No, it is not possible. Roles can be assigned in a particular context only and groups are not a context. Enrolled users have particular role in the context of the course and can have eventually different role in the context of individual activity modules in the course. So your student "S" could have a role "Student" in the course "C" and role "Teacher" in some particular activity - such as Assignment or Forum within the course. But group membership does not affect roles.
Maybe you can try and describe what you want to achieve from a pedagogical / teaching / learning perspective, there might be some alternative solutions.
