Chemical Intuition

While organic chemistry is arguably one of the toughest courses it is also one of the coolest and most interesting subjects you will ever take.  In this course, you will learn to how to manipulate atoms and molecules on the quantum scale.  You will learn to make molecules (pharmaceuticals, pesticides, dyes, etc.)  and materials (plastics and other polymers).  No other course, except in maybe some art classes, will you learn to make things.

I hope you will also learn to see these molecules and materials differently as you develop your chemical intuition.  When an organic chemist looks at a molecule he sees it differently than other scientists and some chemists would.  As you begin to explore the fascinating world of organic chemistry always keep in mind that molecular structure controls the physical and chemical properties of a given molecule.  When you look at a molecule ask yourself these questions and in time you will develop your chemical intuition.

• What structural features are present and how do they relate to the physical properties (i.e. boiling point, melting point, solubility, and chromatography)?
• What are the important intermolecular (secondary) forces resulting from these structural features?
  
  
• What structural features are present and how do they relate to the chemical reactivity?
• Where are all the electrons?  Are they in lone pairs, π bonds, or HOMO? 
• Where aren't the electrons?  Are there empty orbitals or a LUMO?
• Are there acidic protons or basic lone-pair electrons?
  
  

Let's briefly look at one of the first structures we will explore, ethene, a member of the alkene family.  The four structures/models below show the different levels of detail for ethene.  On the left is the simplest approximation.  Notice how a π bond is no different from a σ bond in the simple line bond structure.  You should remember from general chemistry that π bonds are different from a σ bond and this structure doesn't provide that detail.  The two structures on the right are the Quantum Mechanically (QM) derived HOMO and electrostatic potential maps.  When an organic chemist sees the structure on the left they envision the two structures on the right.  From these structures, we can easily understand why alkenes behave like nucleophiles in additional reactions.  A nucleophile likes to react with something positive.

Line Bond representation	Line bond (showing HOMO)	QM derived HOMO	QM derived electrostatic potential