  We compute the coefficients of the effective mass operator of the 1/Nc
expansion for negative parity L=1 excited baryons using the Isgur-Karl model in
order to compare the general approach, where the coefficients are obtained by
fitting to data, with a specific constituent quark model calculation. We
discuss the physics behind the fitted coefficients for the scalar part of the
most general two-body quark-quark interaction. We find that both pion exchange
and gluon exchange lead to the dominance of the same operator at the level of
the effective mass operator, which is also observed from data.
