Coupling between iso(thio)cyanates and amines, alcohols, and thiols to yield (thio)urea/urethane in the gas phase is important for the vacuum deposition processes of functional organic thin films such as molecular layer deposition or chemical vapor deposition. In this study, the kinetics and thermodynamics of 12 reactions between bifunctional reactants containing ANCO/ANCS and ANH 2 /AOH/ASH moieties were calculated using double-hybrid density functional theory to find systematic structure-reactivity relationships. The activation energy for the proton-transfer step was correlated with the basicity of the nucleophile/Brønsted acid reactants, while the exothermicity of the coupling reaction depends on whether the other functionality is ANCO or ANCS.Analysis of the transition states revealed that the location of the transition state is affected by the basicity of the reactants. Vibrational and electronic spectra of the product were obtained to help future experimental investigations. K E Y W O R D S density functional theory, isocyanate, isothiocyanate, oligomerization, polymerization | I N T R O D U C T I O NVapor-phase polymerization techniques for the deposition of organic thin films, such as chemical vapor deposition (CVD) and molecular layer deposition (MLD), is gaining large research interests. The advantages of gas-phase deposition of polymeric thin films include precise control over thickness, conformality of coating over high-aspect-ratio structures, facile inclusion of functional moieties, and large scalability. [1,2] CVD and MLD processes have successfully yielded thin films of target polymers for various potential applications, including formation of films with lateral patterns [3] and vertically alternating laminates [4] at nanoscale, use as a metal diffusion barrier [5] and optical filters, [6] and func-Int J Quantum Chem 2017;117:e25341.