  BONNFIRES, a new generation of population synthesis code, can calculate
nuclear reaction, various mixing processes and binary interaction in a timely
fashion. We use this new population synthesis code to study the interplay
between binary mass transfer and rotation. We aim to compare theoretical models
with observations, in particular the surface nitrogen abundance and rotational
velocity. Preliminary results show binary interactions may explain the
formation of nitrogen-rich slow rotators and nitrogen-poor fast rotators, but
more work needs to be done to estimate whether the observed frequencies of
those stars can be matched.
