Class 11- Chemistry: Chapter 13: Hydrocarbons by Subhas C Chakra

 

Hydrocarbons

Hydrocarbon
A compound of carbon and hydrogen is known as hydrocarbon.
• Saturated Hydrocarbon
A hydrocarbon is said to be saturated if it contains only C—C single bonds.
For example: Ethane CH3—CH3 
• Unsaturated Hydrocarbon

• Aromatic Hydrocarbon
Benzene and its derivatives are called aromatic compounds.
Example:

• Alicyclic Compounds
Cyclic compounds which consist only of carbon atoms are called alicyclic or carboeyclic compounds.

• Heterocyclic Compounds
Cyclic compounds in which the ring atoms are of carbon and some other element (For example, N, S, or O) are called heterocyclic compounds.

• Alkanes
Alkanes are the simplest organic compounds made of carbon and hydrogen only.
They have the general formula CnHC2n+2 (where n = 1, 2, 3, etc.)
The carbon atoms in their molecules are bonded to each other by single covalent bonds. Since the carbon skeleton of alkanes is fully saturated’ with hydrogens, they are also called saturated hydrocarbons. Alkanes contain strong C —C and C —H bonds. Therefore, this class of hydrocarbons are relatively chemically inert. Hence they are sometimes referred to as paraffins (Latin parum affinis = little affinity). First three members of this class can be represented as

Structure:

In methane carbon forms single bonds with four hydrogen atoms. All H—G—H bond angles are of 109.5°. Methane has a tetrahedral structure. C—C and C—H bonds are formed by head-on overlapping of sp3 hybrid orbitals of carbon and Is orbitals of hydrogen atoms.
• Nomenclature Guidelines
Use the following step-by-step procedure to write the IUPAC names from the structural formulas. Consider the following structural formula:

Step 1. Identify the longest chain: In the given example, longest chain has seven carbons. The seven carbon chain is heptane.

Step 2. Number the chain: The chain is numbered from left to right. This gives lowest numbers to the attached alkyl group.
Step 3. Identify the alkyl group: There are two methyl groups at C-2 and C-3, there is one ethyl group of C-4.
Step 4. Write the IUPAC name: In this case the IUPAC name is 4-Ethyl-2,3-dimethyl heptane. Always keep in mind (a) Numbers are separated from each other by commas. (b) Numbers are separated from names by hyphens, (c) Prefixes di, tri are not taken into account in alphabetising substituent names.
• Newman Projections
In this projection, the molecule is viewed at the C—C bond head on.

• Relative Stability of Conformations
In staggered form of ethane there are maximum repulsive forces, minimum energy and maximum stability of molecule. On the other hand, when the staggered form changes in the eclipsed form the electron clouds of the carbon hydrogen bonds come closer to each other resulting in increase in electron cloud repulsions, molecule have to possess more energy and thus has lower stability.
Torsional Angle: Magnitude of torsional strain depends upon the angle of rotation about C—C bond. This angle is also called dihedral angle or torsional angle.
• Alkenes
Alkenes are hydrocarbons that contain a carbon-carbon double bond (C=C) in their molecule.
They have the general formula
Structure:
Let us consider (H2C=CH2) for illustrating the orbital make up of alkenes.
In ethylene the carbon atoms are sp2 hybridized- They are attached to each other by a a bond and a σ bond.
The a bond results from the overlap of two sp2 hybrid orbitals. The π bond is formed from overlap of the unhybridized p-orbitals. Ethylene is a planar molecule.

Ppints to be noted
(i) The carbon-carbon double bond in alkenes is made up of one σ and one π-bond.
(ii) Alkenes are more reactive than Alkanes. This is due to the availability of n electrons.
• Nomenclature
In IUPAC system
(i) The name of the hydrocarbon is based on the parent alkene having the longest ‘ carbon chain of which double bond is apart.
(ii) This chain is numbered from the end near the double bond and its position is indicated by the number of the carbon atom not which the double bond originates,
(iii) The name of the parent alkene with the position number of the double bond is written first and then the names of other substituents prefixed to it.

(iv) When there are two or three double bonds in a molecule, the ending-one of the corresponding alkane is replaced by-a diene to get the name.

• Isomerism
Structural Isomerism: Ethene and propene have no structural isomers, but there are three structures of butenes.

Of these, two are straight chain structures with the difference being in the position of double bond in the molecules.
These are position isomers and third structure is a branched-chain isomer.
Geometrical Isomerism: It is known that a carbon-carbon double bond is made up of one σ bond and one π-bond. The π-bond presents free rotation about the double bond.
This presentation of rotation about the carbon-carbon double bond gives rise to the phenomenon of geometrical isomerism. An alkene having a formula RCH=CHR can have two stereoisomers, depending upon whether the two alkyl groups are on the same or opposite sides of the double bond. If they are on the same side, then it is called cis-isomer. If they are on opposite sides, then it is called trans-isomer.
Due to different arrangement of atoms or groups in space, these isomers differ in their properties like melting point, boiling point, dipole moment, solubility, etc.

• Alkynes
Alkynes are characterised by the presence of a triple bond in the molecule.
Their general formula is CnH2n-2.
The first and the most important member of this series of hydrocarbons is acetylene, HC=CH, and hence they are also called the Acetylenes.
Structure: Let us consider ethyne (HC=CH) for illustrating the orbital make up of ethyne. In ethyne, the carbon atoms are sp hybridized. They are attached to each other by a σ-bond and two π-bonds.
The σ -bond results from the overlap of two sp hybrid orbitals. The π bonds are formed from the separate overlap of the two p-orbitals from the two adjacent carbon atoms.
The other sp hybrid orbital of each carbon atom forms a σ bond with another carbon or hydrogen atom. Ethyne is a linear molecule.

Points to be noted:
(i) The carbon-carbon triple bond in alkynes is made up of one σ and two π bonds.
(ii) Like alkenes, alkynes undergo addition reaction. These reactions are due to the availability of more exposed π electrons.
• Nomenclature
IUPAC System: The IUPAC names of alkynes are obtained by dropping the ending-ane of the parent alkane and adding the suffix-yne. Carbon chain including the triple bond is – numbered from the end nearest this bond. The position of the triple bond is indicated by prefixing the number of carbon preceding it to the name of the alkyne.

Preparation:
From calcium carbide: Ethyne is prepared by treating calcium carbide with water. Calcium carbide is prepared as follows:

From vicinal dihalides: When reacted with vicinal dihalides, alcoholic potassium hydroxide undergo dehydrohalogenation. One molecule of hydrogen halide is eliminated to form alkenyl halide which on treatment with sodamide gives alkyne.

• Aromatic Hydrocarbons
These hydrocarbons are also known as ‘arenes’. Most of such compounds were found to contain benzene ring.
Aromatic compounds containing benzene ring are known as benzenoids and those not containing a benzene ring are known as non-benzenoids. Some examples of arenes are given below.

Nomenclature and Isomerism: Benzene and its homologous are generally called by their common names which are accepted by the IUPAC system. The homologous of benzene having a single alkyl group are named as Alkyl benzenes.

Structure of Benzene: By elemental analysis, it is found that molecular formula of benzene is C6H6. This indicates that benzene is a highly unsaturated compound. In 1865, Kekule gave the cyclic planar structure of benzene with six carbons with alternate double and single bonds.

The Kekule structure indicates the possibility of two isomeric 1,2-dibromobenzenes. In one of the isomers, the bromine atoms are attached to the doubly bonded carbon atoms whereas in the other they are attached to the singly bonded carbon.

In fact, only one ortho-dibromobenzene could be prepared.
To overcome this problem Kekule suggested that benzene was a mixture of two forms.

Failure of Kekule’s structure: Kekule structure of benzene failed to explain the unique stability and its preference to substitution reaction than addition reactions.
Resonance Structure of Benzene: The phenomenon in which two or more structures can be written for a substance which involve identical positions of atoms is called resonance. In benzene’s Kekule’s structures (1) and (2) represent the resonance structures. Actual structure – of the molecule is represented by hybrid of the these two structures.

Orbital structure of benzene: All six carbon atoms in benzene are sp2 hybridized. The sp2 hybrid orbitals overlap with each other and with s orbitals of the six hydrogen atoms forming C—C and C—H σ-bonds.

X-Ray diffraction data indicates that benzene is a planar molecule. The data indicates that all the six C—C bond length are of the same order (139 pm) which is intermediate between (C—C) single bond (154 pm) and C—C double bond (133 pm). Thus the presence of pure double bond in benzene gives the idea of reductance of benzene to show addition reaction under normal condition. The is, It explains the unusual behaviour of benzene.
Aromaticity: It is a property of the sp2 hybridized planar rings in which the p orbitals allow cyclic delocalization of π electrons.
Conditions for Aromaticity:
(i) An aromatic compound is cyclic and planar.
(ii) Each atom in an aromatic ring has a p orbital. These p orbitals must be parallel so that a continuous overlap is possible around the ring.
(iii) The cyclic π molecular orbital (electron cloud) formed by overlap of p orbitals must contain (4n + 2) π electrons. Where n = integer (0, 1, 2, 3, etc.). This is known as Huckel rule.
Some Examples of Atomic Compounds are given below:


Preparation of Benzene: Benzene is commercially isolated from coaltar. However, there are some synthetic methods which is applied in the laboratory for the preparation of benzene.

Physical Properties of Benzene:
(i) Benzene is a colourless liquid.
(ii) It is’ insoluble in water. It is soluble in alcohol, ether, chloroform etc.
(iii) Benzene itself is a good solvent for many organic and inorganic substances e.g., fat, resins, sulphur and iodine.
(iv) It bums with a luminous, sooty flame in contrast to alkanes and alkenes which usually bum with a bluish flame.
Chemical Properties:
Benzene undergeos following types of chemical reactions.
(i) Electrophillic Substitution Reaction
(ii) Addition Reaction
Electrophillic Substitution Reactions:


Benzene on treatment with excess of chlorine in the presence of anhydrous AlCl3 can be chlorinated to hexachlorobenzene (C6Cl6)

Mechanism of electrophilic substitution reactions:
All electrophilic substitution reactions follow the same three step mechanism.
Setp 1. Formation of an electrophile:

Step 2. The electrophile attacks the aromatic ring to form a carbonium ion.

Step 3. Loss of proton gives the substitution product.
Activating groups: These group activates the benzene ring for the attack by an electrophile. Example, —OH; —NH2, —NHR, —NHCOCH3, —OCH3 —CH3 —C2H5 etc.
Deactivating groups: Due to deactivating group because of strong —I effect, overall electron density on benzene ring decreases. It makes further substitution difficult.
Metadirecting group: The groups which direct the incoming group to meta position are called meta directing groups. Some examples of meta directing groups are —N02, —CN, —CHO, —COR, —COOH, —COOR, -S03H etc.
Let us consider the example of nitro group: Since Nitro group due to its strong -I effect reduces the electron density in benzene ring. Nitrobenzene is a resonance hybrid of following structures.

Carcinogenicity and Toxicity: Some polynuclear hydrocarbons containing more than two benzene rings fused together become toxic and they are having cancer producing property. They are actually formed due to incomplete combustion of some organic materials like tobacco, coal and petroleum, etc.
Some of the carcinogenic hydrocarbons are given below.

• Hydrocarbons: They are compounds of carbon and hydrogen only.
Open Chain saturated compound—Alkane
Unsaturated Compound—Alkenes and Alkynes Aromatic Compound—Benzene and its derivatives Terminal alkynes are weakly acidic in nature.
• Conformation: Spatial arrangements obtained by rotation around sigma bonds.
• Eclipsed Conformation: Less stable because of more repulsion between bond pairs of electrons.
• Staggered: It is more stable since there is less repulsion between bond pairs of electrons.
• Geometrical isomerism: Observed only in compounds containing a double bond.
• Stability of benzene. Is explained on the basis of resonance hybrid.
• Arenes: Take part in electrophilic substitution reaction.
Aromaticity is determined by Huckle’s rule (4n + 2) rule

Class 11- Chemistry: Chapter 12: Organic Chemistry Some Basic Principles and Techniques by Subhas C Chakra

 

Organic Chemistry: Some Basic Principles and Techniques

Organic Chemistry
Organic chemistry is the branch of chemistry that deals with the study of hydrocarbons and their derivatives.
The Shapes of Carbon Compounds:
In organic or carbon compounds, s and p orbitals are involved in hybridisation. This leads to y three types of hybridisation which are sp3(in alkanes) – Tetrahedral in shape sp2(in alkenes) – Planar structure sp(in alkynes) – Linear molecule
Functional Group: The functional group are atom or group of atoms joined in a specific manner which determines the chemical properties of the organic compound. The examples are hydroxyl group (—OH), aldehyde group (—CHO) and carboxylic acid group (—COOH) etc.

• Homologous Series
A homologous series may be defined as a family of organic compounds having the same functional group, similar chemical properties and the successive members differ from each other in molecular formula by —CH2 units.
The members of a homologous series can be represented by same general molecular formula.
• Nomenclature of Organic Compounds
Common name (Common system): Before the IUPAC system of nomenclature, organic compounds were named after the sources of origin, for example, urea was so named because it was obtained from the urine of mammals. Formic acid was so named since it was extracted from red ants called formica.

• I UP AC (International Union of Pure and Applied Chemistry) System
According to IUPAC system, the name of an organic compound contains three parts: (i) word root, (ii) suffix, (iii) prefix.
(i) Word root: Word root represents the number of carbon atoms present in the principal chain, which is the longest possible chain of carbon atoms.

(ii) Suffix: Suffix are of two types, primary suffix, secondary suffix.
(a) Primary Suffix: It indicates the type of bond in the carbon atoms.

(b) Secondary Suffix: Secondary suffix is used to represent the functional group.
(iii) Prefix: Prefix is a part of IUPAC name which appears before the word root. Prefix
are of two types:
(a) Primary prefix: For example, primary prefix cyclo is used to differentiate cyclic compounds.

(b) Secondary prefix: Some functional groups are considered as substituents and denoted by secondary prefixes.
For example:
Substituted Group            Secondary prefix.
— F                                           Flupro
— Cl                                         Chloro
— Br                                        Bromo
— NO                                      Nitroso
— NO2                                              Nitro
— CH3                                    Methyl
— OCH3                                Methoxy
Naming of Compounds Containing Functional Groups: The longest chain of carbon atoms containing the functional group is numbered in such a manner that the functional group is attached at the carbon atoms possessing lowest possible number in the chain.
In case of polyfunctional compounds, one of the functional group is selected as principal functional group and the compound is named on that basis. The choice of principal functional group is made on the basis of order of preference.
The order of decreasing priority for the functional group is

• Isomerism
When there are two or more compounds possessing the same molecular formula but different structural formula and different physical and chemical properties, the phenomenon is called isomerism. Such compounds are called isomers.
It is of two types:
(1) Structural Isomerism
(2) Stereoisomerism
(1) Structural Isomerism: Structural isomerism is shown by compounds having the same molecular formula but different structural formulae differing in the arrangement of atoms.
(2) Stereoisomerism: When isomerism is caused by the different arrangements of atoms or groups in space, the phenomenon is called stereoisomerism. The steroeoisomers have same structural formula but differ in arrangement of atoms in space. Stereoisomerism is of two types:
(i) Geometrical or Cis-Trans Isomerism
(ii) Optical Isomerism
• Fundamental Concepts in Organic Reaction Mechanism
Fission of a covalent bond: A covalent bond can undergo Fission in two ways:
(i) By Homolytic Fission or Homolysis
(ii) By Heterolytic Fission or Heterolysis
Homolytic Fission: In this process each of the atoms acquires one of the bonding electrons.

Heterolytic Fission: In this process one of atoms aquires both of the bonding electrons when the bond is broken.
If B is more electronegative than A which thereby aquires both the bonding electrons and becomes negatively charged.

The products of heterolytic fission are ions.
Reaction Intermediates: Heterolytic and homolytic bond fission results in the formation of short-lived fragments called reaction intermediates. Among the important reaction intermediates are carbonium ions, carbanions, carbon free radicals and carbenes. Carbonium Ions (carbocations): Organic ions which contain a positively charged carbon atom are called carbonium ions or carbocations. They are formed by heterolytic bond fission.

where Z is more electronegative than carbon.
Tertiary carbonium ion is more stable than a secondary, which in turn is more stable than a primary because of +1 effect associated with alkyl group.

Carbanion: Organic ion which contains a negatively charged carbon atom are called carbanions. They are also formed by heterolytic bond fission.

Where Z is less electronegative than carbon. A primary carbanion is more stable than a secondary, which in turn is more stable than a tertiary, because of +1 effect associated with alkyl group.

Electrophile: It is positively charged or neutral species which is electron deficient, e.g.,
He–, H20+, CH3 , NH4+, AICl3 , S03 , CHCl2 , CCI3.
Nucleophile: It is negatively charged or neutral species with lone pair of electrons e.g., (HO–), Cyanide (C = N), H20: R3N, R2NH etc.
Electron Displacement Effects in Covalent Bonds: Electronic displacements in covalent bonds occurs due to the presence of an atom or group of different electronegativity or under the influence of some outside attaching group.
These lead to a number of effects which are as follows:
(i) Inductive effect (ii) Elecromeric effect
(iii) Resonance or Mesomeric effect (iv) Hyperconjugation effect.
Inductive Effect: It involues c electron. The a electrons which form a covalent bond are seldom shared equally between the two atoms. Due to different electronegatively electrons are displaced towards the more electronegative atom.
This introduces a certain degree of polarity in the bond.
The more electronegative atom acquires a small negative charge (δ–). The less electronegative atom acquires a small positive charge (δ+).
Consider the carbon-chlorine bond
As chlorine is more electronegative, it will become negatively charged with respect to the carbon atom.

Structure I- indicates the relative charges on the two atoms.
Structure II- indicates the direction in which the electrons are drawn.
Atoms or groups which lose electrons towards a carbon atom are said to have a +1 effect. Those atoms or groups which draw electrons away from a carbon atom are said to have a -I Effect.
Some common atoms or groups which cause +I or -I effects are shown below:

The inductive effect of C3 upon C2 is significantly less than the effect of the chlorine atom on C.
Resonance Structure: A number of organic compounds cannot be accurately represented by one structure.
For example, benzene is ordinarily represented as

Carbon-carbon double bond length = 1.34 A
Carbon-carbon single bond length = 1.54A. But it has been determined experimentally that all carbon-carbon bonds in benzene are identical and have same bond length (1.39A).
Thus the structure of benzene cannot be represented by single structure. It can be represented equally well by ‘he energetically similar structures I and II. The two structures are called resonance structures.

Actual structure of benzene is resonance hybrid of structures I and II.
Another example of resonance is provided by nitromethane (CH3N02) which can be represented by two Lewis structures.

The actual structure of nitromethane is a resonance hybrid of the two canonical forms I and II. Resonance energy: The difference in the energy between the most stable contributing structure for a compound and its resonance hybrid is called as resonance energy or resonance stabilisation energy.
Resonance Effect: The polarity produced in the molecule by the interaction of two π-bonds or between a π-bond and a lone pair of electrons present on an adjacent atom. There are two types of resonance or mesomeric effects designated as R or M effect.
Positive Resonance Effect (+R effect):
Those atoms which lose electrons towards a carbon atom are said to have a +M effect or +R effect. For example:
—Cl, —Br, —I, —NH2, —NR2, —OH, —OCH3
Negative Resonance Effect (-R effect): Those atoms or groups which draw electrons away from a carbon atom are said to have a -M effect or -R effect.
For example:

Electromeric Effect (E Effect):
The electrom’eric effect refers to the polarity produced in a multiple bonded compound when it is attacked by a reagent when a double or a triple bond is exposed to an attack by an electrophile E+ (a reagent) the two π electrons which from the π bond are completely transferred to one atom or the other. The electromeric effect is represented as:

The curved arrow shows the displacement of the electron pair. The atom A has lost its share in the electron pair and B has gained this share. Therefore A acquires a positive charge and B a negative charge.

Hyperconjugation or No Bond Resonance: When the alkyl group is attached to an unsaturated system such as —CH=CH2 group the order of inductive effect gets reversed. The behaviour can be explained by hyperconjugation effect.
Such structures are arrived at by shifting the bonding electrons from an adjacent C —H bond to the electron deficient carbon. In this way, the positive charge originally on carbon is dispersed to the hydrogen.
This way of electron release by assuming no bond character in the adjacent C—H bond is called No-Bond Resonance or Hyperconjugation.

• Orbital Concept of Hyperconjugation
It involues delocalisation of o electrons of C—H bond of an alkyl group which is attached directly to an atom of unsaturated system or to an atom with an unshared p-orbital.
Let us consider CH3CH2 (ethyl cation) in which the positively charged carbon atom has an empty p-orbital. One of the C—H bonds of the methyl group can align in the plane of this empty p-orbital and electron constituting the C—H bond in plane with this p-orbital can then be delocalised into the empty p-orbital as in Fig.

In general, greater the number of alkyl groups attached to a positively charged carbon atom, the greater is the hyperconjugation.

• Qualitative Analysis of Organic Compounds
Detection of Carbon and hydrogen: Put Copper Oxide Test:
The organic substance is mixed intimately with about three times its weight of dry copper oxide. The mixture is then placed in a hard glass test-tube fitted with a bent delivery tube. The other end of which is dipping into lime water in another test tube.
The mixture is heated strongly and the following reactions take place.

Thus if carbon is present it is oxidised to carbon dioxide which turns lime water milky. If hydrogen is also present, it will be oxidised to water droplets on the cooler wall of the test tube.
Detection of other elements
Lassaigne’s test: Nitrogen, sulphur, halogens and phosphorus present in an organic compound are detected by ‘Lassaigne’s test’. Covalent compounds are converted into ionic form by fusing the compound with sodium metal. Following reaction occurs:

Test for Nitrogen:
(i) The substance is heated strongly with sodium metal.
Na + C + N ———–> NaCN
(ii) The water extract of the fused mass is boiled with ferrous sulphate solution

(iii) To the cooled solution is then added a little ferric choride solution and excess of concentrated hydrochloric acid.

The formation of prussian blue or green colouration confirms the presence of nitrogen.
Test for sulphur:
Sodium Test: Sulphur, if present, in the given organic compound, upon fusion with sodium reacts to form sodium sulphide

Thus the sodium extract obtained from the fused mass is tested as:
(i) Add freshly prepared sodium nitroprusside solution. A deep violet colouration indicates sulphur.
(ii) Acidify the portion of the extract with acetic acid and then add lead acetate solution. A black precipitate of lead sulphide confirms the presence of sulphur.

If nitrogen and sulphur both are present in an organic compound, sodium thiocyanate is formed. It gives blood red colour and no prussian blue since there are no free cyanide ions.

Test for Halogens
Sodium Test: Upon fusion with sodium, the halogens in the organic compound are converted to sodium halides.
Cl + Na ——-> NaCl
Br + Na ———> NaBr
I + Na ———>NaI
Acidify a portion of ‘sodium extract’ with dilute nitric acid and add to it silver nitrate solution. White ppt. soluble in ammonia indicates Chlorine.
Yellow ppt. sparingly soluble in ammonia indicates Bromine.
Yellow ppt. insoluble in ammonia indicates Iodine.
When nitrogen or sulphur is also present in the compound, the sodium extract before testing for halogens is boiled with strong nitric acid to decompose the cyanide and the sulphite formed during the sodium fusion. If not removed, these radicals will form a white and black precipitate respectively on the addition of silver nitrate.

Test for phosphorous
The compound is heated with an oxidising agent (sodium peroxide). The phosphorous present in the compound is oxidised to phosphate.
The solution is boiled with HN03 and treated with ammonium molybdate. A yellow coloured ppt. indicates the presence of phosphorous.

• Quantitative Analysis
Estimation of Carbon and Hydrogen
Both carbon and hydrogen are estimated together in one operation. A known weight of an organic compound is burnt in the presence of excess of oxygen and copper (II) oxide. Carbon and hydrogen are oxidised to carbon dioxide and water respectively.

The weight of carbon dioxide and water thus formed are determined and the amounts of carbon and hydrogen in the original substance calculated.

Estimation of Nitrogen
(i) Dumas method: This method is based on fact that the nitrogenous compounds when heated with copper oxide in an atmosphere of carbon dioxide yield free nitrogen,

The traces of oxides of nitrogen, which may be formed in some cases, are reduced to elemental nitrogen by passing over heated copper spiral.
Apparatus can be shown as:

(ii) Kjeldahl’s Methods: Kjeldahl’s method is based on the fact that when an organic compound containing nitrogen is heated with con. H2S04 the nitrogen in it is converted to ammonium sulphate. The resultant liquid is then treated with excess of alkali and the liberated ammonia gas absorbed in excess of standard acid. The amount of ammonia is determined by finding the amount of acid neutralised by back filtration with some std. alkali.

• All organic compounds contain carbon and hydrogen as essential constituents.
• In a homologous series two successive members differ in their molecular formula by -CH2 unit.
• Aliphatic Compounds are open chain compounds contain straight or branched chain of carbon atoms.
• Alicyclic Compounds: Compounds containing closed ring of carbon compounds.
• Aromatic Compounds: Benzene and its derivatives are called aromatic compounds.
• Functional group: A functional group is an atom or group of atoms bonded together in a unique fashion and which determines the physical and chemical properties of the compounds.
• Homolytic Bond Fission: It leads to the formation of free radicals.

• Crystallisation is used to purify organic solids by dissolving them in suitable solvents.
• Simple distillation is used to purify liquids with non-volatile impurities.
• Steam distillation is used to purify organic compounds which give sufficient vapours at the boiling of water and are insoluble in water.
• Chromatography is used to purify and separate the constituents from a sample.
• Lassaigne’s test is used to detect carbon, nitrogen, sulphur and halogen in organic compound.
• Dumas or Kjeldahl’s method: Nitrogen is estimated by this method.
• Halogens: Halogens are estimated by Carius method.
• Sulphur and phosphorous: Sulphur and phosphorous are estimated by oxidising them to sulphuric and phosphoric acid respectively.
• Oxygen: The percentage of oxygen is usually determined by difference between the total percentage (100) and the sum of the percentages of all other elements present.