Design of Jacob’s ladder-based teaching aids for illustrating the dualities of benzene derivatives

3.1 Structure of benzene

Jacob’s ladder 1 showcases a full structural formula of benzene, with all element symbols and bonds on the front side and a line-angle formula of benzene on the back. This helps illustrate the relationship between these two formulas (Figure 2(1) ). While full structural formulas are comprehensive, they are time-consuming to draw. Line-angle formulas simplify this process by eliminating the need to draw carbon and hydrogen elemental symbols. Jacob’s ladder 2 was used to introduce the ball-and-stick and space-filling models (Figure 2(2) ). The former vividly depicts bond lengths and angles, while the latter emphasizes the space occupied by atoms.

3.2 Nomenclature of benzene derivatives

Jacob’s ladder 3 was used to demonstrate the relationships between preferred and systematic IUPAC names (Figure 2(3) ). The surface of this ladder was equipped with hook-and-loop fasteners where students and the instructor could attach letter plates (Figure 3(b)). Three representative examples were introduced: for C₆H₅–CH₃, the preferred and systematic IUPAC names are toluene and methylbenzene, respectively; for C₆H₅–OH, they are phenol and benzenol; and for C₆H₅–NH₂, they are aniline and phenylamine. C₆H₅–, which represents a benzene ring with one hydrogen removed, is referred to as the phenyl group. The preferred IUPAC names for these benzene derivatives are listed in our country’s high school chemistry textbooks. Depending on the student’s abilities, introducing C₆H₅–OCH₃ (anisole or methoxybenzene) or C₆H₅–CH=CH₂ (styrene or ethenylbenzene) may be suitable.

3.3 Ortho-, para-, and meta-directors

The surface of Jacob’s ladder 4 also includes hook-and-loop fasteners for attaching substituent plates. The front side features a painted image of phenol, while the backside displays a nitrobenzene image (Figure 2(4) ). Jacob’s ladder 4 is used to illustrate the differences in further nitration reactions between phenol and nitrobenzene, specifically concerning ortho-, para-, and meta-directors. This exercise takes advantage of the fact that the hook and loop of hook-and-loop fasteners stick together, but the loop with loop or hook with hook do not. On the phenol side, the ortho- and para-positions of the benzene ring feature the hook side of the fasteners, while the meta-positions feature the loop side. Conversely, on the nitrobenzene side, the ortho- and para-positions of the benzene ring feature the loop side, with the meta-positions displaying the hook side. The back surfaces of the NO₂ plates have the loop side of hook-and-loop fasteners. Students can observe the differences in the positioning of the additional nitro group, as shown in Figure 4.

Figure 4:

Nitration reactions of phenol and nitrobenzene.

The instructor provides a brief explanation of electrophilic aromatic directing groups using Jacob’s ladder 5 (Figure 2(5) ). In general, benzene derivatives with electron-donating groups, such as phenol, aniline, and toluene, tend to produce ortho- and para-substituted derivatives. Introducing picric acid (2,4,6-trinitrophenol) helps explain the relationship between electron-donating substituents and ortho-para- direction, a topic covered in standard chemistry textbooks. Conversely, benzene derivatives with electron-withdrawing groups, like nitrobenzene, are more likely to undergo substitution reactions at the meta position. Benzene derivatives with electron-withdrawing groups are less prone to subsequent electrophilic substitution due to the reduced electron density of the benzene ring. The chemical reactions discussed here leverage the fact that substitutes are positively charged and are attracted to electrons, hence the term electrophilic substitution. Therefore, the substituents react with the part of the benzene ring that carries a more negative charge.

4.1 Lecture for AP students

The AP high school students achieved high scores on both quizzes conducted immediately after the lecture and a week later. These positive outcomes can be attributed not only to the efficacy of the Jacob’s ladder-based teaching aids but also to the high intellectual aptitude of the AP students. Topics such as the ortho-, para-, and meta-directors of benzene derivatives are briefly touched upon in some AP chemistry textbooks, but the electron density of aromatic rings is seldom discussed in regular lectures. Extracurricular lectures for AP students typically favor slightly challenging topics not covered in standard lectures. Hence, in this lecture, we introduced the concept of benzene directors.

4.2 Lecture for nonchemistry majors

At the start of the semester, some nonchemistry majors struggled to accurately identify the composition of benzene and its derivatives as presented in the line-angle formula. To address this, we introduced teaching aids like Jacob’s ladder 1. While these students had learned how to draw molecules using the line-angle formula in high school chemistry, many had forgotten this skill. Jacob’s ladder 1 served as a useful tool to help them recall the relationship between full structural and line-angle formulas. Using Jacob’s ladder 3, we explained the relationship between preferred and systematic IUPAC names of simple benzene derivatives. Structural formulas for toluene and aniline are challenging to associate with their preferred names, but it is easier to connect them with their systematic names. Phenol was chosen to illustrate that the C₆H₅‒ group is known as the phenyl group. As anticipated, the concepts of ortho-, para-, and meta-directors of benzene derivatives proved challenging for the students. However, the correct answer rate for the quiz regarding nitration of nitrobenzene, conducted one week after the lecture, increased slightly among civil engineering majors. Their accurate responses to a quiz about the structure of picric acid suggest that the peer support offered by some students after the lecture was successful.

4.3 Impression of the lecture

The teaching aids based on Jacob’s ladder sparked students’ interest. Students who had never seen a Jacob’s ladder before were fascinated by the spinning panels. A post-lecture questionnaire revealed high levels of satisfaction among most participants.

While instructors could simply print the dualities of benzene derivatives on both sides of A4 paper and show it to students, we believe that adding a touch of creativity can make lectures unique and memorable. In this era of computer graphics and 3D-printed teaching aids, there is still a place for handmade aids like those developed in this research. Even though computer graphics and 3D printers are undoubtedly excellent teaching tools, they can be challenging to operate. For students familiar with digital images, tangible learning materials might offer a refreshing change. More recently, reports have highlighted the success of puzzle- and toy-based materials (Silve et al., 2022), further emphasizing their positive reception among students.