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General Organic Chemistry Class 11 Notes Chemistry

Bond Fission:
(a) Homolytic fission: Each atom separates with one electron, leading to the formation of highly reactive entities called radicals, owing their reactivity to their unpaired electron.
(b) Heterolytic fission: One atom holds on to electrons, leaving none for the other, the result in the above case being a negative and positive ion, respectively, the result being the formation of an ion pair.
Reactions involving radicals tend to occur in the gas phase and in solution in non-polar solvents, and to be catalyzed by light and by the addition of other radicals.  Reactions involving ionic intermediates take place more readily in solution in polar solvents, because of the greater ease of separation of charges therein and very often because of the stabilization of the resultant ion pairs through solvation.

Electronic Displacement in Covalent Bonds
The following four types of electronic effects operates in covalent bonds
(a) Inductive effect
(b) Mesomeric and Resonance effect
(c) Electromeric effects
(d) Hyperconjugation
General Organic Chemistry Class 11 Notes Chemistry

Inductive Effect:
(a) Negative inductive Effect: (–I Effect):This is due to electron - attracting groups (X); it develops positive charge on the chain and is said to exert a negative inductive denoted by (– I)
General Organic Chemistry Class 11 Notes Chemistry
(1) It decreases as one goes away from group X (electron attracting): X-C1-C2-C3
C1(d+) > C2(dd+) > C3(ddd+) and after third carbon charge is negligible

D and L configuration:
(a) The configuration of an enantiomer is related to a standard, glyceraldehydes.
Order:  +NH3NO2 > F > COOH > Cl > Br > I > OH > C6H5
(b) Positive Inductive Effect (+I): This is due to electron-releasing group (Y). It develops an negative charge on the chain and is said to exert a positive inductive effect denoted by (+I)
General Organic Chemistry Class 11 Notes Chemistry
(1) It also decreases as we go away group Y (electron - releasing):Y-C1-C2-C3
C1(d–) > C2(dd–) > C3(ddd–)
(2) Order: (CH3)3 C -R > (CH3)2CH-R > CH3CH2-R > CH3-R

 
(–I) effect
(+I) Effect
Acidic nature –
Increases
Decreases
Basic nature–
Decreases
Increases


Mesomeric Effect or Resonance Effect:
In conjugated systems, p-electrons shifting takes place consecutively giving permanent polarity on the chain.  
(a) Positive Mesomeric Effect (+M):  A group or atom is said to have +M effect when
the direction of electron -displacement is away from it.
General Organic Chemistry Class 11 Notes Chemistry
This effect extends the degree of delocalization and imparts stability to the molecule
General Organic Chemistry Class 11 Notes Chemistry
General Organic Chemistry Class 11 Notes Chemistry
(b) Negative Mesomeric Effect (–M): A group or atom is said to have +M effect when the direction of electron -displacement is toward it.
General Organic Chemistry Class 11 Notes Chemistry
(c) Resonance Energy: The difference in energy between the hybrid and the most stable canonical structure is  called as Resonance energy
General Organic Chemistry Class 11 Notes Chemistry


Electromeric Effect: 
Complete transfer of p-electrons from one atom to other to produce temporary polarity on atoms joined by multiple bonds, in the presence of an electrophile is known as electromeric effect. Effect is reversible and temporary.
(a)  Positive Electromeric Effect:
p-electrons transfer takes place C to C (as alkenes, alkynes etc.)
General Organic Chemistry Class 11 Notes Chemistry
(b) Negative Electromeric Effect:
p-electrons transfer takes place to more electronegative atom (O,N,S) joined by multiple bonds.
General Organic Chemistry Class 11 Notes Chemistry
General Organic Chemistry Class 11 Notes Chemistry


Hyperconjugation:
Delocalization of sigma electrons also known as sigma-pi – conjugation or no bond resonance.
It is a permanent effect.
(a) Occurrence
Alkene, alkynes
Free radicals (saturated type)  carbonium ions (saturated type)
(b) Condition
Presence of a–H with respect to double bond, triple bond carbon containing positive charge (in carbonium ion) or unpaired electron (in free radicals)
Example
General Organic Chemistry Class 11 Notes Chemistry
Note: Number of hyperconjugative structures = number of a-Hydrogen. Hence, in above examples structures I,ii,iii,iv are hyperconjugate structures (H-structures).
(c) Effects of Hyperconjugation:
Bond Length: Hyperconjugation also affects bond lengths because during the process the single bond in compound acquires some double bond character and vice-versa
Dipole moment: Since hyperconjugation causes this development of charges, it also affects the dipole moment of the molecule.

Stability of carbonium Ions: Tertiary > Secondary > Primary
Stability of Free radicals:
General Organic Chemistry Class 11 Notes Chemistry

Reactive Intermediates:


 
Species
 
Geometry
 
Stability
 
 
Carbocation
 
sp2 hybridized with a planar structure and bond angles are of about 120°.
 There is a vacant unhybridized p orbital which (e.g. in the case of CH3+) lies perpendicular to the plane of C—H bonds
Any structural feature which tends to reduce the electron deficiency at the tricoordinate carbon stabilizes the carbocation 
Order: 3°> 2° > 1° > CH3+
 
Carbanions
sp3 hybridized with the unshared pair occupying one apex of the tetrahedron.
Pyramidal structures similar to those of amines.
Any structural feature which tends to reduce the electron deficiency at the tricoordinate carbon stabilizes the carbocation
Order: 3°< 2° < 1° < CH3-
 
Free Radicals
sp2 hybridized  with planar (trigonal) structure..
and
sp3 hybridized  with pyramidal structure.
Hyperconjugation increases the stability of free radical.
Order: : 3°> 2° > 1°


Isomerism:
General Organic Chemistry Class 11 Notes Chemistry


Structural Isomerism:

Isomerims
Description
Example
Chain Isomerism
This type of isomerism arises from the difference in the structure of carbon chain which forms the nucleus of the molecule.
Butane and Isobutane
Position Isomerism
It is the type of isomerism in which the compounds possessing same molecular formula differ in their properties due to the difference in the position of either the functional group or the multiple bond or the branched chain attached to the main carbon chain.
n-propyl alcohol and isopropyl alcohol
Functional Isomerism
In this type of isomerism two compounds have the same molecular formula but possess different functional groups.
Diethyl ether(C2H5-O-C2H5) and butyl alcohol (C4H9OH)
Metamerism
This type of isomerism is due to the unequal distribution of carbon atoms on either side of the functional group in the molecule of compounds belonging to the same class
For example, methyl propyl ether and diethyl ether both have the molecular
 
Tautomerism
It is the type of isomerism in which two functional isomers exist together in equilibrium. The two forms existing in equilibrium are called as tautomers.
Acetoacetic ester has two tautomers – one has a keto group and other has an enol group


Geometrical Isomerism:
The isomers possess the same structural formula containing a double bond and differ only in respect of the arrangement of atoms or groups about the double bond.
This isomerism is shown by alkenes or their derivatives in which two different atoms or groups are attached to each carbon containing the double bond.
Thus the compounds having the formula abC = Cxy or the simple structure abC = Cab occur in two forms and exhibit geometrical isomerism.
General Organic Chemistry Class 11 Notes ChemistryGeneral Organic Chemistry Class 11 Notes Chemistry
(a)The trans isomers of alkenes are usually more stable than their corresponding cis isomers.
(b) The trans isomers have normally less dipole moments than their corresponding cis isomers.
(c) The trans isomer has greater symmetry than the corresponding cis isomer. Thus it packs more easily in the crystal lattice and hence has higher melting points.

Optical Isomerism:
(a) Optical Activity: The property of a substance of rotating the plane of polarized light.
(b) Specific Rotation: The number of degrees of rotation observed when light is passed through 1 decimeter (10 centimeters) of its solution having concentration 1 gram per milliliter.
General Organic Chemistry Class 11 Notes Chemistry
(a) Laevorotatory or (-) - form:  rotates the plane of polarized light to the left.
(b) Dextrorotatory or (+)- form : rotates the plane of polarized light to the right.
(c) Racimic Mixture or (±)– mixture : An inactive from which does not rotate the plane of polarized light at all. This is a mixture of equal amounts of (+)– and (–)– forms and hence its optical inactivity
Asymmetric Carbon atom: A carbon atom which is attached to four different atoms

Chirality:
(a) All organic compounds which contain an asymmetric carbon (C* abde) atom are chiral and exist in two tetrahedral forms.
(b) A molecule must have chirality in order to show optical activity.
Enantiomers: Two optical isomers which are non superimposable mirror images of each other.
General Organic Chemistry Class 11 Notes Chemistry
(a) Meso compounds:  Compound containing two or more chiral carbon which do not show optical activity due to presence of centre of symmetry (indicated by thick dot).
(b) Compounds which have unsymmetrical molecule with one or more chiral centres: In such compounds if ’n’ is the number of chiral carbons, then
No. of optically active isomers (a) = 2n
No. of racemic forms (r) = a/2
No. of meso forms (m) = 0
(c) compounds having a symmetrical molecule (compounds having chiral carbons but molecule as a whole is achiral): (a) compounds with even number of carbons atoms: In such compounds if number of chiral carbons in n, we have a  = 2n–1, r = a/2, and  m=2(n/2-1)
(d) Compounds with odd number of carbon atoms: In such compounds if n is the number of asymmetric carbons then total optical isomers are given by 2n-1 whereas  m = 2(n-2)/2). Thus, a  = 2n–1 –2(n-1)/2).
General Organic Chemistry Class 11 Notes Chemistry
The force of rotation due to one half of the molecule is balanced by the opposite and equal force due to the other half. The optical inactivity so produced is said to be due to internal compensation. It occurs whenever a compound containing two or more

Fischer Projections:
(a) Representing three dimensional structures on a two dimensional surface.
(b) Asymmetric carbon atom drawn in a prescribed orientation and then projected into a planar surface.
(c) Planar formulas of the asymmetric carbon are obtained by placing it so that the two substituents are horizontal and project out towards the viewer (shown by thick wedge-like bonds), while the two other substituents are vertical and project away from the viewer (shown by dotted bonds).
General Organic Chemistry Class 11 Notes Chemistry

D and L configuration:
a) The configuration of an enantiomer is related to a standard, glyceraldehydes.
General Organic Chemistry Class 11 Notes Chemistry 
General Organic Chemistry Class 11 Notes Chemistry
(b) If the configuration at the asymmetric carbon atom of a compound can be related to D (+)-glyceraldehyde, it belongs to D-series.
(c) By convention for sugars, the configuration of the highest numbered asymmetric carbon is referred to glyceraldehyde to determine the overall configuration of the molecule.

R and S System:
The sequence rules to determine the order of priorities of groups are :
The atoms or groups directly bonded to the asymmetric carbon are arranged in order of decreasing atomic number and assigned priority 1, 2, 3, 4, accordingly
(a) Thus in chlorobromofluoromethane (CHClBrF), the substituents Br (at no = 35), Cl     (at no = 17), F (at no = 9) and H (at no = 1) give the order of priorities.
General Organic Chemistry Class 11 Notes Chemistry
(b) When two or more groups have identical first atoms attached to asymmetric     carbon, the priority order is determined by considering the atomic numbers of the   second atoms; and if the second atoms are also identical the third atoms along the chain are examined.
(c). If the first atoms of the two groups have same substituents of higher atomic number, the one with more substituents takes priority.
Thus ––CHCl2 has a higher priority than ––CH2­Cl.
(d) A doubly or triply bonded atom 'A' present in a group appended to asymmetric carbon, is considered equivalent to two or three singly bonded 'A's, respectively. Thus, R= A equals A-R-A.
If in a molecule, order of priority for groups a,b,c,d, & e is  a > b > d > e
General Organic Chemistry Class 11 Notes Chemistry

Diastereomers :

  • Stereoisomers which are optically active isomers but not mirror images, are called diasteriomers.
  • Diastereoisomers have different physical properties. Thus they have different melting points, boiling points, solubilities in a given solvent, densities, and refractive indices.
  • They also differ in specific rotations; they may have the same or opposite signs of rotations.
  • Like geometrical isomers, the diastereoisomers may be separated from each other :–
    • by fractional distillation due to their difference in boiling points;
    • by fractional crystallisation due to their difference in solubility;
    • by chromatography due to their different molecular shapes and polarity.
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FAQs on General Organic Chemistry Class 11 Notes Chemistry

1. What is organic chemistry?
Ans. Organic chemistry is the branch of chemistry that deals with the study of carbon compounds, including their structure, properties, composition, reactions, and synthesis. It focuses on the chemistry of compounds that contain carbon-hydrogen bonds.
2. What are the main types of organic reactions?
Ans. Organic reactions can be broadly categorized into several types. Some common types include substitution reactions, addition reactions, elimination reactions, oxidation-reduction reactions, and rearrangement reactions. Each type of reaction involves specific changes in the structure and bonding of organic compounds.
3. What is the difference between alkanes and alkenes?
Ans. Alkanes and alkenes are both types of hydrocarbons, but they differ in their structure and properties. Alkanes are saturated hydrocarbons that contain only single bonds between carbon atoms, while alkenes are unsaturated hydrocarbons that contain at least one carbon-carbon double bond. This double bond gives alkenes different reactivity compared to alkanes.
4. How do functional groups affect the properties of organic compounds?
Ans. Functional groups are specific groups of atoms within an organic compound that determine its chemical reactivity and physical properties. Different functional groups can confer different properties to organic compounds, such as acidity, basicity, polarity, solubility, and reactivity towards specific reactions. Understanding functional groups is crucial in predicting the behavior of organic compounds.
5. What are the major classes of organic compounds?
Ans. Organic compounds can be classified into several major classes based on their functional groups. Some common classes include alkanes, alkenes, alkynes, alcohols, ethers, aldehydes, ketones, carboxylic acids, esters, amines, amides, and halogenated compounds. Each class of compounds has its own unique set of properties and reactions.
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