Structurally Sound

I am teaching “Introduction to Organic Chemistry” this semester. I have always struggled with how to present molecular structures to the class as the semester progresses. Molecular structures are so fundamental to organic chemistry, but we make things difficult for ourselves by using a wide variety of different molecular representational styles that follow different rules. I can imagine how confusing this is for a beginning student. I looked through the new “Fundamentals of Organic Chemistry” by McMurry and paid close attention to how molecules were represented. My observations: 1) unshared valence electrons are hidden very early on. Interestingly, they reappear on molecules when mechanisms are introduced. My favorite illustration of this is found in Chapter 3.

2) The bond line form is introduced in the first chapter and frequently used in the first few chapters. The bond line form is very useful for someone who is well acquainted with molecule formulas, however, it is not especially appropriate for a student who is being introduced to organic chemistry. I agree that it is important for a student to be able to interpret structures they find in Wikipedia, chemical catalogs, and databases. But this does not mean that we should use the bond line form as a teaching tool. 3) To make matters more confusing, Lewis, condensed, and bond-line forms and are mixed together. Maybe we should have a new rule: “If you cannot be accurate, at least be consistent.” 4) In my mind, the tradition text-friendly condensed form should be banned. Stringing together atoms with no suggestion of where bonds would go is like writing an ancient language that was written without punctuation to separate words, phrases, and sentences! (CH3)2CH(CH­2)2C(CH3)3

One more example from Chapter 3:

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2 Comments

  1. Posted January 16, 2010 at 9:38 pm | Permalink

    “If you cannot be accurate, at least be consistent.”

    How about if I am consistently inaccurate? =)

    It took me forever to figure out why H+ went to the right carbon and not the left–and then I realized that you can rotate the molecule! And I love how the lanosterol shows bond angles and the ethyl chloride/chloroethane doesn’t. Now I learned that C2H4 + HCl –> CH3CH2Cl. =)

    • Posted January 26, 2010 at 12:26 pm | Permalink

      The missing lone pair on an atom performing a nucleophilic attack is one of my top pet peeves in organic textbooks.


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