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A CONCEPTUAL UNDERSTANDING OF HIGHER
EDUCATION STUDENTS ON STEREOCHEMISTRY
Daniele Raupp
1, José Cláudio Del Pino
1 and Agostinho Serrano
2
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 chemistry 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, absolute configuration, and chirality are addressed not only in disciplines of
Organic Chemistry 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 Biology, 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 molecules 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
scientists 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 molecule shape has been of such
importance to science that it granted the Nobel Prize in Chemistry in 1975 to the two
chemists 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 Vladimir Prelog "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 Stereoisomerism 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 isomers.
RESULTS AND DISCUSSION
The theme stereochemistry is not a new theme for the students analyzed. In the third
year of secondary 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 isomer:
“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, enantiomers 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.
REFERENCES
Baker, R. W., George, A.V & Harding, M. M. (1998). Models and Molecules—A
Workshop on Stereoisomers. Journal of Chemical Education, 757, 853.
Chassot, A. (1993). Catalisando transformações na Educação. (3 ed.), Editora Unijuí.
Ijuí.
Cotton, D. & Gresty, K. (2006). Reflecting on the think-aloud methods for evaluating e-
learning. British Journal of Educational Technology 37(1), 45-54.
Correia, P. R. M.; Donner Jr., J. W. A. & Infante-Malachias, M. E. (2008). Concept
mapping as a tool to break disciplinary boundaries: isomerism in biological systems.
Ciência & Educação, 14(3),483.
Evans, G. G. (1963). Stereochemistry in the Terminal Course. Journal of Chemical
Education, 40, 438–440.
Gabel, D. (1993). Use of the Particle Nature of Matter in Developing Conceptual
Understanding, Journal of Chemical Education,70(3), 193.
Kozma, R.; Chin, E.; Russell, J. & Marx, N. (2000). The Roles of Representations and
Tools in the Chemistry Laboratory and Their Implications for Chemistry Learning
Journal of the Learning Sciences,9(2), 105.
Kurbanoglu, N. I.; Taskesenligil, Y. & Sozbilir, M. (2006), Programmed instruction
revisited: a study on teaching stereochemistry. Chemistry Education Research and
Practice, 1, 13.
Lima, J.F.L.; Pina, M.S.L.; Barbosa, R.M.N. & Jófili, Z.M.S. (2000). Contextualização
no ensino de cinética química. Química Nova Na Escola, 11, 26.
Loguercio, R. Q.; Souza, D.O & Del Pino, J. C. (2002). A Educação e o Livro didático.
Educação, 48, 183.
Loguercio, R. Q.; Souza, D.O & Del Pino, J. C. (2006). Contribuição da História e da
Filosofia da Ciência para a construção do conhecimento científico em contextos de
formação profissional da química. Acta Scientiae, v. 8(1), 67-77.
Nobel Prize. The Nobel Prize in Chemistry 1975: John Cornforth, Vladimir Prelog.
http://www.nobelprize.org/nobel_prizes/chemistry/laureates/1975.
Ramberg, P.J. (2003). Chemical structure, spatial arrangement: the early history of
stereochemistry, 1874-1914 (pp. 87-109). Aldershot: Ashgate.
Santos, W.L. & Mortimer, E.F(1999). A dimensão social do ensino de Química – Um
estudo exploratório da visão de professores. II Encontro Nacional de pesquisa em
Educação em Ciências.Valinhos.
Vygotsky, L.S. (1993). Pensamento e linguagem. São Paulo: Martins Fontes.
Wu, H.K. & Shah, P. (2004). Exploring visuospatial thinking in chemistry learning.
Science Education, 88, 3, 465.