DFT (B3LYP, M06-2X) and MP2 methods are applied to the design of a wide series of the potentially 10-C-5 neutral compounds based on 6-azabicyclotetradecanes: XC1(YCH2CH2CH2)3N 1–3, XC1(YC6H4CH2)3N 4–6, XC1[Y(tBuC6H3)CH2]3N 7–9 and carbatranophanes
10–25 (X=Me, F, Cl; Y=O, NH, CH2, SiH2; Z=O, CH2, (CH2)2, (CH2)3). Carbatranophanes 10–25 are characterized by a sterical compression of their axial 3c–4e XC1←N fragment with respect to that in the parent molecules 4–6. A magnitude of the revealed effect depends on a valence surrounding of the central carbon atom C1, the size and the nature of the side chains (Z) that link the “π-electron cap” with a tetradecane backbone. This circumstance allowed us to obtain 10-C-5 structures with the configuration of the bonds around the C1 atom, which corresponds to practically an ideal trigonal bipyramid. In these compounds, the values of the covalence ratio χ of approximately 0.6 for the coordination C1←N contacts with a covalent contribution (atoms in molecules (AIM) and natural bond orbital (NBO)) are record in magnitude. These values lie close to a low limit of the interval of the χSi←D change (0.6–0.9) being characteristic of the dative and ionic-covalent (by nature) Si←D bond (D=N, O) in the known 10-Si-5 silicon compounds.