In this work we evaluated the level of difficulty found in learning stereochemistry concepts, by students intending to teach physical sciences at the Ecole Normale Superieure (ENS) Kouba (Algeria). A paper and pencil questionnaire was administered to 170 students to evaluate: their familiarity with Newman representations; their ability of linking two representation modes (Cram and Newman) of two molecular structures; the students' capacity to identify from different structural representations (Newman and Cram) their stereo-isomerism relationships, and their competence in the use of rules to pass from one mode representation to another (Newman, Cram, Fischer). It was found that many students, despite an effort to use stereochemistry concepts in their approach (configuration, conformation, diasteriomer, enantiomer, observer position), encounter many difficulties in understanding these concepts. We conclude that the origin of these difficulties arises from a lack of integration of definitions and rules, a lack of mastery of techniques to place the observer, poor spatial awareness of structure, and a lack of rigor in the application of different representation conventions. (Contains 2 tables and 15 figures.)