Understanding Medicinal Plants: Their Chemistry and Therapeutic Action
Prof. Bryan Hanson
Instructor's Resource Page for Chapter 2
Many students, particularly science-avoiders, see chemistry as intimidating, and much of that intimidation comes from the diagrams that chemists use – our structures – because they don’t really understand them. The primary goal of this chapter is to reduce any anxiety students have about chemistry and help them become comfortable working with chemical structures - to remind them that they can do this material. I try to help students see that chemical structures are highly symbolic and information-rich, but like any language, chemistry structures are built up from simpler notions. By knowing a few simple rules of bonding, students can decode the many ways that chemists have of drawing structures, and extract the information from within that structure. It’s not nearly as hard as many of them perceive it to be. Basically, we want to build not only Stuctural Literacy but also comfort.Learning Objectives
After completing this chapter, students should:
- Know the valences and common bonding situations of carbon, nitrogen, oxygen and hydrogen.
- Be comfortable in interpreting and using the different styles of drawing structures that chemists commonly use: expanded style, bond-line style, and condensed formulas.
- Know the significance of wedged bonds and dashed bonds in chemical structures, and recognize lone pairs (the origin of lone pairs is discussed in Chapter 3).
- Be able to recognize the common functional groups in both simple and more complex structures, whether they are fully drawn out or in condensed format.
- Have a sense of the different types of chemical names encountered in chemistry and what purposes they serve.
- Know what a molecular formula is, and what information it can and cannot tell you about the structure of a molecule.
- Understand the concepts of isomers (structural or constitutional) and connectivity, and be able to draw several isomers that fit a given molecular formula.
One resource that is very useful for students is a molecular modeling program, such as Spartan or CAChe. Such a program can help students begin to see structures as three-dimensional objects, a skill they will need later, and helps them map the two-dimensional structures onto the computer screen. It also provides them with practice in verifying the bonding in a molecule, as well as recognizing the functional groups. At this early stage, I give students pre-drawn structures of varying complexity, ask them to list the functional groups present and give the molecular formula. This requires that they rotate the molecule on the screen to view it from different angles and in effect, mentally trace the bonding in the entire molecule to answer the questions. Some suggested structures can be downloaded from the course web site in PDB format. It is good to include some smaller structures as well, and to have students make models of these using model kits. By using two-dimensional drawings, three-dimensional structures on the computer screen, and physical models, one can access different learning styles and reinforce concepts. I continually emphasize that two-dimensional structures on paper are highly symbolic in that they are an abstract representation of a molecular reality. In the same manner, it is helpful for students to think of physical models as molecular art, a sculpture so to speak, but an art that represents something very real.
- Chart showing structure skills students should develop.
- Worksheet on expanded structures, bond-line structures, molecular formulas and drawing isomers.
- Chart of functional groups (from UMP)
- Worksheet on identifying functional groups.
- Worksheet on working with condensed formulas.
- Table summarizing typical bonding patterns (from UMP).
- Worksheet with assorted structure styles and tasks (review)
The background on this page is a 19th century woodcut of Phytolacca americana.
Last updated Thursday, September 1, 2011 . Contents & layout copyright 2011 Prof. Bryan Hanson