Gallium nitride (GaN) thin films are grown by metalorganic vapor phase epitaxy (MOVPE). Trimethylgallium (TMG) and ammonia are used as group III and V precursors, respectively. It has been suggested by several past studies that the trimer (or ring compound), [(CH3)(2)GaNH2](3), is formed in appreciable amounts in the gas phase during the MOVPE of GaN and is ultimately responsible for the growth process. However, recent mass spectrometric studies seem to indicate otherwise. The purpose of this paper is to explore this debatable issue using density functional (DFT) and reaction rate theories. The potential energy surfaces, obtained via DFT calculations, are used for calculation of rate constant as a function of pressure and temperature using quantum Rice-Ramsperger-Kassel theory. These rate constants are then used for calculations of concentrations of various species over a range of the III/V ratio at various temperatures. Our results suggest that the ring compound is negligible and cannot initiate the main pathway for growth of GaN.