This study sought investigate: i) the understanding of isomerism by future chemistry teachers during initial training; and ii) the construction of isomer concepts after an approach centered on problem situations (SP's). Two problem situations related to isomerism (historical context and medicinal applications) were elaborated. A textual learning material developed for this purpose and concrete molecular models were used of system resources in the problem situation resolution process. Data were

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... olleted using a questionnaire, field observation and semi-structured interview, and analyzed according to the ideas presented by Meirieu (1998). The two SP's had obstacles, transposable to only a few of the nine groups that responded. Inadequate use of the isomer concept was observed in many of the responses considered scarcely satisfactory or unsatisfactory.