Definition of Hydrocarbons
The organic compounds belonging to organic chemistry which deals with the study of carbon and hydrogen atoms and their derivatives are called hydrocarbons. For example; coal, petroleum, natural gas, and tar. The number of these compounds is very large because it shows the property of catenation.
Division of Hydrocarbons
They are divided into two categories. 1st one is called saturated and the 2nd one is called unsaturated Hydrocarbons.
Saturated Hydrocarbons
The organic compounds which contain only a single bond between the atoms of carbon to form a linear or a branch chain structure are called saturated hydrocarbon. For example; Methane, Ethane, Propane, etc.
Properties of Saturated Hydrocarbons
- They have lower densities than water and are not soluble in water.
- With increased carbon chain length or ring size, melting and boiling points rise.
- They undergo two essential reactions: combustion and halogenation.
Unsaturated Hydrocarbons
The organic compounds which contain double or triple bond between the atoms of carbon to form along the chain or a cyclic structure is called unsaturated hydrocarbons. For example; Cyclopentane, Cyclohexane, Benzene, etc.
Properties of Unsaturated Hydrocarbons
- They have a weaker intermolecular force because they are nonpolar.
- As a result, they are poorly soluble in water but totally soluble in nonpolar organic solvents such as Benzene.
- They are distinguished by the existence of double or triple-covalent connections between carbon atoms.
Classification of Hydrocarbons
There are several organic compounds found in nature. In addition to being present in fossil fuels, they are also found in trees and plants, such as carotenes, which are found in carrots and green leaves. More than 98 percent of natural crude rubber is a hydrocarbon polymer, which is a chainlike molecule made up of several connected units. Individual organic compound structures and chemistry are heavily influenced by the sorts of chemical bonds that connect the atoms of their constituent molecules.
They were classed as aliphatic or aromatic by nineteenth-century chemists based on their origins and features. Aliphatic organic compounds (from Greek aleiphar, “fat”) were produced from the chemical breakdown of fats or oils. Aromatic organic compounds were a class of related compounds derived from the chemical breakdown of some pleasant-smelling plant extracts. Modern nomenclature retains the labels aliphatic and aromatic, but the chemicals they describe are differentiated by structure rather than origin.
There exist 2 main groups of Hydrocarbons. 1st one is Aliphatic and the 2nd one is Aromatic Hydrocarbons.
Aliphatic organic compounds are classified into three classes based on the sorts of bonds they contain: alkanes, alkenes, and alkynes. Alkanes have just single bonds, alkenes have a double carbon-carbon link, and alkynes have a triple carbon-carbon bond. Aromatic organic compounds are ones that are much more stable than their Lewis structures would imply; in other words, they have “special stability.” They are divided into two types: arenes, which have a benzene ring as a structural unit, and non-benzenoid aromatic organic compounds, which have remarkable stability but do not have a benzene ring as a structural unit.
Aliphatic Hydrocarbons
The organic compounds in which there exist only a chain of carbon atoms that are connected with each other through single, double, or triple bond is called Aliphatic Hydrocarbons. These compounds are further divided into three types which are Alkanes, Alkenes, and Alkynes. Its structure will be like an open chain linear or branched and closed chain or cyclic. The Benzene ring is not present in these compounds. For example; Butane, Butene, Butyne, and cyclo-butane.
Properties of Aliphatic hydrocarbons
- When the molecular masses of two alkanes are equivalent, the more heavily branched alkane has a lower boiling point.
- Aliphatic compounds’ melting points rise with size but in an unusual way.
- These molecules can contain compact chains or rings of carbon atoms.
Aromatic Hydrocarbons
Aromatic originated from the word Aroma which means pleasant smell. The compounds in which the Benzene ring (the Carbon atom is attached to the Hydrogen atom with the help of alternative single and double bonds) is present are called Aromatic Hydrocarbons. These compounds are also called Arenes. The simplest Aromatic Hydrocarbon is Benzene C6H6. The group of Aromatic compounds is named a phenyl group.
Properties of Aromatic hydrocarbons
Benzene was the first chemical to be classified as an aromatic organic compound. It is also the most sophisticated aryl hydrocarbon. Each carbon atom in the benzene ring possesses two carbon-carbon sigma bonds, one carbon-hydrogen sigma bond, and one delocalized double bond with a neighboring carbon.
A circle inside the hexagon represents the delocalization of pi electrons in the benzene molecule. The bond order of all carbon-carbon bonds in this molecule is 1.5, and this equivalence may be explained using benzene resonance structures.
The following are some general characteristics of aromatic organic compounds.
- These chemicals are aromatic (additional stability granted by resonance).
- In these compounds, the carbon-to-hydrogen atom ratio is relatively high.
- When aromatic organic compounds are burned, they produce a yellow, sooty blaze.
- Electrophilic substitutions and nucleophilic aromatic substitution processes are common in these molecules.
- It is worth noting that these compounds might be monocyclic or polycyclic.
Types of Aliphatic hydrocarbons
There are 3 main types of Aliphatic hydrocarbons which are Alkanes, Alkenes, and Alkynes.
Alkanes
The organic compounds in which carbon atoms are attached to other carbon atoms through single covalent bonds are called Alkanes. If the molecule doesn’t have a ring structure, its formula is CnH2n+2.
These are the simplest class of hydrocarbons, alkanes are also the most common. Just carbon and hydrogen may be found in them. There are four bonds between carbon atoms and one between hydrogen atoms. Line-angle formulae are preferred by chemists because they are less time-consuming to draw than more compact structural formulas. Alkane structural formulae can be expressed in still another compact form.
Examples
Methane CH4, Ethane C2H6, Propane C3H8, etc are examples of Alkanes. Methane, the simplest alkane, has a chemical formula of CH4 and consists of a single carbon atom. Due to the presence of just single covalent bonds, the structural formula of this molecule is
Physical properties of Alkanes
The physical properties of Alkanes are as follows:
- First, four members of the alkane series are gases, the next thirteen members are liquids and all the next are solids.
- All the alkanes are water-insoluble and dissolve in organic solvents like ether, acetone, benzene, hexane, and carbon tetrachloride.
- Melting points, boiling points, and specific gravities increase with the rise in molar masses. For an increase in every -CH₂-group, there happens an increase of B.P. by 20°C.
- The boiling points of branched-chain alkanes are lower than isomeric normal alkanes. Alkanes with an even number of carbon atoms have higher melting points than the neighboring compounds.
- CH4 is perfectly tetrahedral and all the bond angles are exactly 109.50 C, but higher alkanes like propane, butane, pentane, etc. have zig-zag structures and their bond angles deviate from 109.50 C.
Chemical properties of Alkanes
The chemical properties of Alkanes are as follows:
- Alkanes are relatively stable to common reagents. Acids, bases, and oxidizing agents don’t react with alkanes at room temperature.
- Alkanes burn in O₂ to give CO₂ and H₂O and evolve a large amount of heat. So, they are used as fuels. The amount of heat evolved per mole of an alkane is called the heat of combustion.
- When CH4 is oxidized in the presence of Cu as a catalyst at high temperature and pressure, CH, OH, HCHO, and HCOOH are obtained.
- Nitration of alkanes is a substitution reaction and happens in the presence of conc. HNO3 at high temperature. The higher alkanes break their C – C bonds to give their nitro derivatives.
- Halogenation of alkanes gives alkyl halides. The order of reactivity of halogens is F₂ > Cl₂ > Br2 > I2. Cl₂ reacts with alkanes in the presence of ultraviolet light or diffused sunlight or at high temperatures with the free radical mechanism.
Alkenes
The Acyclic compounds (branch or unbranched in nature) in which carbon atoms are attached to the other carbon atoms of the chain through a double bond are called alkenes. These hydrocarbons are unsaturated in nature because of the presence of a double bond in them. Their general molecular formula is CnH2n .
Examples
Ethene (C2H4) is the most common example of Alkenes. The double bond in alkenes is traditionally thought to consist of a sigma (σ ) component and a pi (π ) component of the bond.
Properties of Alkenes
- The reactivity of alkenes is due to the presence of л-bond. л-bond is weaker as compared to σ. The reactions of different types which are given by alkenes are addition reactions, oxidation reactions, and polymerization reactions.
- In addition reactions, we can add hydrogen, halogens, halogen acids and HOX. Every reaction has its own conditions. If alkene is unsymmetrical, then Markownikoff’s rule is obeyed.
- In oxidation reactions, oxygen can be added at the double bond in the presence of Ag at 300°C to form epoxide.
- Alkenes undergo ozonalysis to give aldehydes and ketones through a five membered molecule called ozonide.
- The polymerization of ethene gives polythene when it is subjected to 400°C temperature, 100 atm. pressure and traces of oxygen.
- Ethene is used for artificial ripening of fruit, as a general anesthetic, for the preparation of many chemicals and for preparation of mustard gas which is used in war-fare.
Alkynes
The organic compounds in which carbon atoms are attached to other carbon atoms through triple covalent bonds are called Alkynes. To simplify things, molecules with one triple bond have the formula CnH2n-2 (and no rings). Due to the existence of two p-bonds in the triple bond, alkynes are able to conduct many of the same reactions as alkenes, but at twice the rate. The triple bond which is present in Alkynes is also known as the Acetylenic bond.
Examples
There are several alkynes in nature. The first of the alkynes, ethyne (C2H2) has a triple bond between its two carbon atoms.
Physical properties of Alkynes
- Alkynes are colourless and odourless substances except acetylene which has a garlic-like odour.
- The first three members of alkynes up to C4H, are gases, the next eight members up to C12H22 are liquids and the higher members are solids.
- The melting and boiling points of alkynes increase gradually with the increasing molar masses along with an increase in densities.
- Alkynes are non-polar substances and are dissolved readily is non-polar solvents like ether, benzene and carbon tetrachloride.
Chemical properties of Alkynes
- Alkynes undergo addition reactions with hydrogen to give alkanes Halogens are added to give tetrahalides. Halogen acids add to give germinal dihalides.
- Water adds on alkynes in the presence of HgSO4 and H₂SO4 to give aldehydes and ketones.
- Addition of NH3 on acetylene at 300°C in the presence of Al2O3 gives methyl nitrile, while addition of HCN in the presence of Cu₂Cl₂ and NH₂Cl gives us acrylonitrile.
- Ethyne reacts with oxygen to give CO₂ and H₂O and reaction is highly exothermic. Oxy-acetylene flame is produced which creates a temperature of 3500°C.
- When alkynes are treated with alkaline KMnO4 tetrahydroxy alkanes are produced which are further oxidized to suitable carboxylic acids.
FAQ’s
What are 3 unsaturated Hydrocarbons?
In terms of their bond structures, unsaturated hydrocarbons may be broken down into three categories: alkanes, alkenes, alkynes, and aromatic hydrocarbons.
Is fire a hydrocarbon?
Hydrocarbons – referring to the molecular structure of anything – consisting of hydrogen and carbon typically generate considerable vapour emissions, enough to create a flammable concentration which when coupled with oxygen form a volatile molecule. Pool fire and jet fire are both examples of hydrocarbon fires.
Is hydrocarbon a diesel?
Diesel fuel is a combination of hydrocarbons extracted from crude oil, with boiling temperatures ranging from 150 to 380 degrees Celsius. Paraffinic hydrocarbons, naphthenic hydrocarbons (or cycloparaffinic hydrocarbons), and aromatic hydrocarbons are the three main types of hydrocarbons found in petroleum crude oils.
What is the largest hydrocarbon?
Coal, lastly, has the biggest and most complicated hydrocarbon molecules. Hydrocarbons with varying amounts of hydrogen to carbon have varying effects on the environment, including the release of water and carbon dioxide. For the most part, the carbon-to-hydrogen ratio increases with molecule length and complexity.
What is the most powerful hydrocarbon?
The most common hydrocarbon in this context, methane, is a potent heat-trapping greenhouse gas that contributes more to climate change when released into the atmosphere unburned than carbon dioxide does when it is burnt.
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