and have a single bond length which is in between C-C and C=C bond length.
Benzene, toluene, naphthalene, etc.