SB Tutorials

  Inductive Effect The polarization of a σ bond due to electron withdrawing or electron donating effect of adjacent groups or atoms is referred to as inductive effect .  A sigma bond between two atoms, which differ in their electronegativity, is polarized due to displacement of bond pair towards the more electronegative atom. In this process, the electronegative atom gets partial negative charge while the other atom gets partial positive charge. Thus induced polarity is transmitted through the sigma bonds in the molecule by creating a permanent dipole. This phenomenon is referred to as inductive effect. It is represented by an arrow pointing towards the more electronegative atom carrying partial negative charge. Salient features of inductive effect   * It arises due to electronegativity difference between two atoms forming a sigma bond.  * It is transmitted through the sigma bonds . No pi bonds are in...

  Resonance Effect or Mesomeric Effect The electron withdrawing or releasing effect attributed to a substituent through delocalization of p or π electrons, which can be visualized by drawing various canonical forms, is known as mesomeric effect or resonance effect . It is symbolized by M or R. Negative resonance or mesomeric effect (-M or -R): It is shown by substituents or groups that withdraw electrons by delocalization mechanism from rest of the molecule and are denoted by -M or -R. The electron density on rest of the molecular entity is decreased due to this effect. E.g. -NO 2 , Carbony group (C=O), -C≡N, -COOH, -SO 3 H etc. Positive resonance or mesomeric effect (+M or +R):   The groups show  positive mesomeric effect when they release electrons to the rest of the molecule by delocalization. These groups are denoted by +M or +R. Due to this effect, the electron density on rest of the molecular entity is increased. ...

Hyperconjugation (or) No Bond Resonace (or) Baker-Nathan Effect The delocalization of σ-electrons or lone pair of electrons into adjacent  π -orbital or p-orbital is called hyperconjugation.  It occurs due to overlapping of σ-bonding orbital or the orbital containing a lone pair with adjacent π-orbital or p-orbital.  It is also known as “no bond resonance” or “Baker-Nathan effect”. Conditions for hyperconjugation   * There must be an α-CH group or a lone pair on atom adjacent to sp 2 hybrid carbon or other atoms like nitrogen, oxygen etc.  E.g., Alkenes, alkyl carbocations, alkyl free radicals, nitro compounds with α- hydrogen Illustration of Hyperconjugation The displacement of  σ -electrons towards the multiple bond occurs when there are hydrogens on the α-carbon (which is adjacent to the multiple bond). This results in the polarization of the multiple bond.  E.g. In propene, the σ -electrons of C-H...