In the Classroom
Octachem Model: Organic Chemistry Nomenclature Companion Joaquin Palacios Departmento de Fisicoquímica, Facultad de Química, UNAM, Ciudad Universitaria, México D.F. 04510, México;
[email protected] During the Middle Ages chemicals were named according to their origin, properties, or application. When the number of organic compounds grew large, the need for systematic nomenclature was evident. Efforts by researchers produced advances; in the resulting system of nomenclature structure is the basis for identifying, classifying, and naming chemicals (1, 2). In the 1930s, a committee for the revision of organic chemistry nomenclature was created by the International Chemical Union. In a meeting in London 1947, it became evident that the nomenclature had to be modified and extended. As a result of several international conferences and meetings, today we have a consistent nomenclature system based on general concepts that are applied to journals, patents, textbooks, and so forth (3–7). The IUPAC nomenclature rules are a central topic in chemistry courses. Chemical nomenclature is critical to the science of matter transformation since the study of chemical reactions and their mechanisms is recognized as difficult without a good knowledge of the chemical structures. Furthermore extensive use of systematic and trivial names in organic chemistry courses complicates nomenclature. The correct application of nomenclature rules facilitates global communication since the structures can be considered the language of chemistry. In my teaching experience with chemical engineering students, I observed that they have difficulties identifying organic chemistry functional groups. As a consequence it was a challenge to communicate the correct names of organic substances that the students study in their courses. As an example, in a polymer class, most of the students were unable to identify the difference between a polyether and a polyester and, most of the time, they could not associate the polymer’s configuration with the monomers from which the macromolecules originated. As a possible solution to this problem I designed the Octachem model (8).
Figure 1. Octachem model designed to help students practice using rules of organic chemistry nomenclature. This is a simplified image of the actual Octachem model.
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The Octachem model is a three-dimensional interactive toy used to prompt high school and college students to apply organic chemistry nomenclature rules. Through several cooperative group activities, the students learn and practice the concepts of functional group, compound families, and structure–properties relations. The Octachem model is an amusing didactic tool, a physical model each student can use in class and at home. Students can practice the chemical nomenclature rules so they can recognize the configurations of many simple organic compounds. Theoretical Background Octachem’s design was based on several concepts of the structure of organic compounds: • The molecules of organic compounds are integrated by atoms or groups of atoms recognized as monovalent or polyvalent species. • The atoms or groups of atoms in a molecule can be interchanged between molecular structures; this can be accomplished in a transformation process, called a chemical reaction. • Groups of atoms with a configuration and defined intrinsic chemical properties are recognized as functional groups and are classified in families. A list of functional groups used in Octachem are presented in Tables 1 and 2. • Playing with Octachem, the principal chemical functional groups and their names can be easily remembered and used to draw or sketch the structure of organic chemicals.
Description of Octachem Model The Octachem model was built on the modularity of organic functional groups as dictated by valence. The Octachem model is a rod with three independently moving modules shaped as octagons (Figure 1).1 The two end octagons have monovalent species pictured on the rectangular faces, R1 and R2, while the center octagon shows the most common functional groups studied in basic organic chemistry courses (carbonyl, carboxyl, oxygen atom, etc.), labeled the G species. By rotating the three octagons, different molecules can be generated whose identities can be assigned a three digit code (a, b, c) for easy identification during the teaching and learning processes. Each rectangular face is marked with a number from 1 to 8, in addition to the name of a particular radical and its formula. The chemical structures are formed by two monovalent species plus one G species. The complete structure of one organic molecule is identified by the Octachem three digit
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In the Classroom
code, (a, b, c), and the IUPAC nomenclature system is then used to give the correct name. Since the modules can rotate independently a large number of compounds can be displayed. Practicing Organic Chemistry Nomenclature with Octachem Several activities can be implemented in the classroom or during individual study with the Octachem model. Naming the generated chemical structures is the most direct and popular possibility. Another activity is assigning the correct IUPAC name to a compound designated by the three digit code (a, b, c). According to our experience, aiding students in their study of the organic chemistry nomenclature will lead to a better understanding of the intrinsic chemical properties associated with certain functionalities and the identification of a family of compounds. The interactive contact with Octachem only requires simple instructions: first, rotate the left, middle, or right octagonal module of Octachem; next align the edges of the three modules; identify the G species shown on the central module by comparing its structure with the configurations of the G species shown in Tables 1 and 2. Then identify and give the IUPAC or the trivial name of the structure of the monova-
lent species on the lateral or external modules. Finally, after the complete molecular structure is recognized, give the correct name for the chemical compound, following the IUPAC nomenclature system. Several activities have been designed to encourage students to work hard with the Octachem model in the organic chemistry nomenclature topics. In one of these activities, we asked the students to classify chemical structures by families or form a family of compounds. As an example we asked the students to give the chemical structures and names of a family of unsaturated hydrocarbons, alkenes. Some of the members of this family were identified as vinyl compounds, which are monomers that can be polymerized (9, 10). In this activity the functional G species was identified, ⫺HC⫽CH⫺, next the lateral monoradicals were accommodated in sequential order, increasing the numbers of the digits code. The ⫺CH⫽CH⫺ and ⫺C⬅C⫺ species can form alkenes and alkynes with one or two substituents in their molecules. The ⫺NH⫺ species can form primary or secondary amines. As mentioned before, it is possible to integrate chemical structures if we choose a group G from the list shown on the central module of Octachem and a hydrogen atom from the right module. Then if we rotate the left module from a low number to a higher one, chemical structures of a family of molecules are formed.
Table 1. Functional Groups –G– Shown on the Central Module of Octachem Family
⫺G⫺ Group
Nomenclature
Linear hydrocarbons
⫺CH2⫺
Prefix + -ane; CH3⫺(CH2)3⫺CH3 pentane
Aldehyde
>C⫽O
R⫺CH⫽O; prefix + -anala; CH3⫺CHO ethanal
Ketone
RR´C⫽O; prefix + -anoneb; (CH3)2⫺C⫽O; 2-propanone (acetone or dimethyl ketone)
Alcohol
>C⫽O ⫺O⫺
Ether
⫺O⫺
R⫺O⫺R´; denote alcohol component with -yl suffix; CH3⫺O⫺CH3 dimethyl ether
Acid
⫺COO⫺
R⫺COOH; prefix + -oic acid; CH3⫺COOH ethanoic acid
Ester
⫺COO⫺
R⫺COO⫺R´; denote alcohol component with -yl suffix; acid with -oate or -ate suffix; CH3⫺COO⫺CH3 methyl acetate
Alkenes, vinyl
⫺CH⫽CH⫺
R⫺CH⫽CH⫺R´; add -ene to prefix; use number to denote C⫽C position; CH3⫺CH⫽CH2 1-propene
Benzene/arene
⫺C6H4⫺
R⫺C6H4⫺R´; denote substituent using group name and ring position; radical name + benzene; Cl⫺C6H4⫺Cl 1,4-dichlorobenzene
R⫺OH; prefix + -anol; CH3⫺OH methanol (methyl alcohol)
Alkynes
⫺C⬅C⫺
R⫺C⬅C⫺R´; add –yne to prefix; number to denote position of triple bond; HC⬅CH ethyne
Amine
⫺NH⫺
R⫺NH⫺R´; denote alcohol component with -yl suffix; CH3⫺NH⫺CH2⫺CH3, ethyl methyl amine
a This works, if there are only single bonded carbons on the rest of the molecule. Double bonds on the carbon chain, prefix+enal, triple bond on the chain, prefix+ ynals. bSame as (a) with anones, enones, ynones
Table 2. Monovalent Groups R1 and R2, Groups –G– as Shown on the Octachem Model Module 1
Module 2 ⫺G⫺ Group
R1– Monovalent Group
Module 3 –R2 Monovalent Group
1 H⫺ hydrogen
1 ⫺CH2⫺ methylene
1 ⫺H hydrogen
2 CH3⫺ methyl
2 >C⫽O aldehyde or ketone
2 ⫺CH3 methyl
3 CH3CH2⫺ ethyl
3 ⫺O⫺ alcohol or ether
3 ⫺CH2CH3 ethyl
4 C6H5⫺ phenyl
4 ⫺COO⫺ acid or ester
4 ⫺C6H5 phenyl 5 ⫺Cl chloro
5 ClCH2⫺ α-chloro
5 ⫺CH⫽CH⫺ alkene
6 HO⫺ hydroxy
6 ⫺C6H4⫺ benzene/arene
6 ⫺OH hydroxy
7 CH3(CH3)CH⫺ isopropyl
7 ⫺C⬅C⫺ alkyne
7 ⫺CH(CH3)CH3 isopropyl
8 CH2⫽CHCH2⫺ allyl
8 ⫺NH⫺ amine
8 ⫺CH⫽CH2 vinyl
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In the Classroom
As another activity, we suggest organizing a contest among the students. For a short period of time, such as 15 minutes, the students identify and name as many chemical structures as they can. The student who gives the correct names for the highest number of chemical compounds is recognized. In this activity, the students write the molecular structures and the IUPAC names of all substances formed in their notebooks. Another way of playing with Octachem consists in asking the students to give the chemical structure and name of the compound whose Octachem three digit code is given, for example, the chemical structure and name of the (1, 1, 1) compound. These coordinates correspond to the first element of the homologous hydrocarbons series, methane H– CH2–H (see Table 2). Finally two additional examples of nomenclature problems are presented. To form a family of alcohols, we choose the biradical ⫺O⫺, number 3, from the central module of Octachem. Next rotate the right module to the position marked with the number 1, ⫺H, then rotate the left module, starting at the position number 2, CH3⫺, in this manner, the structure of methanol CH3⫺O⫺H is identified. Rotating the left module to the next position, marked with the number 3 and so forth, the configurations of ethanol, phenol and α-chloromethanol can be obtained. To integrate the formula of an ester derived from formic acid, HCOOH, first we choose the divalent ester group from the central module, ⫺COO⫺, rectangular section number 4, next rotating the right module, starting from position 1, ⫺H, we can identify the structure of the formic acid (1, 4, 1), from there, we move to the next position (1, 4, 2), this corresponds to the chemical structure of methyl formate. The next position (1, 4, 3) corresponds to ethyl formate, and the position (1, 4, 4) gives us, the structure of phenyl formate. In this manner we can integrate a family of esters derived from organic acids plus alcohols. Discussion The Octachem model has been presented to several groups of first-year undergraduate students in organic chemistry in a two-hour class. First the fundamental concepts involved in the design of the model were discussed, then we explained the usage and the information available in the octagonal solid model. During the next 40 minutes the students worked with Octachem, wrote the chemical structures, the names of molecules, and the Octachem coordinates of the compound in their notebooks. At the end of session, the didactic possibilities of the model were discussed among the students. The class enjoyed the experience of playing with Octachem. After a two-hour session the students wanted to keep on practicing with the model and it was necessary to stop the activity. High school and first-year students got enthusiastic after playing with Octachem. In one week they were
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able to recognize the structures and gave the correct names of hydrocarbons, alcohols, aldehydes, amines, acids, esters, ethers, and dienes. In class, cooperative groups were organized. These groups played with Octachem, recognized, and gave the correct names of a large number of chemical compounds. The results of the experience were very promising since students reported, “playing with Octachem was a very stimulating activity” and “Octachem model is very ingenious and amusing, it helps a lot in the process of learning different chemical structures and their names”. Another student reported his experience in this way: “playing with Octachem is an interesting way to look over organic chemistry. I would like more functional groups to be included in the model. I think it would be possible to have an specific model for the commercial monomers”. Finally a college chemistry student stated, “if I had worked with Octachem in high school, Organic Chemistry 1, would had been very easy for me”. Note 1. The Octachem model has three octagonal solid modules. A metallic rod joins the three modules, and each module can move independently. The eight faces of the central and lateral modules are rectangles of 2.5 × 6.0 cm.
Literature Cited 1. Chang, R. Química, 2nd ed.; McGraw Hill: México City, 1997. 2. Cram, D.; Hammond, G. S. Organic Chemistry; McGraw Hill: New York, 1980. 3. Fletcher, J. H.; Derme, O. C.; Fox, R. B. Nomenclature of Organic Compounds, Principles and Practice; Advances in Chemistry Series, 126; American Chemical Society: Washington DC, 1974. 4. IUPAC. Nomenclature in Organic Chemistry, 3rd ed.; Butterworths: London, 1971. 5. International Union of Pure and Applied Chemistry Organic Division; Commission on Nomenclature of Organic Chemistry. Pure Appl. Chem. 1983, 55, 409. 6. McMurry, J. Química Orgánica, 5th ed.; International Thompson Editors: México City, 2001. 7. Morrison, R. T.; Boyd, R. N. Organic Chemistry; Allyn & Bacon Inc.: Boston, 1998. 8. Palacios, J. OCTACHEM 3D, Modelo Didáctico para la Enseñanza de la Nomenclatura en Química Orgánica. Comunicación para Derechos de Autor, Instituto Mexicano de Protección Industrial, México D.F., 2003. 9. Stevens, M. P. Polymer Chemistry an Introduction; AddisonWesley Co.: London, 1995. 10. Wingrove, A. S.; Caret, R. L. Química Orgánica; Harla: México City, 1984.
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