ORGANIC CHEMISTRY- I (NATURE OF BONDING AND STEREOCHEMISTRY)- TAUTOMERISM

ORGANIC CHEMISTRY- I (NATURE OF BONDING AND STEREOCHEMISTRY)- TAUTOMERISM

**Tautomers are isomers of a compound, which differ only in the position of the protons and electrons. The carbon skeleton of the compound is unchanged but functional groups are different's. 

**The alpha - hydrogen of carbony1 compounds is acidic, as it is connected with the alpha - carbon that is directly bound to the electron withdrawing carbony1 group. This is the main reason for the tautomerism to occur. 

**The acidifies of these alpha-hydrogen atoms is enhanced if an electron withdrawing group is attached to the alpha -carbon atom. 

**The establishment of equilibrium may be catalyzed by both acids and bases. Through suitable means, such as by fractional crystallization or careful distillation in the absence of any acid and any base, the keto and the enolic form may be separated from each other.

** It is generally difficult to say which is the labile form, since very often a slight change in the conditions, e.g., temperature, solvent, shifts the equilibrium from keto to enol or vice versa. 

**Many scientists have suggested various forms and theories of tautomerism and this module discusses an exhaustive list of some different types of tautomerism.

  ORGANIC CHEMISTRY- I (NATURE OF BONDING AND STEREOCHEMISTRY)- TAUTOMERISM

ORGANIC CHEMISTRY- I (NATURE OF BONDING AND STEREOCHEMISTRY)- APPLICATIONS OF ELECTRONIC EFFECTS

ORGANIC CHEMISTRY- I (NATURE OF BONDING AND STEREOCHEMISTRY)- APPLICATIONS OF ELECTRONIC EFFECTS

**Greater is the delocalization of the charge, greater is the stability. Electron donating groups (+I, +M and +H) hence, stabilize electron deficient species like carbocation and free-radicals. On the other hand, Electron withdrawing groups (-I and -M) hence, stabilize electron rich species i.e, carbanions. 

**In a molecule having an electronegative atom joined directly to H atom, the acidity is affected by Ease of Deprotonation and Stability of conjugate base. 

**Both these conditions are enhanced by introducing electron withdrawing groups (-M, -H or -I )and decreased by electron donating groups (+I, +M, +H). Remember that the second condition is more dominant one than the first to arrive to the conclusion. Hence if two are opposing, rely on the second one. 

**Hence, electron donating groups (+I, +M, +H) increase the basicity; and electron withdrawing groups (-I, -M) decrease the basicity. 

**An electron releasing substituent like -CH³ increases the basicity of aniline and an electron-withdrawing substituent like-X or -NO² decreases the basicity. 

**Ortho/meta/para directive influence in electrophilic substitution of substituted benzene is affected by the electronic effects of the substituent. 

**All ortho/para directing groups are activating except halogens. On the other hand, all electron withdrawing groups are deactivating.

  ORGANIC CHEMISTRY- I (NATURE OF BONDING AND STEREOCHEMISTRY)- APPLICATIONS OF ELECTRONIC EFFECTS

ORGANIC CHEMISTRY- I (NATURE OF BONDING AND STEREOCHEMISTRY)- HYPER-CONJUGATION

ORGANIC CHEMISTRY- I (NATURE OF BONDING AND STEREOCHEMISTRY)- HYPER-CONJUGATION

**The delocalization of sigma electrons or lone pair of electrons into adjacent π-orbital or p-orbital is called hyper conjugation. 

**It takes place because of overlapping of sigma-bonding orbital or the orbital containing a lone pair with an adjacent untitled p-orbital. It is also called as "no bond resonance" or "Baker-Nathan effect" 

**It explains stability of alkenes, carbocations and free radicals. 

**The dipole moment of the molecules and bond length is greatly affected due to hyperconjugation since the contributing structures show considerable polarity and change in bond order. 

**Hyper conjugation also explains the reactivity & orientation of electrophilic substitution on alky1 substituted benzene ring. 

**The overall tendency of anomeric substituents to favour an axial position is called Anomeric effect. For example. the alpha-methy1 glucoside is more stable than the Beta

**For alpha-halo alkenes, the delocalization of electrons takes place towards the halogen group through hyperconjugative mechanism because of electron withdrawing nature of halogen. It is known as reverse hyperconjugation.

  ORGANIC CHEMISTRY- I (NATURE OF BONDING AND STEREOCHEMISTRY)- HYPER-CONJUGATION

ORGANIC CHEMISTRY- I (NATURE OF BONDING AND STEREOCHEMISTRY)- RESONANCE, CONJUGATION AND CROSS CONJUGATION

ORGANIC CHEMISTRY- I (NATURE OF BONDING AND STEREOCHEMISTRY) - RESONANCE, CONJUGATION AND CROSS CONJUGATION

Resonance is very common and significant feature of many organic molecules. Due to its presence, there is a pronounced influence on the structure, chemical reactions and physical properties of such molecules. 

**Resonance energy is defined as the energy difference between the most stable resonating structure and the resonance hybrid structure.

** Resonance increases stability by increasing the bonding between adjacent atoms and by distributing charge over a greater number of atoms. 

**A cross-conjugated system has a double-bonded unit single-bonded to one of the middle atoms of another conjugated chain. On the other hand, a normal conjugated system such as a polyene typically has alternating single and double bonds along consecutive atoms.

**Conjugation is broken completely by the introduction of saturated (sp3) carbon:

 

ORGANIC CHEMISTRY- I (NATURE OF BONDING AND STEREOCHEMISTRY)- REVISIT TO ELECTRONIC EFFECTS: INDUCTIVE AND MESOMERIC EFFECTS

ORGANIC CHEMISTRY- I (NATURE OF BONDING AND STEREOCHEMISTRY)- REVISIT TO ELECTRONIC EFFECTS: INDUCTIVE AND MESOMERIC EFFECTS

The atoms/groups which are more charge on them and withdraw the electrons of the carbon chain towards themselves are known to exert-I Effect (pronounced as "minus I effect") electronegative than carbon gain a slight negative The atoms/groups which are more electropositive than carbon gain a slight positive charge on them and push the electrons of the carbon chain away from themselves are known to exert +I Effect (pronounced as "plus I effect") The atoms/groups in which lone pair(or electrons of negative charge) is in conjugation with double or triple bond are electron donating and gain a formal positive charge in the resonating structure in the process and are known to exert +M/+R Efect. The atoms/groups which are in conjugation with double or triple bond and are electron withdrawing and gain a formal negative charge in the resonating structure in the process and are known to exert -M/-R Effect.