Advices For Studying Organic Chemistry

4) The energy barriers are still too small to permit isolation of the gauche and

anti conformations at normal temperatures.

Figure 4.8 Energy changes that arise from rotation about the C2–C3 bond of
butane.

3. van der Waals forces can be attractive or repulsive:
   
   
   1. Attraction or repulsion depends of the distance that separates the two groups.
   
   
   2. Momentarily unsymmetrical distribution of electrons in one group induces an
      opposite polarity in the other ⇒ when the opposite charges are in closet
      proximimity lead to attraction between them.
   
   
   3. The attraction increases to a maximum as the internuclear distance of the two
      groups decreases ⇒ The internuclear distance is equal to the sum of van der
      Waals radii of the two groups.
   
   
   4. The van der Waals radius is a measure of its size.
   
   
   5. If the groups are brought still closer —— closer than the sum of van der Waals
      radii —— the interaction between them becomes repulsive ⇒ Their electron
      clouds begin to penetrate each other, and strong electron-electron
      interactions begin to occur.