Organic chemistry is the chemistry of carbon compounds.

Carbon atom have a tendency to form bonds between its own atoms to form long chains. This property is called catenation.

Curved arrow indicates the movement of electrons, not the movement of atoms.

Full arrowhead indicates the movement of two electrons simultaneously and half -headed arrow represent the movement of single electron

Homolytic fission and heterolytic fission.

When a covalent bond breaks in a symmetrical manner such that each fragment retains an unpaired electron, the process is called homolytic fission or homolysis

When a covalent bond breaks in an unsymmetrical manner such that one of the fragments retains both the bonding electrons, the process is called heterolytic bond fission or heterolysis.

Electrophiles, Nucleophiles and free radicals

Electrophiles- They are electron deficient and can accept an electron pair in a reaction. They are lewis acids which are positively charged or neutral species.

H+, Cl+, Br+,NO₂+,BF₃,AlCl₃ etc

They are electron rich having lone pair of electrons. They are lewis bases which may be negatively charged ions or neutral molecules having lone pairs.

OH- , H₂N- ,R-, NH₃, H₂O

They are neutral species with unpaired electrons. Highly reactive and is formed by homolytic fission.

Cl. , CH₃. , C₆H₅

• effect of displacement of bonding electrons. • Electron displacement effect may be permanent or temporary.

1. Inductive effect 2. Electromeric effect 3. Mesomeric effect 4. Hyperconjugation 5. Steric effect

• The polarization of a sigma bond due to electron withdrawing or electron donating effect of adjacent groups or atoms is called inductive effect or l effect. • It is a permanent electron displacement effect.

+I EFFECT- The polarization of sigma bond due to the presence of electron donating groups.

I EFFECT- The polarization of sigma bond due to the presence of electron withdrawing groups.

(CH₃)₃C > (CH₃)₂CH > CH₃CH₂ > CH₃

NO2 > CN > COOH > F > Cl > Br > I > OCH3

Chloroacetic acid is stronger than acetic acid

Because in chloroacetic acid -I effect of Cl group decreases electron density around carboxyl hydrogen. Also because of the dispersal of negative charge on the carboxylate ion, the ion is stabilized than acid. In acetic acid due to the +I effect of CH3 group acidity decreases.

Since there are three Cl groups in trichloroacetic acid, -I effect would be more than in dichloroacetic acid. So acid strength of trichloroacetic acid is greater.

The acid dissociation constant (Ka) of a solution is pKa. The pKa value is one method of determining an acid's strength. A lower pKa value denotes a more powerful acid. For example, a lower number indicates that the acid dissociates more entirely in water. As acid value increases Pka value decreases

H-COOH > CH₃-COOH > CH₃-CH₂-COOH Propanoic acid is least acidic due to the +I effect of CH2-CH3 group. Acetic acid is comparatively stronger and the strongest acid is formic acid

F-CH₂COOH >Cl- CH₂COOH > Br- CH₂COOH > I-CH₂COOH This is because the electronegativity order of halogens are F > Cl > Br > I

This is because the intensity of inductive effect decreases with increasing distance of electron withdrawing substituents.

Temporary effect involving the complete transfer of a shared pair of pi- electrons of a multiple bond to one of the bonded atoms, in the presence of an attacking reagent

Electromeric effect

+E effect, the Electromeric shift of pi- electrons of a multiple bond is towards that atom to which reagent gets attached.

-E effect, the Electromeric shift of pi- electrons of a multiple bond is away from that atom to which the reagent gets attached.

Acetaldehyde and CN-

explaination

The polarity induced in a molecule by the interaction of two pi- bonds or between a pi- bond and lone pair of electrons present

GroupsWhen present adjacent to conjugated multiple bonds ,bring resonance by withdrawing pi-electrons of multiple bond thereby causing electron displacement towards themselves . The effect produced is called -R/-M effect. eg crotonaldehyde vinyl cyanide

C=O, NO2, COOH

with one or more lone pairs whenpresent adjacent to multiple bond, bring resonance by releasing electrons in the direction of multiple bond thereby causing electron displacement away from themselves. The effect produced is called +R/+M effect. eg vinyl chloride methyl vinyl ether

Comparison of electron density of benzene, nitrobenzene and aniline

The pi electrons of benzene ring are uniformly delocalized. They are easily attacked by electrophiles. However, substituted benzene show +M or -M effect. The substituents can either donate or withdraw electron density from ring.

NO2 is a group which shows – M effect. They make the benzene ring less reactive towards electrophilic substitution reactions by withdrawing electrons from the ring by resonance. Such groups are called deactivating groups or substituents.

NH2 is a group which shows +M effect. They make the benzene ring more reactive towards electrophilic substitution reactions by donating electrons to the ring by resonance. Such groups are called activating groups or substituents.

Delocalization of electrons by the overlap of a sigma bond orbital with a pi- or p-orbital is called hyperconjugation.

Hyperconjugation

In propene,CH3 group is attached to C=C that has a pi- bond. The sigma orbital of C-H bonds of CH3 is in conjugation with pi orbital of double bond

Hyperconjugation is also called no-bond resonance since there is no real bond between Carbon and Hydrogen in hyperconjugative structures. But the H+ ion is bound firmly to pi bond and is not free to move.

In But-1-ene, there are two hydrogen atoms attached to alpha carbon atom. Hence, two hyperconjugative interactions are possible. In But-2-ene, there are 6 hydrogens attached to alpha carbon atom and 6 hyperconjugative interactions are possible. As the number of hyperconjugative structures are greater for But-2-ene, it is more stable

in explanation

Steric effect refers to the spatial interaction which arises due to the spatial crowding of bulky groups in a molecule.

They affect the stability of the molecule as the groups do not get enough space for their accommodation and also there occurs repulsion between them. • They also obstruct the approach of attacking reagents.

In cis-2-butene, the two bulky methyl groups are on the same side of double bond. They are close to each other and cause spatial crowding. In trans-2-butene,the two groups are on the opposite side of double bond and there is no crowding. So, cis-2-butene is less stable.

Anti- staggered conformation of butane is more stable since the two methyl groups are far away from each other. In fully eclipsed conformation, the two methyl groups are near to each other. Hence it is least stable.

In terms of Inductive effect, we would expect trimethylamine is more basic than dimethylamine or methylamine because an increase in number of methyl groups increase the electron availability at Nitrogen atom. However, the order of basicity of the above amines in aqueous solution is as follows The lower basicity of trimethylamine is due to steric effect of the three methyl groups which hinders the approach of the proton and also hinders the stabilization of resulting trimethylammonium ion through solvation.

Acidity of carboxylic acid is decreased by the presence of bulky groups as they cause steric hindrance to the solvation of carboxylate ion through solvation.

The decrease in rate of esterification is due to steric effect on acids which hinders the approach of alcohol to reaction site on acids.

in explanation

This is because the two methyl groups sterically hinder the approach of alcohol.

The intermediate species formed during the stepwise progress of a reaction to reach its preferred products are called reaction intermediates.

They are short-lived, high energy and highly reactive molecules. • They may be cations, anions or neutral species with one or more unpaired electrons.

carbocations, carbanions, free radicals etc

• Carbon bearing a positive charge is called carbocation. • Carbocation has only six valence electrons. • Electron deficient species.

pic

Formed by heterolytic cleavage of covalent bonds.

in explanation

 Cabon atom in a cabocation is sp² hybridized.  The three sp² hybrid orbitals form σ-bonds with three groups or atoms.  One vacant p-orbital remain unhybridised and lies perpendicular to the plane.  Carbocation has trigonal planar shape with bond angle 120°.