Multiple stellar populations (MPs) are widely identified in Galactic globular clusters (GCs), which are characterized by variations in light element abundances. Such variations have not been found in open clusters (OCs). Mass has been considered as a key parameter for constraining MPs models, and a mass threshold that separates GCs from OCs may exist. Research of MPs can provide a threshold for OCs and GCs.We looked for MPs signals in Whiting 1, traditionally known as a young, low-mass GC associated with the Sagittarius dwarf spheroidal galaxy.We obtained low-resolution spectra with $\lambda\lambda=3850-5500 \AA $ for 8 giant members of Whiting 1 using the Magellan telescope. We measured spectral indices related to CN and CH molecule features and derived C and N abundances. The variations of C and N abundances are comparable to their measurement errors ($\sim0.1$ dex), therefore we do not detect any MPs signal in Whiting 1. The absence of MPs in this cluster is probably due to its low-compactness and high-metallicity environment found in younger Sagittarius star clusters. Given the similar age, metallicity, horizontal branch morphology, and absence of MPs in younger Sagittarius star clusters, we suggest that Whiting1, Terzan7, and Palomar 12 are open clusters, like Berkeley29. We suggest that there is a possible border between OCs and GCs in the metallicity vs. compactness index parameter space.