Carbon Compounds

 

Carbon

Atomic Number: 6 

Electronic configurations: 2, 4 

Valence electrons: 4

Property: Non-metal

Abundance: Carbon is the 4th most abundant substance in universe and 15th most abundant substance in the earth’s crust.

Compounds having carbon atoms among the components are known as carbon compounds. Previously, carbon compounds could only be obtained from a living source; hence they are also known as organic compounds.

Bonding In Carbon: Covalent Bond

The bond formed by sharing of electrons is called covalent bond. Two or more atoms share electrons to make their configuration stable. In this type of bond, all the atoms have similar rights over shared electrons. Compounds which are formed because of covalent bond are called COVALENT COMPOUNDS.

Covalent bonds are of three types: Single, double and triple covalent bond.

Single Covalent Bond:

Single covalent bond is formed because of sharing of two electrons, one from each of the two atoms.

Formation of the hydrogen molecule (H2)

Atomic Number of H = 1
Electronic configuration of H = 1
Valence electron of H = 1

Hydrogen forms a duet, to obtain stable configuration. This configuration is similar to helium (a noble gas).

Since hydrogen has one electron in its valence shell, so it requires one more electron to form a duet. So, in the formation of hydrogen molecule; one electron from each of the hydrogen atoms is shared.

Formation of hydrogen chloride (HCl):

Valence electron of hydrogen = 1
Atomic number of chlorine = 17
Electronic configuration of chlorine: 2, 8, 7
Electrons in outermost orbit = 7
Valence electron = 7

Double covalent bond:

Double bond is formed by sharing of four electrons, two from each of the two atoms.

Formation of oxygen molecule (O2):

Valence electron of oxygen = 2

In the formation of oxygen molecule, two electrons are shared by each of the two oxygen atoms to complete their stable configuration.

In oxygen, the total number of shared electrons is four, two from each of the oxygen atoms. So a double covalent bond is formed.

Formation of Carbon dioxide (CO2):

Valence electron of carbon = 4
Valence electron of oxygen = 6

In carbon dioxide, two double covalent bonds are formed.

Triple Covalent Bond:

Triple covalent bond is formed because of the sharing of six electrons, three from each of the two atoms.

Formation of Nitrogen (N2):

Atomic number of nitrogen = 7
Electronic configuration of nitrogen = 2, 5
Valence electron = 5

In the formation of nitrogen, three electrons are shared by each of the nitrogen atoms. Thus one triple bond is formed because of the sharing of total six electrons.

Properties of Covalent Bond:

  • Intermolecular force is smaller.
  • Covalent bonds are weaker than ionic bond. As a result, covalent compounds have low melting and boiling points.
  • Covalent compounds are the poor conductor of electricity as no charged particles are formed in covalent bond.
  • Since, carbon compounds are formed by the formation of covalent bond, so carbon compounds generally have low melting and boiling points and are the poor conductor of electricity.

Organic Compounds

Initially, compounds of carbon could only be obtained from living sources and there was no way of synthesizing them. Hence, carbon compounds are also known as organic compounds. Carbon forms a large number of compounds. So far, formulae of about 3 million carbon compounds are known.

Cause of formation of such a large number of compounds by carbon:

  1. Carbon can form bonds with other carbon atoms. This property of carbon is known as CATENATION. Because of catenation, carbon can form a long chain; while making bond with other carbon atoms. Carbon can make single, double and triple bonds by catenation.
  2. Carbon can form bonds with other carbon atoms. This property of carbon is known as CATENATION. Because of catenation, carbon can form a long chain; while making bond with other carbon atoms. Carbon can make single, double and triple bonds by catenation.
  3. Carbon can form branched chain; along with straight chain; while combining with carbon atoms, i.e. because of the property of catenation.

Example:

Carbon can also form bonds with other types of monovalent atoms; apart from carbon. Carbon can make long chain combining with other atoms also. For example, carbon can form bonds with oxygen, hydrogen, nitrogen, etc.

Carbon-carbon bonds are very stable, which makes the compounds of carbon stable.

Hydrocarbon

(Hydrogen + Carbon = Hydrocarbon) Compounds formed because of the combination of hydrogen and carbon are known as hydrocarbons. There are two types of hydrocarbon, viz. saturated hydrocarbon and unsaturated hydrocarbon.

Saturated hydrocarbons: Hydrocarbons having single bonds are known as SATURATED HYDROCARBONS. Saturated hydrocarbons are known as ALKANE. These are also known as paraffin. Example: Methane, Ethane, Propane, etc.

Unsaturated hydrocarbon: Unsaturated hydrocarbons are of two types of Hydrocarbon with double bond and hydrocarbon with triple bond.

Hydrocarbon with double bond: Hydrocarbons having at least one double bond are known as ALKENE. Example: Ethylene, Propylene, Butylene, etc.

Hydrocarbon with triple bond: Hydrocarbons having at least one triple bond are known as ALKYNE. Example: Ethyne, Propyne, Butyne, etc.

Alkane

Hydrocarbons having only single bonds are known as alkane. These are saturated hydrocarbons. Alkane are also known as paraffin. The general formula of alkane is CnH2n+2

If C = 1, then; CnH2n+2 = C1H2x1+2 = CH4

Name of this compound is methane. It can be shown by following structural formula:

If C = 2, then; CnH2n+2 = C2H2x2+2 = C2H6

Name of this compound is ethane. It can be shown by following structural formula:

Structural formula of ethane can also be written as CH3CH3 or CH3 − CH3

If C = 3, then; CnH2n+2 = C3H2x3+2 = C3H8

Name of this compound is propane. It can be shown by following structural formula:

Structural formula of propane can also be written as CH3CH2CH3 or CH3 − CH2 − CH3

If C = 4, then; CnH2n+2 = C4H2x4+2 = C4H10

Name of this compound is butane. It can be shown by following structural formula:

Structural formula of propane can also be written as CH3CH2CH2CH3 or CH3 − CH2 − CH2 − CH3

If C = 5, then; CnH2n+2 = C5H2x5+2 = C5H12

Name of this compound is pentane. It can be shown by following structural formula:

Structural formula of pentane can also be written as CH3CH2CH2CH2CH3 or CH3 − CH2 − CH2 − CH2 − CH3

If C = 6, then; CnH2n+2 = C6H2x6+2 = C6H14

Name of this compound is hexane. It can be shown by following structural formula:

Structural formula of hexane can also be written as CH3CH2CH2CH2CH2CH3 or CH3 − CH2 − CH2 − CH2 − CH2 − CH3

If C = 7, then; CnH2n+2 = C7H2x7+2 = C7H16

Name of this compound is heptane. It can be shown by following structural formula:

Structural formula of heptane can also be written as CH3CH2CH2CH2CH2CH2CH3 or CH3 − CH2 − CH2 − CH2 − CH2 − CH2 − CH3

If C = 8, then; CnH2n+2 = C8H2x8+2 = C8H18

Name of this compound is octane. It can be shown by following structural formula:

Structural formula of octane can also be written as CH3CH2CH2CH2CH2CH2CH2CH3 or CH3 − CH2 − CH2 − CH2 − CH2 − CH2 − CH2 − CH3

If C = 9, then; CnH2n+2 = C9H2x9+2 = C9H20

Name of this compound is nonane. It can be shown by following structural formula:

Structural formula of nonane can also be written as CH3CH2CH2CH2CH2CH2CH2CH2CH3 or CH3 − CH2 − CH2 − CH2 − CH2 − CH2 − CH2 − CH2 − CH3

If C = 10, then; CnH2n+2 = C10H2x10+2 = C10H22

Name of this compound is decane. It can be shown by following structural formula:

Structural formula of decane can also be written as CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3 or CH3 − CH2 − CH2 − CH2 − CH2 − CH2 − CH2 − CH2 − CH2 − CH3

Unsaturated Hydrocarbons

Alkene: Hydrocarbons having at least one double bond between two carbon atoms are known as ALKENE. General formula of alkene is CnH2n; where n is number of carbon atoms.

If C = 1 then CnH2n = C1H2x1 = CH2

Name of this compound: Since hydrocarbon having one carbon atom is known as Methane. Thus, Methane – ane + ene = Methene. But, alkene does not exist with one carbon atom, thus, methene does not exist.

If C = 2 then CnH2n = C2H2x2 = C2H4

Name of this compound is: ethane − ane + ene = ethene. This molecule can be shown by following structural formula.

If C = 3 then CnH2n = C3H2x3 = C3H6

Name of this compound is: butane − ane + ene = butene. This molecule can be shown by following structural formula.

Other alkenes are formed in similar way.

Alkyne

Hydrocarbons having at least one triple bond between two carbon atoms are known as alkyne. (Alkane – ane + yne = Alkyne). Similarly;

Ethane – ane + yne = Ethyne
Propane – ane + yne = Propyne
Butane – ane + yne = Butyne
Pentane – ane + yne = Pentyne

General formula of alkyne is CnH2n − 2. As in case of alkene, minimum two carbon atoms are required to form alkyne.

If C = 2, then; CnH2n − 2 = C2H2x2 − 2 = C2H2

The name of this compound is ethyne. This can be shown by following structural formula.

If C = 3, then; CnH2n − 2 = C3H2x3 − 2 = C3H4

The name of this compound is propyne. This can be shown by following structural formula.

If C = 4, then; CnH2n − 2 = C4H2x4 − 2 = C4H6

The name of this compound is butyne. This can be shown by following structural formula.

Other alkynes are formed in similar way.

Cyclic Hydrocarbon

Carbon can form cyclic structure combining with carbon atoms. Such hydrocarbons are known as cyclic hydrocarbon. Structural formulae of some of the cyclic hydrocarbons are as follows:

Hydrocarbons: Nomenclature

Functional Group: Single atom or group of atoms, that have similar chemical properties are called functional group. For example: Halogen group, Carboxyl group, Aldehyde group, etc.

Alkyl group: −R is known as alkyl group.

Examples: −CH3 (Methyl) −C2H5 (Ethyl), −C3H7 (Propyl)

Halogen group: Halogen group is also known as halo group. −Cl (Chloro),−Br(Bromo),−I(Iodo) are halogen or halo group.

Alcohol: −OH is known as alcohol group.

Aldehyde: −CHO is known as aldehyde group. Its structural formula is as follows:

Ketone Group: −CO− is known as ketone group. This is also known as carbonic group. Its structural formula is as follows:

Carboxylic Acid Group: −COOH is known as carboxylic acid group; or simply as acid group. Its structural formula is as follows:

Nomenclature of Carbon Compounds

International Union of Pure and Applied Chemistry (IUPAC) decided some rules to name the carbon compounds. This was done to maintain the uniformity throughout the world. Names which are given on this basis are popularly known as IUPAC name. The rules for nomenclature are as follows:

Identify the number of carbon atoms in carbon compound. Name the carbon compounds according to the number of carbon atoms.

Example: Saturated hydrocarbon having one carbon atom is named as Methane. Saturated hydrocarbon having two carbon atoms is named as Ethane.

Unsaturated hydrocarbon with double bond having two carbon atoms is named as Ethene.

Unsaturated hydrocarbon with triple bond between carbon atoms is named as Ethyne.

If the structure has branched chain, identify the longest chain and then identify the number of carbon atoms. To understand this, let us observe following examples:

In figure (a) the longest chain has eight carbon atoms, and thus the name of parent compound would be octane. In figure (b) longest chain has nine carbon atoms, and thus the name of parent compound would be nonane.

Identify the longest chain. Then number the carbon atoms in such a fashion that the functional group; if any; would come at the lowest number.

In the given figure (c), while counting from right to left (in red color), branched chain which is functional group falls at the fourth position. On the other hand, while counting from left to right, the branched chain falls at the fifth position. In this case, the numbering from right to left is taken because then only the functional would be at the lowest position.

In case of a functional group present, write the prefix or suffix of the functional group according to the table given here. Then write the name of the parent compound.

Functional group

Prefix

Suffix

Alkyl

Alkyl

n/a

Halogen

Chloro− for chlorine,
Bromo− for bromine 
Iodo− for iodine

n/a

Alcohol

n/a

ol

Aldehyde

n/a

al

Ketone

n/a

one

Carboxylic acid

n/a

oic acid

Double bond

n/a

ene

Triple bond

n/a

yne

Nomenclature of Alkane

Example: In this structure, there are four carbon atoms but no functional group is attached. Hence, its name is butane

Common name: Iso-butane.

IUPAC Name:

Number of carbon atoms in the longest chain = 3.
A methyl group is present at carbon number 2.
So, IUPAC Name is 2-methyl propane.

Example: Since there are five carbon atoms, hence its IUPAC name is pentane. Its common name is n-pentane.

IUPAC Name:

Numbering of carbon atoms is done in two ways, i.e. from left to right and from right to left.

The number of carbon atoms in the longest chain = 4.
A methyl group (functional group) is attached with this chain.
Thus, name of parent compound is Butane.


In the numbering from left to right functional group falls at second number while in the numbering from right to left; the functional group falls at 3rd position.

Therefore, IUPAC name of this compound is 2-methyl butane.

Example: The common name of this compound is neopentane.

IUPAC Name:

There are three carbon atoms in longest chain.
Two methyl groups are present at second (2) carbon atom. (Di is used as prefix for two). 
Therefore, IUPAC Name: Di-methyl propane.

Hydrocarbons: Nomenclature Part 2

Naming of hydrocarbon with Halo group:

Example: (CH3Cl) The common name of this molecule is methyl chloride. There is one carbon atom in this compound. So its parent name is Methane. Since one chloro group is present in this compound, hence its IUPAC name is chloro-methane. Following is the structural formula of chloro-methane.

Naming of alcohol group

Example: CH3OH

The common name of this compound is methyl alcohol.

IUPAC Name:

Number of carbon atom: 1
Functional group: Alcohol (suffix : ol)
IUPAC Name: Methane – e Methane – e + ol = Methanol. 
Following is the structural formula of methanol.

Example: CH3CH2OH

The common name of this compound is ethyl alcohol.

IUPAC Name:

Number of carbon atoms: 2
Functional group: Alcohol
Hence, IUPAC name is ethanol.
Following is the structural formula of ethanol.

Example: C6H13OH

The common name of this compound is hexyl alcohol.

IUPAC Name:

Number of carbon atoms: 6 
Functional group: Alcohol
Hence, its IUPAC name is hexanol
Following is the structural formula of hexanol.

Naming of Aldehyde group (−CHO):

IUPAC name of alkane having aldehyde group is written as follows:

The suffix of aldehyde group is “al”. 
Alkane – e + al = Alkanal
Methane – e + al = Methanal
Ethane – e + al = Ethanal, and so on.

Example: HCHO

Common name of this compound is formaldehyde.

IUPAC Name:

Number of carbon atom: 1 
Hence, IUPAC name is methanal.
Following is the structural formula of methanal.

Naming of Carboxylic Acid (−COOH)

Suffix for carboxylic acid is ‘oic acid”.
Thus an alkane having carboxylic acid is named as:
Methane – e + oic acid = Methanoic acid
Ethane – e + oic acid = Ethanoic acid.

Answer: HCOOH

Common name of this compound is formic acid. It has one carbon atom, hence its IUPAC name is methanoic acid. Following is the structural formula of methanoic acid.

Example: CH3COOH

Common name of this compound is acetic acid. It has two carbon atoms, hence its IUPAC name is ethanoic acid. Structural formula of ethanoic acid is as follows:

Example: C4H9COOH

It has five carbon atoms, hence its IUPAC name is pentanoic acid. Structural formula of pentanoic acid is as follows:

Naming of Ketone (−CO−):

Example: CH3−CO−CH3

Common name of this compound is dimethyl ketone. It has three carbon atoms and functional group is ketone, hence its IUPAC name is propanone. Structural formula of propanone is as follows:

Example: C2H5−CO−C2H5

Common name of this compound is dethyl ketone. It has five carbon atoms and functional group is ketone, hence its IUPAC name is pentnone. Following is the structural formula of pentanone:

Homologous Series

Series of compounds with same general formula and functional group is known as homologous series. Compounds belonging to the same homologous series show similar properties. Compounds of homologous series differ by CH2from their consecutive members. Each subsequent compound in a homologous series differs by 14 au. Example: Alkanes; such as, Methane, Ethane, Propane, Butane, etc. belong to same homologous series.

Properties of Compounds of Same Homologous Series

  1. Compounds of same homologous series have same general formula.
  2. Compounds of same homologous series differ from their consecutive members by one carbon atom and two hydrogen atoms, homologous series differ from their consecutive members by one carbon atom and two hydrogen atoms, i.e. by CH2
  3. Compounds of same homologous series have same chemical properties.
  4. Compounds of same homologous series differ by physical properties with increase or decrease in molecular mass.

Chemical Properties of Carbon Compounds

Combustion Reaction:

Carbon and carbon compounds gives carbon dioxide, vapor, heat and light on burning in air. Following are some of the examples of combustion reaction of organic compounds:

C + O2 ⇨ CO2 + Heat + Light

CH4 + 2O2 ⇨ CO2 + 2H2O + Heat + Light

CH3C2OH + O2 ⇨ CO2 + H2O + Heat + Light

Oxidation:

In combustion reaction, carbon compounds are oxidized in the presence of oxygen. The following example is different because alkaline KMnO4 is the oxidizing agent in this reaction.

CH3CH2OH + (Alkaline KMnO4/Acidified K2Cr2O7) ⇨ CH3COOH

Addition Reaction:

Formation of larger molecules by addition of more radicals is known as addition reaction. For example; ethene is converted into ethane when heated with the catalyst nickel.

CH2=CH2 + H2 + (Nickel catalyst) ⇨ CH3−CH3

When ethene undergoes addition reaction with chlorine, it gives dichloroethane.

Substitution Reaction:

Replacement of a functional group or any atom by another atom or functional group is known as substitution reaction. Substitution reactions are single displacement reactions.

When methane reacts with chlorine gas in the presence of sunlight, it gives chloromethane and hydrogen chloride.

CH4 + Cl2 + Sunlight ⇨ CH3Cl + HCl

Similarly, ethane gives chloroethane when it reacts with chlorine in the presence of sunlight.

C2H6 + Cl2 + Sunlight ⇨ C2H5Cl + HCl

Some Important Organic Compounds

Ethanol (C2H5OH)

  • Ethanol is commonly known as alcohol and spirit.
  • General name of ethanol is ethyl alcohol.
  • Ethanol is the main constituent of all alcoholic drinks
  • Ethanol is soluble in water
  • Ethanol is a very good solvent
  • Ethanol is used in manufacturing of medicines, such as tincture iodine, cough syrup, etc.
  • Taking even small quantity of pure ethanol may prove lethal
  • Taking dilute ethyl alcohol can cause drunkenness

Reaction of ethanol with sodium metal:

When ethanol reacts with sodium, it gives sodium ethoxide and hydrogen gas.

2CH3CH2OH + 2Na ⇨ 2CH3CH2ONa + H2

Oxidation of ethanol: Ethanol gives ethanoic acid on oxidation.

CH3CH2OH + (Alkaline KMnO4/Acidified K2Cr2O7) ⇨ CH3COOH

Dehydration of ethanol: Ethanol gives ethene and water when it is heated with concentrated sulphuric acid.

CH3CH2OH + Conc. H2SO4 ⇨ CH2=CH2 + H2O

Ethanoic Acid (CH3COOH)

Structural formula of ethanoic acid is as follows:

  • General name of ethanoic acid is acetic acid.
  • Melting point of ethanoic acid is 290K.
  • Ethanoic acid freezes in winter and hence it is also known as glacial acetic acid.
  • Ethanoic acid is a colorless liquid.
  • 5% to 8% solution of acetic acid in water is known as vinegar.
  • Vinegar is used as preservative in pickles.
  • Carboxylic acids are weak acid compared to mineral acids.
  • Reaction of ethanoic acid with base: Ethanoic acid gives sodium acetate when it reacts with sodium hydroxide.
  • CH3COOH + NaOH ⇨ CH3COONa + H2O
  • Esterificaiton of ethanoic acid: Ethanoic acid gives ethyl acetate when it reacts with ethanol in presence of conc. sulphuric acid. This reaction is called esterification reaction.
  • CH3COOH + C2H5OH ⇨ CH3COOC2H5+ H2O
  • CH3COOC2H5+ NaOH ⇨ CH3COONa + C2H5OH
  • Saponification:Ester of higher fatty acids gives sodium salt of higher fatty acid; when heated with glycerol and sodium hydroxide. Sodium salts of higher fatty acid are known as soaps. This reaction is called saponification (soap making).
  • Reaction of ethanoic acid with sodium carbonate and sodium bicarbonate:
  • Ethanoic acid gives sodium acetate, water and carbon dioxide when reacts with sodium carbonate or sodium bicarbonate (sodium hydrogen carbonate).
  • 2CH3COOH + Na2CO3⇨ 2CH3COONa + CO2 + H2O
  • CH3COOH + NaHCO3⇨ CH3COONa + CO2 + H2O

Soaps and Detergents

Soap: 

Ester of higher fatty acids is called soap. It is manufactured by the reaction of ester of higher fatty acid with sodium hydroxide. The sodium salt so formed has cleansing property.

Detergent: 

Soap cannot form lather in hard water. To overcome this problem, detergents were introduced. Detergent is also known as soapless soap. Detergent is sodium salt of benzene sulphonic acid or sodium salt of long chain alkyl hydrogen sulphate.

Cleansing action of soap:

Soap molecule has two ends. One end is hydrophilic and another end is hydrophobic. In other words, one end is lipophobic (hydrophilic) and another end is lipophilic (hydrophobic). When soap is dissolved in water and clothes are put in the soapy solution, soap molecules converge in a typical fashion to make a structure; called micelle. The hydrophobic ends of different molecules surround a particle of grease and make the micelle; which is a spherical structure. In this, the hydrophilic end is outside the sphere and hydrophobic end is towards the centre of the sphere. That is how, soap molecules wash away dirt and grease by making micelles around them.

Soap and Hard Water:

Hard water often contains salts of calcium and magnesium. Soap molecules react with the salts of calcium and magnesium and form a precipitate. This precipitate begins floating as an off-white layer over water. This layer is called scum. Soaps lose their cleansing property in hard water because of formation of scum. Detergents are used; instead of soaps; in hard water to overcome the problem. Detergents are usually ammonium or sulphonate salts of carboxylic acids. The charged ends of these compounds do not form precipitate with calcium or magnesium salts in hard water. Hence, detergents retain their cleansing property in hard water.