Notes – Advanced Organic Chemistry

CHAPTER 2

* A conjugated molecule has single and double bonds occurring alternatively as in the following: -C=C-C=C-C=C-C=C- while a molecule have isolated double bonds does not have this feature, such as in -C=C-C=C-C=C-C=C-. A typical example of distinguishing the two types is shown in the structures of isomeric pentadienes:

  H2C=CH-CH=CHCH3 H2C=CH-CH2-CH=CH2
  1,3-pentadiene 1,4-pentadiene
  a conjugated diene containing a non conjugated diene containing
  conjugated double bonds isolated double bonds

In conjugated molecules resonance structures are considered which impart stabilization as compared to others in which isolated double bonds are present.

** Also called delocalization energy. You have already learnt about the delocalization of electrons while studying the orbital representation of benzene.

* This can be extended to γ hydrogen atoms in some cases.