Abstract：Galaxies in compact groups live in an environment where galaxy interactions play an important role, similar to the situation in the early universe. They are therefore ideal objects to study the influence of the environment on galaxy properties and evolution. The atomic hydrogen is extremely affected by this environment, with high deficiencies in many cases, whereas the molecular gas content is relatively normal in most galaxies. However, the properties of the molecular gas are drastically different if one selects those galaxies, based on their mid-infrared colours from the Spitzer and WISE satallites, that are in transitioning phase from active to quiescent. These so-called “canyon” or "infrared transition zone" galaxies have a considerably lower molecular-to-stellar mass and star formation efficiency than actively star-forming galaxies in compact groups. This shows the transition from active to quiescent is driven both by a loss of molecular gas and the fact that the remaining gas has lost its capacity to form stars efficiently. A likely reason for this result is that gas-gas collisions are taking place in the “canyon” galaxies that produce shocks and inject turbulent energy into the ISM. These processes have been observed and studied in detail in several individual objects, as e.g. in the intergalactic medium of the compact group Stephan’s Quintet or in the collisional bridge of the Taffy galaxies.