What is hydrocarbon?
Hydrocarbon like aliphatic, aromatic, or polynuclear aromatic hydrocarbons are types of organic compounds processing hydrogen and carbon in the entire molecular formula. They contain at least one single, double or triple bond in two adjacent carbon atoms.
- When organic compounds formed by two or more carbon atoms by a single chemical bond are called saturated hydrocarbons.
- If the compound containing at least one pair of adjacent carbon atoms liked by multiple chemical bonds are called unsaturated hydrocarbons in organic chemistry.
Structure of hydrocarbons
The valence shell electronic configuration of carbon in hydrocarbons molecule, 2s2 2px1 2py1 2pz. When the electron from 2s-orbital promotes to vacant 2pz-orbital and hybridization to form four equivalent sp3 hybrid orbitals.
These four hybridized orbitals of carbon atoms mix with the hydrogen atom to form saturated organic compounds. But for sp2 and sp-hybridization, the carbon atom is not saturated by valency four.
Chemical properties of hydrocarbon
The solubility of hydrocarbons shows that hydrocarbon molecule is almost insoluble in water but rapidly soluble in alcohol or ether solution. When we are concerned with alkanes, the attractive forces are only weak Van der Waals forces.
The dipole moment of hydrocarbon like all alkanes whether straight or branched-chain will be zero. Zero polarity of these hydrocarbons is associated due to balancing the C-H covalent bond by the remaining alkyl functional group.
The position of the electromagnetic spectrum region of the C-H group depends on the carbon atom. Therefore, the stretching frequency region of hydrocarbons is in the following order, primary carbon > secondary carbon > tertiary carbon.
Classification of hydrocarbons
According to the reactivity, hydrocarbons are classified into two main classes,
- Saturated hydrocarbons: The term saturated means carbon saturated by valency four.
- Unsaturated hydrocarbons: Unsaturated carbon is not saturated by valency four.
According to the structure in chemistry, hydrocarbons are classified into two types, open-chain and cyclic or closed-chain saturated and unsaturated organic compounds present in our environment.
The list of organic compounds that contain two or more carbon atoms linked by only a single chemical bond is named by the term saturated compounds or hydrocarbons.
- Methane, ethane, propane, butane, and pentane are examples of open chain saturated hydrocarbons because these compounds are formed by carbon and hydrogen bonding.
- Cycloalkanes (cyclopropane, cyclobutane, cyclopentane, cyclohexane) are examples of cyclic saturated hydrocarbons.
The compound that contains at least one multiple bond in adjacent carbon atoms is called an unsaturated hydrocarbon.
- If the organic compounds have at least one double bond, they are called alkenes or olefin.
- If organic compounds have at least one triple bond, they are called alkynes (acetylene) respectively.
- In acetaldehyde, the multiple bonds between adjacent carbon and an oxygen atom are not considered for unsaturation.
Alkane, alkene, and alkyne
- Alkanes or paraffin is the saturated type of hydrocarbons that contain single bonds on adjacent carbon atoms obtained from natural sources like crude petroleum oil. The general molecular formula of alkanes is Cn H2n+2.
- Alkene or olefin is the unsaturated hydrocarbon that contains at least one double bond or olefinic chemical bond on two adjacent carbon. The general molecular formula of alkenes is CnH2n.
- Alkyne is an organic hydrocarbon that contains at least one triple bond or acetylenic bond on two adjacent carbon atoms with the general molecular formula CnHn.
When the carbon and hydrogen atoms formed a closed ring structure is called carbocyclic or homocyclic compounds. The cyclic compounds show aliphatic characteristics named alicyclic hydrocarbons. The saturated types of cyclic hydrocarbon take the name of the corresponding open-chain hydrocarbons, proceeds by the suffixes cyclo.
These compounds are collectively called cycloparaffins or cycloalkanes. If the cyclic hydrocarbon is unsaturated, then this hydrocarbon is called cycloalkenes.
Aliphatic and aromatic compounds
With the development of learning chemistry, organic compounds are divided mainly into two types which are pronounced as aliphatic and aromatic hydrocarbons.
The aliphatic naming of hydrocarbon is given from fatty acids but today these compounds are known as open-chain compounds. Therefore, several examples of saturated or unsaturated hydrocarbons come from natural sources named aliphatic hydrocarbon.
The aromatic type name of hydrocarbon is obtained from the Greek prefixes aroma meaning fragrant smell. The detailed characteristics show that the aromatic hydrocarbon compound contains the ring with the aromatic property.
Most of the hydrocarbon molecules are related to the benzene ring or derivative of benzene. The cyclic benzenoid compound has aromatic properties but the properties of these compounds totally different from the alicyclic hydrocarbon molecules.
Natural crude oil or mineral oils are the main sources of aliphatic, aromatic, and cyclic hydrocarbons like methane, ethane, propane, cycloalkene, etc.
When the natural gas does not contain hydrocarbons above ethane is called lean or dry gas. If it contains the higher member of hydrocarbons are called rich or wet gases.
What are the components of crude oil?
Crude petroleum oil of our earth’s environment contains mainly gases with naturally occurring hydrocarbon in the forms of liquified or solid dissolved in liquid solvents.
The density and composition of crude petroleum oil vary with the locality of occurrence but all saturated organic compounds are mainly liquid hydrocarbon. Therefore, crude petroleum oil contains a list of isoparaffinic alkanes, cycloalkenes or naphthenes, and aromatic or polynuclear aromatic hydrocarbons.
Hydrocarbons in petroleum
Naturally, crude oil is classified into two types, paraffinic and asphaltic which contains hydrocarbon compounds like alkane and naphthalene.
- According to this classification crude oil from Pennsylvania, Iran and Rumania contain paraffinic type.
- From Baku, Venezuela is an asphaltic type of hydrocarbon.
- From Texas, Mexico, Oklahoma is an intermediate type of hydrocarbon.
Natural gas composition
The term natural gas means the total quantity of gaseous hydrocarbon present in used liquid gases. Therefore, the main component of natural gas varies according to the source.
Natural gas consists chiefly of the first six alkanes or hydrocarbons and the percentage of occurrence decreases with increasing molecular weight.
Fractional distillation of natural gas
The hydrocarbon separated from natural gas by fractional distillation under pressure uses for different energy generation purposes in our daily life.
Oxidation of natural gas under controlled conditions produces a mixture of organic aldehyde, acid, acetone, and alcohol which we use in the different chemical industries.
Hydrocarbons like methane, ethane, propane, butane, pentane, and hexane are obtained when natural gas combustion at about the temperature of 200 to 300°C with 1-200 atm pressure in presence of a chemical catalyst.
Cracking of hydrocarbon
The thermal bond dissociation of organic molecules like hydrocarbon is known as pyrolysis. Thermal creaking produces a list of hydrocarbons or classes of alkanes from the higher member of the alkane family.
Alkane decomposed to lower alkanes by specific heat like 500°C to 600°C. The product obtained from a given alkane depends on, structure, applied pressure, and used catalyst.
- The thermal decomposition of a list of hydrocarbons like decane given lower alkane octane and ethylene.
- If we use suitable catalysts, alkanes containing six or more carbon atoms are cyclized. Therefore, in the presence of the chemical element platinum as a catalyst, hydrocarbon decane is cyclized to form benzene.
Cracking of petroleum
Organic fuels like petroleum oil creaking are used for the extraction of the most common list of liquid hydrocarbons like aliphatic, aromatic, and polyaromatic hydrocarbons.
For example, the most important list of hydrocarbons like methane, ethane, ethane, propane, butane, and isobutene obtains from organic fuels that contain up to four carbon atoms in their molecular formula.