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Home , Stereochemistry

A CONCEPTUAL UNDERSTANDING OF HIGHER EDUCATION STUDENTS ON STEREOCHEMISTRY

Daniele Raupp1, José Cláudio Del Pino1 and Agostinho Serrano2 1Federal University of Rio Grande do Sul, Post Graduate Program in Science Education, Brazil. 2Lutheran University of Brazil, Canoas, Brazil.

Abstract: The problems related to the formation of scientific concepts of stereochemistry have been widely discussed in the literature. Some researchers made an argument that the main difficulty in solving those problems resides in the three- dimensional level of visualization. Others, however, argue that the learning problem is related to the fact that the topics in organic are introduced in a very arid way to students who cannot relate this ‘school science’ with their previous daily experiences. To analyse the conceptual understanding of higher education students on stereochemistry a group of six students received a blank sheet with an open question. After the student answered this question, we conducted interviews under the Think Aloud protocol. By analysing both the written material and the transcripts of the interviews, we noticed that none of the students mentioned any historical fact connected to the theme or to any experiences of their daily lives. There is an appreciation of aspects such as structure, geometry, molecular formula, and nomenclature. This reflects the thinking of Lima et al (2000) who claim "Teaching chemistry often has summarized the mathematical calculations and memorization of formulas and nomenclature of compounds". This understanding of stereochemistry based only on scientific concepts, can be one of the causes of learning difficulties often reported as commented previously corroborated by the aforementioned statement and Gabel (1993) which attributes the difficulties that beginners have to develop a conceptual understanding: Students cannot understand, "phenomena” that are not considered related to the student's everyday life. Keywords: stereochemistry, classroom observation, conceptual understanding, think aloud protocol.

BACKGROUND AND FRAMEWORK Concepts of isomerism, molecular geometry, three dimensional structures, asymmetric carbon, , and are addressed not only in disciplines of in high school, but as well in higher education. Moreover, in higher education the field of stereochemistry is not only a subject of study in chemistry courses, but also courses in , Pharmacy, and others. The problems related to the formation of scientific concepts in stereochemistry have been widely discussed in the literature, and a consensus has been reached that the main difficulty in solving problems relies in three-dimensional level of visualization required to reason about the phenomena in the molecular level. Difficulty occurs since the ability to visualize three-dimensional aspects of and their relations with other molecules is a considerable challenge (Wu & Shah, 2004; Kozma, Chin, Russel & Marx, 2000). The complexity of problem solving at this level (Baker, George & Harding, 1998) justifies the fact that, for some students, learning stereochemistry can be difficult and sometimes traumatic (Kurbanoglu, Taskesenligil & Sozbilir, 2006). As a result, the weeks spent studying stereochemistry are somehow viewed as frustrating for students (Evans, 1963). Teaching stereochemistry is also a challenge for teachers, as well as to those trying to develop strategies that would facilitate the understanding of scientific concepts, as one must address the overall lack of motivation to study Chemistry itself. The complexity of the issue becomes even more evident when we study the early history of stereochemistry.

The challenge of teaching stereochemistry The concept of chemical space (one of the original names of stereochemistry) for some was considered a reverie, being violently criticized. Now, it is deservedly considered a key concept, without which modern chemistry would be almost inconceivable (Ramberg, 2003). The study of the shape has been of such importance to science that it granted the in 1975 to the two who developed research in the area. The prize was divided equally between John Warcup Cornforth Croatian "for his work on the stereochemistry of enzyme- catalyzed reactions" and "for his research into the stereochemistry of organic molecules and reactions " (Nobel Prize, 2009). But, in the classroom, theses aspects not always are discussed, as Correia et al. (2008) commented, explaining the specific case of Organic Chemistry, the authors claim that it "is introduced so barren for students who cannot relate this school knowledge with previous experience" (2009, p.489). Naturally, seldom the teacher can use as a starting point the so called “everyday knowledge”. It would be startling to relate concepts like conformation, steric hindrance, plane of symmetry and chirality to the spontaneous knowledge of students. In this sense, the lack of student motivation seems to be related to the difficulty in dealing with abstract concepts and not related to their daily lives (Gabel, 1993). According to Lima and colleagues (2000) that "non-contextualization" may be the cause of the high level of rejection of Chemistry that naturally makes the process of teaching and learning somewhat more difficult. The concepts involved in learning stereochemistry are scientific concepts and in order to achieve a cognitive learning of this type of concept cognitive theories demand an action mediated through planned educational activities (Vygotsky, 1993). Santos and Mortimer (1999) discusses that teaching should be contextualized according to the social context considering the economic, social and cultural aspects of the classroom. But differences in approaches aside, it is important to clarify that even employing a contextualized approach to teaching chemistry, there are no guaranties that the classic problems of chemistry teaching will be solved (Chassot, 1993). In other words, relating scientific concepts to everyday phenomena of stereochemistry or even with historicity, does not guarantee success in solving problems teaching in the three-dimensional level. This relationship has the sole purpose of motivating students, since the knowledge that students bring to the classroom come mainly from his interpretation of the macroscopic world. Also, contextualization may help to break some paradigms associated with the level of rejection of learning Chemistry. It is necessary to demystify the image of chemistry as a dogma to avoid the idea of a science basically done by geniuses or something too farfetched (Loguercio et al., 2002).

RESEARCH QUESTION So, with the objective of elucidating more the problem of understanding stereochemistry comprehension by students, the research question that guided the data collection was: What is the conceptual understanding of stereochemistry of undergraduating students in Brazil?

METHODOLOGICAL FRAMEWORK The methodology used in this work consisted of using two different instruments of data collecting: a) The Blank sheet protocol: sheets were distributed, as well as pencils and pens with different colors among the students. They were asked to write and use any sort of drawing to explain their own concept of and b) Think Aloud protocol: interviews focusing on the process used to complete the aforementioned task. Six students participated in the experiment, all of them under graduating in Chemistry, and all of them also who had attended the subjects related to that content at least once previously. The task asked in both instruments was: “Imagine that you are going to explain to another colleague what you know about isomerism. Feel free to write text, equations, formulas, drawings, tables, any way you want.” Upon completion of the tests, we conducted interviews based on technical Think Aloud (Cotton & Gresty, 2006). All interviews were videotaped for later analysis of verbal speech and gestures made during the reporting task execution in the role of representing the different .

RESULTS AND DISCUSSION The theme stereochemistry is not a new theme for the students analyzed. In the third year of school the subject is approached, and we took care to choose a sample that had already taken the course Organic Chemistry also in their undergraduation. By analyzing both the written material as the transcripts of the interviews, we noted that none of the students mentioned any historical fact connected to the theme or any such related to their daily lives. There is an appreciation of aspects such as structure, geometry, molecular formula, nomenclature. This reflects the thinking of Lima et al. (2000) who claim that "Teaching chemistry often has summarized the mathematical calculations and memorization of formulas and nomenclature of compounds, without valuing the conceptual aspects." This understanding of stereochemistry based only on pure scientific concepts, can be one of the causes of learning difficulties often reported as commented previously corroborated by the statement and Gabel (1993) which attributes the difficulties that beginners have to develop a conceptual understanding: Students cannot understand, "phenomena” that were not considered related to the student's everyday life. During the interview, as asked how he designed the structure of the but-2-ene, whose molecular formula is C4H8, Student 1 focuses on explaining how to identify the phenomenon checking whether the two compounds have the same molecular formula. Student 1 remarked: “First we have to see if they are isomers, same molecular formulae, then you have to count element by element to see here, for example, look there is four carbons, six, seven, eight hydrogen and this one here also the cis and the trans.” On the other hand Student 2 focuses on two possible connections of carbon, and even the geometry of the orbital configuration to start the identification of the isomers. He described how he usually analyzes a : “It is like we always do in class, we always, the Teacher he always tells about the three bonding that there are between, existing in the carbon. From those three bonding we start to build the molecules, you know, I tried to explain those three bonding there would explain how it is each one of them. That linear is what makes two double bonding then it is in the plane, it has room for two more ligands, the triple has room for three more and the trigonal, that is a little more complex, it has two orbitals in the plane, one back and one forward.” Student 3 also analyzes the possibilities of connection of said carbon and use the name of the compound as starting point for designing the pairing structure. He said: I always start from the beginning, so to speak. The carbon is tetravalent, with four bonds. The oxygen is bivalent, hydrogen and halogens monovalent and nitrogen is trivalent. This is the essential, the basic that we have to start with. We got to know how many bondings the compound will make. And then, you got to put all this in building the structure. Here it was given the name of the compound then, from the name of the compound we know that there should be four carbons, for example, we can know the function, if it is an alcohol, an acid, ether, etc. Then we keep throwing, connecting carbon with carbon, we place a main chain and then we go placing the other elements till we complete the number of carbons in the molecular structure. And then there are compounds with the same molecular formulae, they have four carbons and six hydrogen, but what differs is how the chain is distributed. Student 2 after commenting how to build their isomers, explained how to identify them: Then besides this the formation of the cis and trans that always catches me, right… and of isomers that we learned till now that I know is that when two elements have the same shape, when they have the same shape and structure they are isomers.”

Then the student ranked isomers correctly, but does not remember the characteristics of each: This is the basic principle and then from that we categorized in three isomers in isolated diasteroisomers, and constitutional isomers. Then to get to these three I cannot explain...”

Student 1 explained stereoisomers using the term “optical isomer” and explains naming rules:

“Here's the starting iodine, bromine, chlorine and hydrogen. Hence in order of priority is putting an exchange hydrogen R is clockwise and counterclockwise is S. In case this would be the part of optical isomerism. Then I put that usually a compound having optical isomerism and has the chiral carbon. Generally, it is not always, and not a rule that carbon is composed of four different ligands to be considered chiral carbon. That part we are seeing in the organic class.

There is no clarity when the conceptual description of the division of isomerism, and also uses the Student 2 explain the term "optical isomer".

I wrote about what I remembered, I do not know precisely… Isomerism is the part of chemistry that studied compounds of the same molecular formula but different functions. There are several types of isomerism among them , isomerism and optical isomerism function . And I do not remember the other kinds that we had in the flowchart of organic types as follows to distinguish what type of isomerism that was. But I remembered basically what we said in both Organic I.

It is important to mention that the term “optical isomerism” is considered by IUPAC an obsolete term and that the textbooks used in higher education, do not use this classification for isomers any longer.

Considering the exposed above, it is possible to conclude that, even with all the freedom to explain the nature of Stereoisomerism, no students in our sample even mention applications, history, or the relevance of stereochemistry. That corroborates with the literature on the subject. We believe that an approach to scientific concepts related to everyday life can arouse students' interest by showing facts; a historical approach can provide an understanding of the dynamic nature of the development of stereochemistry, as well as scientific concepts in general, as being the result of a human construction, derived of a long work of many scientists. Worth to mention that the study of the historical process of the development of science shows the student that even well- known scientists encountered difficulties and questions, so that the student realizes that there was a building path to arrive at the current state of scientific knowledge (Loguercio et al., 2002; Loguercio & Del Pino, 2006).

FINAL CONSIDERATIONS Those are the preliminaries findings of this study: students focused on procedures and how to use mnemonic instruments to conceive isomers and draw them, without ever giving importance to historical aspects or day life connections. This research will further question the reason behind this neglect of historical or day-life knowledge when teaching chemistry by further analyzing textbooks. We aim at proposing a teaching unit for Stereochemistry; this time employing historical and daily concepts allied with the three-dimensional level of visualization to understand the whole phenomena of stereochemistry.

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