Thermochemical Insights on Small Nitrogen Heterocyclic Compounds

Abstract Along this overview, a comprehensive thermochemical discussion of small nitrogen heterocyclic molecules is presented, based on reliable information obtained by experimental and computational methodologies. Calorimetric data jointly with other data obtained from alternative sources are used to acquire extensive thermochemical information. A brief description is provided on the more common techniques used in the measurement of properties of compounds under analysis, as well as fundaments on methodologies used in computational approaches, to establish alternative strategies to derive data for other species. Data analysis is fundamentally focused on the standard molar enthalpy of formation, an essential thermodynamic parameter to assess the energy associated to chemical reactions or other transformations involving the compounds, also allowing to derive related thermodynamic properties. This study focuses on neutral, π conjugated, nitrogen heterocyclic five‐membered systems with 1–4 heteroatoms, and some substituted derivatives, complemented by a short discussion on other species having one benzenic ring fused to the heterocycle. Considering its role on chemical structure and reactivity properties, the establishment of intermolecular hydrogen bonding deserved special attention. Complementarily, NH bond dissociation enthalpy values along different aza systems are analyzed and used on comparing thermodynamic favorability of corresponding bond disruptions. An enthalpic parameters database for the selected groups of compounds is reportedly commented, gauging about their reliability to be assumed as key values.