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.