What’s in an organic compound name?

At the University of Toronto, introductory organic chemistry is taught to life science undergraduates through two single-semester courses: one in their first year of studies, and the other in second year.¹ For a number of years I have instructed the initial four weeks of the first-year course when offered during the fall semester. I routinely start discussing fundamental principles of structure and bonding, and move on to atomic hybridization models and resonance concepts. Then, after beginning to talk about the idea of functional groups, and molecules known as alkanes, we reach the point where naming organic compounds is on the agenda.

In-class polls and informal discussions during office hours, as well as conversations with high school teachers have revealed that many students are well-versed in the basics of organic nomenclature (and often much more than the basics). They are knowledgeable of the IUPAC rules,² which may or may not have been their only previous exposure to organic chemistry. Being conversant with the rules of naming can be linked to Canadian high school science curricula. For example, the Ontario Grade 12 science curriculum (section B2.2, Organic Chemistry)³ states the following:

“(By the end of this course, students will) use International Union of Pure and Applied Chemistry (IUPAC) nomenclature conventions to identify names, write chemical formulae, and create structural formulae for the different classes of organic compounds, including hydrocarbons, alcohols, aldehydes, ketones, carboxylic acids, esters, ethers, amines, amides, and simple aromatic compounds”.

The word “identify” in this statement — and its position in the statement — seems to underscore the significance of students knowing and being able to apply IUPAC nomenclature rules. However, is it more important to memorize these rules, or to read names of organic molecules (e.g., 2-butene, but-2-ene) and be able to draw structures from them? In reality, it is the latter that is much more critical for practicing scientists. Our students will undoubtedly encounter many compound names in textbooks and the primary research literature — some of which are correct according to IUPAC, and some which are not. Many chemists are unaware of the current rules, and simply use the name that seems most appropriate — and hopefully unambiguous! — to them. Becoming capable of reading a name and converting it to a skeletal structure^{4, 5} that clearly indicates correct atom connectivity and stereochemistry should be a key learning objective. Sometimes a student may say, “I’ll just Google the name of a compound to find the structure,”… but not all known organic molecules have a Wikipedia entry! Chemists may have to take a quite complex name and draw the structure before they can comprehend its physical, chemical and biological properties.

I should clarify that I am not downplaying the usefulness of knowing the rudimentary tenets of organic nomenclature — indeed, a colleague and I co-authored two short articles that attempted to summarize some major principles in 2009.^{6, 7} As chemistry educators though we should grasp the point that IUPAC rules are a human invention, and are subject to change — in fact, they have changed over the years. Do you prefer 2-butene or but-2-ene? To return to our first-year course — I typically spend five minutes outlining the current basics of naming organic compounds, and then focus on getting students to deconstruct the names of some simple/branched alkanes and to draw their skeletal structures. When new functional groups are introduced later on in the course (e.g., alcohols), I talk about “-ol” and “hydroxyl-” as a naming suffix and prefix respectively. Knowing that an enantiomer has a specific configuration at a stereocentre is crucial from recognizing “R” or “S” at the beginning of a name, as well as appreciating the descriptors “E” and “Z” for stereoisomeric alkenes. Moving into second-year, understanding how other functional groups are incorporated into a name is covered, (e.g., “amino” as a prefix and “amine” as a suffix for –NH₂). Importantly, students are never asked to derive IUPAC names of compounds in term tests or final examinations — they are expected to draw molecules based on names provided to them.

As high school teachers and university instructors, we are, at least to some extent, fighting against the perception that organic chemistry is a memorization discipline. I would argue that teaching students to memorize multiple nomenclature rules early on in their exposure to the discipline serves to reinforce that notion. Students can in fact learn the simple, introductory rules of naming themselves, and appreciate that drawing molecules from names is much more relevant. Perhaps the Ontario Grade 12 science curriculum might better read: “(by the end of this course, students will) use International Union of Pure and Applied Chemistry (IUPAC) nomenclature conventions to RECOGNIZE names”... ?

Acknowledgement

I would like to thank Dr. Kristine Quinlan for some very helpful comments regarding this article.

Literature cited

1. K.B. Quinlan and A.P. Dicks, Beyond the “Lecture” Theatre: First-Year Chemistry Learning Resources, Chem 13 News 2015, 414, 14-15.
2. H.A. Favre and W.H. Powell, Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names 2013. Royal Society of Chemistry, Cambridge, U.K., 2013.
3. Ontario Grade 11 and 12 Science Curriculum 2008, page 108, www.edu.gov.on.ca/eng/curriculum/ secondary/2009science11_12.pdf (accessed January 2017).
4. S. Skonieczny, and A.P. Dicks, Representing Organic Molecules with Skeletal Formulae, Chem 13 News 2011, 381, pages 6-7.
5. Skeletal Formulae Revisited, S. Skonieczny and A.P. Dicks, Chem 13 News 2013, 399, page 8.
6. S. Skonieczny, and A.P. Dicks, Nomenclature of Organic Compounds – Part I, Chem 13 News 2009, 368, pages 9-11.
7. S. Skonieczny, and A.P. Dicks, Nomenclature of Organic Compounds – Part II, Chem 13 News, 2009, 369, pages 13-15.   

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