Intra-annular cyclophane diamines as proton sponges: a computational study |
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Authors: | Bishwajit Ganguly Debasis Koley |
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Institution: | a Central Salt and Marine Chemicals Research Institute, GB Marg, Bhavnagar 364002, Gujarat, India b Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, D-45470 Mülheim an der Ruhr, Germany |
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Abstract: | Gas-phase proton affinities of cyclophanes containing intra-annular amino groups were calculated using density functional theory (DFT) at the B3LYP/6-31+G∗∗//B3LYP/6-31G∗ level. They are higher in magnitude as those for proton sponges such as 1,8-bisaminonaphthalene, however, they are slightly weaker bases than 1,8-bis(dimethylamino)naphthalene. The high basicity of the cyclophane diamines is attributed mainly to their structural flexibility, which allows them to maximize the hydrogen bond strength in the cations by achieving N-H?N linearity, while strain relief upon protonation is less important. Another contributing factor is the stabilizing interaction of the added proton with adjacent phenyl π systems of the cyclophanes. Barriers for proton transfer between the nitrogen atoms of the diamine cations are also reported. |
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Keywords: | Cyclophane diamines Proton sponge H-bonds DFT calculations |
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