The knowledge about the intrinsic thermochemical properties such as heat of formation (ΔHf), gas-phase basicity (GB), and proton affinity (PA) is one of the keys points to understand the molecular reactivity. Protonated species are central to many chemical processes, such as acid-base phenomena, chemical ionization mass spectrometry, electrospray ionization mass spectrometry, surface chemistry and many other aspects of biophysics such as protein conformation. The ability to calculate thermochemistry properties by using theoretical methods would be advantageous, particularly when experimental measures are difficult to perform. The development of composite ab initio methods has made a great advancement in computational thermochemistry, but a high precision is difficult to obtain even using these methods. In the present study, the heat of formation of 2-pirrolidinone and γ-butirolactone was calculated by three isodesmic reactions, using the chemical models G3, G2, G2(MP2), CBS-Q, CBS-4, CBS-QB3, and DFT methods (B3LYP, B3P86, mPW1PW, PW91PW91, PBE1PBE, and B98) with the 6-31G(d), 6-31+G(d), 6-31G(d,p), 6-31+G(d,p), 6-31++G(d), and cc-pVDZ basis sets. Our results indicate that DFT methods present the most accurate heat of formation for γ-butirolactone. On the other hand, for 2-pyrrolydinone, G2 and G2(MP2) present the best agreement with experimental heat of formation. The proton affinity and basicity of the γ-butirolactone were obtained and compared with the experimental values, described in the literature (PA = 200.8 kcal.mol^-1 and GB = 193.1 kcal.mol^-1). The smallest errors were obtained by using the models B3LYP/6-31+G(d,p), B3LYP/6-31++G(d,p), G2, G2(MP2) and CBS-Q.

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1. Effect of Substituents and Protonation on the Electronic Structure of [2.2]Paracyclophane