Hydrocarbon: In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon .
Aromatic hydrocarbons (arenes), alkanes , cycloalkanes and alkyne -based compounds are different types of hydrocarbons.
Types of hydrocarbons
As defined by IUPAC nomenclature of organic chemistry, the classifications for hydrocarbons are:
1. Saturated hydrocarbon: Saturated hydrocarbons are the simplest of the hydrocarbon species. They are composed entirely of single bonds and are saturated with hydrogen. The formula for acyclic saturated hydrocarbons (i.e., alkanes ) is CnH2n+2
2. Unsaturated hydrocarbon: Unsaturated hydrocarbons have one or more double or triple bonds between carbon atoms. Those with double bond are called alkenes . Those with one double bond have the formula CnH2n
3. Aromatic hydrocarbons: Aromatic hydrocarbons also known as arenes , are hydrocarbons that have at least one aromatic ring .
Hydrocarbons can be gases (e.g. methane and propane ), liquids (e.g. hexane and benzene), waxes or low melting solids (e.g. paraffin wax and naphthalene ) or polymers (e.g. polyethylene , polypropylene and polystyrene ).
Catenation: This inherent ability of hydrocarbons to bond to themselves is known as catenation.
Molecular, condensed and structural formula
A molecular formula tells only the numbers of atoms of each element in a molecule of the compound.
A condensed structure shows all atoms, but it omits the vertical bonds and most or all of the horizontal single bonds.
Structural formula suggests the structure of molecules.
Homologous series
In organic chemistry, a homologous series is a series of compounds with the same functional group and similar chemical properties in which each successive member differs by CH2 . The element of homologous series is called homologue.
Homologous series of alcohol:
CH3OH
CH3CH2OH
CH3CH2CH2OH
CH3CH2CH2CH2OH
CH3CH2CH2CH2CH2OH
CH3CH2CH2CH2CH2CH2OH
CH3CH2CH2CH2CH2CH2CH2OH
CH3CH2CH2CH2CH2CH2CH2CH2OH
CH3CH2CH2CH2CH2CH2CH2CH2CH2OH
CH3CH2CH2CH2CH2CH2CH2CH2CH2CH2OH
Alkyl radical: Alkyl radicals are carbon chains that have lost one hydrogen.
CH3CH2CH2 ⁺ is an propyl radical.
Functional group: In organic chemistry, functional groups are specific substituents or moieties within molecules that are responsible for the characteristic chemical reactions of those molecules. The same functional group will undergo the same or similar chemical reaction(s) regardless of the size of the molecule it is a part of. This allows for systematic prediction of chemical reactions and behavior of chemical compounds and design of chemical syntheses.
other concepts on hydro carbons:
According to IUPAC (International Union of Pure and Applied Chemistry) system of nomenclature, meth- word root is assigned to hydrocarbons having one carbon atom. The suffix -ane is assigned to saturated hydrocarbons (also termed as alkane), which are bonded together by a single covalent bond.
The general formula for nomenclature of saturated hydrocarbon is, CnH2n+2.
Where, n=number of carbon atoms
Number of carbon atom in methane, n=1
Therefore, molecular formula of methane=C1H2˟1+2
=CH4
The term paraffin is coined by Reichenbach. Paraffin is made up of two latin words, parum=little and affinis =affinity or rectivity, so the literal meaning of the word parrafin is little affinity or little reactivity. Alkanes have little affinity for other elements or compounds and they take part in chemical reactiond during certain conditons only.Since carbon and hydrogen atoms have very similar electronegativities all the bonds in alkanes are non-polar. As a result, alkanes are not particularly reactive as functional groups go. In fact, it is often convenient to regard the hydrocarbon framework of a molecule as an unreactive support for the more reactive functional groups. So, alkanes are also called paraffins.
The general formula for nomenclature of saturated hydrocarbon is, CnH2n+2.
Where, n=number of carbon atoms
Number of carbon atom in methane, n=1
Therefore, molecular formula of methane=C1H2˟1+2
=CH4
The term paraffin is coined by Reichenbach. Paraffin is made up of two latin words, parum=little and affinis =affinity or rectivity, so the literal meaning of the word parrafin is little affinity or little reactivity. Alkanes have little affinity for other elements or compounds and they take part in chemical reactiond during certain conditons only.Since carbon and hydrogen atoms have very similar electronegativities all the bonds in alkanes are non-polar. As a result, alkanes are not particularly reactive as functional groups go. In fact, it is often convenient to regard the hydrocarbon framework of a molecule as an unreactive support for the more reactive functional groups. So, alkanes are also called paraffins.
Alkenes are termed as olefins ,because they form oily liquids on reaction with chlorine gas.
Ethene (C2H4) is scientific name for ethylene, while ethylene is common name. Ethene belongs to the alkene group of hydrocarbons. Alkene is unsaturated hydrocarbon in which carbon atoms are bonded together by double covalent bonds. Other members of this group such as propene, butene etc are named as propylene, butylene respectively.
Ethene (C2H4) is scientific name for ethylene, while ethylene is common name. Ethene belongs to the alkene group of hydrocarbons. Alkene is unsaturated hydrocarbon in which carbon atoms are bonded together by double covalent bonds. Other members of this group such as propene, butene etc are named as propylene, butylene respectively.
Ethyne (C2H2) is scientific name for acetylene, while acetylene is common name.Acetylene was discovered in 1836 by Edmund Davy, who identified it as a "new carburet of hydrogen". It was rediscovered in 1860 by French chemist Marcellin Berthelot, who coined the name "acétylène". Ethyne belongs to the alkyne group of hydrocarbons. Alkyne is unsaturated hydrocarbon in which carbon atoms are bonded together by triple covalent bonds.
fig. molecular structure of ethyne/acetylene
fig. molecular structure of ethyne/acetylene
When organic compounds of same group are arranged on the basis of the increasing molecular weight then we get a series which is called homologous series. The members of homologous series have the same funtional group, structural formula and they show similar chemical properties. A homologous series is a series of compounds with the same general formula , usually varying by a single parameter such as the length of a carbon chain.
The homologous series of straight-chained alkanes begins methane (CH4), ethane (C2H6), propane (C3H8), butane (C4H10), and pentane (C5H12). In that series, successive members differ in mass by an extra methylene(-CH2- unit) inserted in the chain.
The homologous series of straight-chained alkanes begins methane (CH4), ethane (C2H6), propane (C3H8), butane (C4H10), and pentane (C5H12). In that series, successive members differ in mass by an extra methylene(-CH2- unit) inserted in the chain.
Carbon is typically tetravalent, i.e. is most stable if it has formed four bonds. In a formal (and paper chemical) exercise, take a random alkane for example ethane. Its structure is given below.
H H
| |
H-C-C-H
| |
H H
Now assume you want to draw a new structure with one more carbon atom. For example, assume this carbon atom to be added at the very right. I’m first going to formally pull apart the C−HC−H bond, then formally put in the carbon, connecting it to the left and right. Notice what will be missing:
H H H H H H H H H
| | | | | | . | | |
H-C-C-H => H-C-C· ·H => H-C-C-C-H => H-C-C-C-H
| | | | | | ˙ | | |
H H H H H H H H H
Note how it requires two hydrogens to satisfy carbon’s valencY. This is why the group formally added is CH2: Assuming a carbon inserted into something it needs two additional hydrogens to keep satisfied.
CH2=CH2
fig.moleculare structure of ethene/ethylene.
Hydrocarbon And Their Derivatives
Methane
Molecular formula: CH4
Condense: CH4
Structural formula:
First member of alkane
Uses
The five uses of Methane are:
1. It is used to manufacture water gas or hydrogen gas.
2. It is used in the form of LPG for domestic use.
3. It is used for making printing ink.
4. It is used for making Carbon Black needed for paints and in rubber industries.
5. It is used as a gaseous fuel in industries and household works.
Ethane
Molecular formula: CH3CH3
Condense formula: C2H6
Structural formula:.......
Second member of alkane family
Uses
1. Used as gases fuel
2. Preparing the organic compounds Alcohol
Alcohol: Organic compounds containing the hydroxyl group attached to saturated carbon atoms or hydrocarbon radicals are known as alcohol.
Ethyl –alcohol (C2H5OH)
Structural formula:
Preparation
By oxidation of glucose in the presence of yeast
C6H12O6 → 2C2H5OH + 2CO2
Physical properties of alcohol:
1. It is colorless liquid but has taste
2. It is soluble in water.
3. Its boiling point is 78 C and freezing point is -114 C.
The uses of alcohol are as follows:
I. It is used for dry cleaning.
II. It is used as alcoholic beverage.
III. It is used in making paint, varnish, medicine, synthetic rubber etc
Glycerol [ C3H3(OH)3 ]
Glycerol is the simplest trihydric alcohol. It occurs in almost all the natural animal fats and vegetable oils. It is proposed by hydrolysis of fat or oil in presence of alkali.
Physical properties
Soluble in water
Colorless viscous liquid
Sweat taste
The uses of glycerol are as follows:
I. It is used to make toilet soaps and cosmetic goods.
II. It is used to make printing inks and stamp pad inks.
III. It is used for the preservation of tobacco, fruits and other edible substances.
Some important questions
1. What is hydrocarbon?
Ans: A compound made up of hydrogen and carbon only is called hydrocarbon.
2. What is an alkane?
Ans: The hydrocarbon in which all the four valencies of a carbon atom are used as a single covalent bonds is called an alkane.
3. What is an alkene?
Ans: An unsaturated hydrocarbon in which the two carbon atoms are connected by a double bond is called an alkene.
4. What is an alkyne?
Ans: An unsaturated hydrocarbon in which the two carbon atoms are connected by a triple bond is called an alkyne.
5. What is structural formula?
Ans: The chemical formula which shows the structure of a molecule is called structural formula.
6. What is condensed formula?
Ans: The shorthand representation of structural formula is called condensed formula.
7. What is glycerol?
Ans: Glycerol is a derivative of propane, obtained by the replacement of three hydrogen atoms from different carbon atoms by three hydroxyl groups.
8. What are saturated hydrocarbons?
Ans: The hydrocarbons in which all the carbon atoms are linked through single bonds are called saturated hydrocarbons.
9. Write any two applications of glucose.
Ans: The two applications of glucose are :
a. Glucose is the most important source of energy for cellular respiration.b. Glucose is stored as starch in plants and glycogen in animals.
10. What is homologous series?
Ans: A series of compounds which have general formula, general methods of preparation and similar chemical properties are called homologous series.
11. What is a functional group?
Ans: A functional group is an atom or group of atoms which defines the structure of a particular family of organic compounds.
12. What are unsaturated hydrocarbons?
Ans: The hydrocarbons in which at least one of the carbon-carbon linkages is with double bond or triple bond are called unsaturated hydrocarbons.
13. What is organic chemistry?
Ans: The branch of chemistry in which we study about organic compounds is called organic chemistry.
14. What is an alcohol?
Ans: Alcohol is an organic compound containing the hydroxyl group attached to a saturated carbon atom or a hydrocarbon radical.
15. What are monohydric alcohols?
Ans: The alcohols which contain one hydroxyl group are called monohydric alcohols.
16. What are dihydric alcohols?
Ans: The compounds containing two hydroxyl groups are known as dihydric alcohols.
17. What are trihydric alcohols?
Ans: The compounds containing three hydroxyl groups are known as trihydric alcohols.
18. How is ethyl alcohol prepared?
Ans: Ethyl alcohol is prepared by the decomposition of glucose in the presence of the enzyme zymase.