Plus One Chemistry Notes Chapter 12 Organic Chemistry: Some Basic Principles and Techniques is part of Plus One Chemistry Notes. Here we have given Kerala Plus One Chemistry Notes Chapter 12 Organic Chemistry: Some Basic Principles and Techniques.
|Text Book||NCERT Based|
|Chapter Name||Organic Chemistry: Some Basic Principles and Techniques|
|Category||Plus One Kerala|
Kerala Plus One Chemistry Notes Chapter 12 Organic Chemistry: Some Basic Principles and Techniques
The element carbon has the unique property called catenation due to which it forms covalent bonds with other carbon atoms. It also forms covalent bonds with atoms of other elements like hydrogen, oxygen, nitrogen, sulphur, phosphorus and halogens. The resulting compounds are studied under a separate branch of chemistry called organic chemistry.
Tetravalency of Carbon
Carbon can share four electrons with other atoms to form four covalent bonds. It is called tetravalency of carbon.
Shapes of Carbon or Organic Compounds
Carbon (ground state, z = 6) 1s2 2s2 2px1 2py1 has 2 unpaired electrons.
Carbon (excited state, z = 6) 1s2 2s2 2px1 2py1 2pz1 has 4 unpaired electrons.
The shape of
- Methane (CH4): Tetrahedral, sp3hybridisation.
- Ethene (C2H4): Triagonal, sp2 hybridisation.
- Ethyne (C2H2): Diagonal, sp hybridisation.
Note: Greater the s character of the hybrid orbitals, greater is the electronegativity.
Effect of Hybridisation on Bond Length and Bond Enthalpy
The bond length and bond strength depend upon hybridisation.
Structural Representations of Organic Compounds
Complete structural formula.
It focuses on the electrons involved in bond formation. A single dash represents a single bond, double dash is used for a double bond and triple dash represents a triple bond.
Condensed structural formula.
It focus on the number of identical group attached to an atom by a subscript or omitting some or all the dashes representing covalent bonds.
CH3CH2CH2CH2CH2CH2COOH – complete form
CH3(CH2)5COOH – condensed form
Bond line structure.
It focus on the lines rep-resenting carbon-carbon bonds are drawn in a zig-zag fashion.
Classification of Organic Compounds
Acyclic or Open Chain or Aliphatic Compounds.
This type of organic compounds consists of straight or branched chain compounds.
Alicyclic or Closed chain or Ring Compounds.
It contain carbon atoms joined in the form of a ring.
1. Homocyclic or carbocyclic compounds
The compounds in which the ring consists of only carbon atoms are called homocyclic compounds.
eg., cyclopropane, cyclobutane.
2. Alicyclic compounds (CnH2n)
The homocyclic compounds containing a ring of 3 or more carbon atoms which resembles with aliphatic compounds are called alicyclic compounds.
3. Aromatic compounds
These carbocyclic compounds contain at least one benzene ring (a ring of six carbon atoms with alternate double and single bond).
4. Heterocyclic compounds
The compounds in which the ring consists of atoms of more than one kind are called heterocyclic compounds. The atom other than that of carbon namely N, O or S present in the ring is called an hetero atom. They form 5 membered or 6 membered heterocyclic ring.
A functional group is an atom or group of atoms which determine the chemical behavior at an organic compound,
- -OH (alcohol)
- -CHO (aldehyde)
- -COOH (carboxylic acid)
The successive members differ from each other in molecular formula by a -CH2 unit is known as homologous series.
Give the IUPAC name of the following compound:
Write the structural formula of 4-chloro- 2-pentene.
The compounds having the same molecular formula (M.F) but different structural formula (S.F) or difference in physical and chemcial properties is known as Isomers, and the phenomenon is known as isomerism.
Compounds having same M.F, but different structural formula are called structural isomers.
Compounds having same M.F but they differ in the arrangement of carbon chain are called chain isomers. This type of isomerism is known as chain isomerism.
Position isomerism. This isomerism arises due to the difference in the position of the same functional group or same substituents on the chain.
The compounds having same MF but different functional groups are called functional isomers,
eg., C3H80 represents an ether and an alcohol.
It arises due to different alkyl chains on either side of the functional group in the molecule
Compounds having the same structural formula but different spatial arrangement of atoms or groups are called sterioisomerism.
A group of atoms in which carbon atom has six electron in its valence shell, out of which two electrons are unshared are called carbenes. Carbenes are reaction intermediates that contain uncharged or neutral species of divalent carbon. When two groups are eliminated from same carbon atom (or elimination) carbenes are formed.
Electrophiles or Electrophilic Reagent or Electron loving agent
Electrophile is a neutral molecule or positively charged ion containing an atom which is deficient in electrons. They can accept a pair of electron from substrate. It can act as Lewis acids and attack electron rich centres.
Positive electrophiles: H+, Cl+, H3O+, NO2+ etc.
Neutral electrophiles: AICI3, BF3 and free radicals, carbenes etc.
Nucleophiles or Nucleus loving Reagent
Nucleophile is a neutral or negatively charged species which can donate a pair of electrons to substrate. It can act as a Lewis base. It attacks electron deficient centres.
Negative nuclephiles: Cl–, OH–, ON–, NO2–, carbanion, RCOO
Neutral nucleophiles: NH3, H2O, ROH, RNH2
Explain the following giving example:
i. Inductive effect
i. Inductive effect: The permanent electron displacement along a chain due to the presence of a polar covalent bond is called inductive effect, e.g., electron withdrawing effect.
If an atom or group attracts electron less strongly than hydrogen it is said to have +1 effect electron releasing gloup ).
ii. Electrophile: It is positively charged or neutral species which is electron deficient,
e.g., H+, H30+, Cl+, CH3+are electrophiles.
Organic Reactions and Mechanisms
A reaction in which a H atom or other atom or group attached to carbon is replaced by another atom or a group.
A reaction in which atoms or groups are added to unsaturated alkenes or alkynes.
1. Alpha (α) elimination reaction.
The reaction in which the two atoms or groups are eliminated from the α-position giving an electron deficient reactive intermediate is called α elimination.
2. Beta (β) elimination
The reaction in which the two atoms or groups are eliminated from the adjacent α and β positions is called β elimination.
The reaction in which the products get formed by the rearrangement of atoms in the reacting molecule are termed as rearrangement reactions.
Methods of Purification of Organic compounds Sublimation
Certain substances on heating are converted into vapours without passing through the liquid state. The vapours on cooling yield crystals of pure solid compounds. Sublimation is used to separate sublimable compounds from non volatile impurities,
eg., Naphthalene, camphor.
Crystallisation is one of the most commonly used technique for the purification of solid organic compounds. It is based on the difference in the solubilities of the compounds and the impurities in a suitable solvent.
It is used to separate:
- Volatile liquids from non volatile impurities.
- The liquids having sufficient difference in their boiling points,
eg., chloroform (b,p:334K) and aniline (b.p: 457K).
This method is used when the boiling point of two liquids are close to each other. Fractional distillation is carried out by using a fractionating column.
This technique is used to separate substances which are steam volatile and are immiscible with water.
When an organic compound is present in an aqueous medium, it is separated by shaking it with an organic solvent in which it is more soluble than in water.
Chromatography is the method of identification, purification or separation of the components of a mixture containing, polar organic and inorganic compounds.
There are two types of chromatography. They are:
- Adsorption chromatography.
This type of chromatography is based on the principal of differential adsorption of various components of the mixture on a suitable adsorbent.
- Partition chromatography.
This chromatography is based on continuous differential partitioning (distribution) of components of a mixture between stationary and mobile phases.
eg., paper chromatography.
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