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New proton sponges with cyclopropeniminophospazenes as pincer ligands have been designed. It was shown that cyclopropeniminophosphazenes possess a gas phase basicity higher than the corresponding phosphazenes. Due to their lower steric demand in comparison to phosphazenes, cyclopropeniminophoshpazenes can be utilized in the design of synthetically accessible proton sponges with exceptionally high gas phase and solution phase basicity, with calculated PA values up to 330 kcal mol −1 and p K a in acetonitrile of 48.5 units.

Utilizing dialkylamino cyclopropenimines as hydrogen bond acceptors in tri-substituted guanidines and cyclopropenimines, we computationally designed the most basic superbases possessing intramolecular hydrogen bonds (IHB-superbases) so far. The values of proton affinity in the gas phase range between 296.6 and 306 kcal mol−1, with estimated pKa values in acetonitrile between 35.5 and 39.7. The obtained PAs of five new IHB-superbases surpass the basicity of the paradigmatic P4-tBu Schwesinger phosphazene, whereas pKa values come close to that of P4-tBu. None of the designed superbases contain phosphorus, which puts them among few most basic non-phosphorus superbases desiged so far.

It is shown by a reliable DFT method that supramolecular structures 1 and 2, constructed using pyridine as an essential building block, act as powerful neutral organic superbases in the gas phase and in acetonitrile due to cationic resonance and hydrogen bonding in the conjugate acids amplified by the NMe2 groups placed at strategic positions on the molecular backbone.

The absolute proton affinities (APA) of 20 α-amino acids, as obtained by the MP2(fc)/6-311+G∗∗//HF/6-31G∗ + ZPVE(HF/6-31G∗) and the scaled Hartree–Fock (HFsc) models, are presented. It is shown that the α-NH2 group is protonated in all but four cases: lysine (K), proline (P), histidine (H), and arginine (R). There is a good overall agreement with experimental data measured by the kinetic method. However, there are some notable exceptions such as glutamine (Q) and lysine (K), where strong hydrogen bonds in the protonated forms occur. It is suggested that the present results and theoretical models employed could be useful for resolving such experimental ambiguities. Furthermore, it appears that the HFsc model provides an efficient tool for elucidating APAs of artificial α-AAs, derivatives of natural α-AAs and their oligomers.

The spatial and electronic structure of the parent 2-tetrazene and its tetramethyl- and ethyl derivatives are examined by an ab initio approach. It is shown by using the MP2(fc)/6-311+G ∗∗ //HF/6-31G ∗ + ZPVE (HF/6-32G ∗ ) model that alkylated tetrazenes exhibit strong intrinsic basicity as evidenced by their high absolute proton affinities. The latter is due to the appreciable electron density concentration at the terminal nitrogen atoms, the increased II-electron delocalization in conjugate acids and the electron density relaxation effect occurring upon protonation.

The absolute proton affinity of a group of compounds involving AN imino group is examined by employing the MP2(fc)/6-311+G ∗∗ // HF/6-31G ∗ + ZPVE(HF/6-31G ∗ ) theoretical model. It appears that these systems exhibit high proton affinity thus representing good candidates for efficient proton sponges. Their heavily substituted derivatives, involving bulky alkyl groups, which protect the reactive double bonds, should possess even higher proton affinity being at the same time apt to chemical synthesis.