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Context. The availability of asteroseismic constraints for a large sample ofred giant stars from the CoRoT and Kepler missions paves the way for variousstatistical studies of the seismic properties of stellar populations.  Aims. We use the first detailed spectroscopic study of 19 CoRoT red-giantstars (Morel et al 2014) to compare theoretical stellar evolution models toobservations of the open cluster NGC 6633 and field stars.  Methods. In order to explore the effects of rotation-induced mixing andthermohaline instability, we compare surface abundances of carbon isotopicratio and lithium with stellar evolution predictions. These chemicals aresensitive to extra-mixing on the red-giant branch.  Results. We estimate mass, radius, and distance for each star using theseismic constraints. We note that the Hipparcos and seismic distances aredifferent. However, the uncertainties are such that this may not besignificant. Although the seismic distances for the cluster members are selfconsistent they are somewhat larger than the Hipparcos distance. This is anissue that should be considered elsewhere. Models including thermohalineinstability and rotation-induced mixing, together with the seismicallydetermined masses can explain the chemical properties of red-giants targets.However, with this sample of stars we cannot perform stringent tests of thecurrent stellar models. Tighter constraints on the physics of the models wouldrequire the measurement of the core and surface rotation rates, and of theperiod spacing of gravity-dominated mixed modes. A larger number of stars withlonger times series, as provided by Kepler or expected with Plato, would helpfor ensemble asteroseismology.

Models of red giants in the CoRoT asteroseismology fields combining asteroseismic and spectroscopic constraints