Synthesis and structural studies of a new class of quaternary ammonium salts, which are derivatives of cage adamanzane type aminal 1, 3, 6, 8-tetraazatricyclo[22.214.171.124,8]undecane (TATU)
© Rivera., et al 2011
Received: 23 August 2011
Accepted: 20 September 2011
Published: 20 September 2011
Novel mono N-alkyl quaternary ammonium salts (3a-f) were prepared using the Menschutkin reaction from the cage adamanzane type aminal 1,3,6,8-tetraazatricyclo[126.96.36.199,8]undecane (TATU) and alkyl iodides, such as methyl, ethyl, propyl, butyl, pentyl and hexyl iodide (2a-f), in dry acetonitrile at room temperature.
The structures of these new quaternary ammonium salts were established using various spectral and electrospray ionization mass spectrometry (ESI-MS) analyses. Compound (3b) was also analyzed using X-ray crystallography.
It was noted that alkyl chain length did not significantly affect the reaction because all employed alkyl iodide electrophiles reacted in a similar fashion with the aminal 1 to produce the corresponding mono N-quaternary ammonium salts, which were characterized by spectroscopic and analytical techniques.
Quaternary ammonium salts have multiple uses in industry, in laboratories and in the household. These compounds act as disinfectants, antiseptic agents, surfactants, fabric softeners, corrosion inhibitors, emulsifiers and antistatic agents (e.g., in shampoos). In organic syntheses, these compounds are used as phase transfer catalysts for a wide range of organic reactions involving immiscible solvent systems . In recent years, interest in ammonium salts has concerned their utilization in templating organic molecules in the synthesis of zeolites, e.g., in photoreactions of chirally modified zeolites , in the synthesis and mechanism of decomposition study of triazenes , in the obtention of ionomers with photoluminescent properties  and for obtaining new Rh and Ag complex , and the use of these ammonium salts as ionic liquids and energetic molecular compounds . These quaternary ammonium salts can react with alkyl halides, leading to the formation of new ammonium salts, which are promising candidates for new zeolite templates and energetic molecular compounds.
Results and Discussion
Reaction of 1 with alkyl iodides 2a-f produced 3a-f in good to excellent yields using the standard protocols for the alkylation of amines. The reaction products were separated by precipitation from dry acetonitrile solution. In the FT-IR spectra of 3a-f (in KBr), alkyl chains showed absorption bands at 2960-2830 cm-1 for asymmetric and symmetric stretching vibrations. Absorption bands at 1148-1136 cm-1, which were related to symmetric C-N stretching vibrations, were observed. The signals at the masses of 169.1449, 183.1587, 197.1730, 211.1923, 225.2120, 239.2291, and 253.2441 in the ESI-MS spectra in the positive ion mode were assigned to the respective charged quaternary ammonium ions of compounds 3a-f. The fragmentation patterns of these spectra were found to be similar to one another.
Crystal data and structure refinement for 1-ethyl-1,3,6,8-tetraaza-tricyclo[188.8.131.52,8]undecan-1-ium iodide 3b
Crystal system, space group
Unit cell dimensions
a = 12.8935 (3) Å
b = 12.8935(3) Å
c = 18.4328 (4) Å
α = 90°
β = 90°
γ = 120°
2653.77 (10) Å3
Z, Calculated density
9, 1.746 g/cm
F (0 0 0)
0.42 × 0.34 × 0.25 mm
θ range for data collection
Max/min. indices h, k, l
-16/16, -16/16, -22/22
9196/2386[R(int) = 0.014]
θMax (°)/Completeness (%)
Full-matrix least-squares on F2
Goodness-of-fit on F2
Final R indices[I > 3σI]
R1 = 0.0106, wR2 = 0.0317
R indices (all data)
R1 = 1.06, wR2 = 3.17
Largest diff. peak and hole
0.19 and -0.13 e Å-3
Fukuy index by 3b
The structure solution was complicated by twinning and by the presence of heavy atoms, namely iodine atoms, which made it difficult to recognize the organic molecule and disentangle the twinning. In the diffraction pattern, every third layer contains strong reflections, while the intervening layers are much weaker. This phenomenon is observed because the iodine atoms occupy positions that make a 9-fold smaller subcell, and the true cell is created only by the organic moieties. The crystal used for the structure solution was an especially well-ordered one in which the superstructure reflections are sharp and can be integrated. The structure has a layered structure along c with layers of organic molecules separated by layers of iodine with hexagonal symmetry. The organic molecules are aligned one on the top of one another, and, between them, there are nearly empty channels that are filled by the ethyl groups of the molecules. It is not surprising that, under non-equilibrium crystallization conditions, the layers tend to stack in a disordered fashion, and, sometimes, the next layer is stacked such that its molecules lie above the channels in the bottom layer. If such a stacking fault occurs frequently, we obtain a completely disordered crystal with, on average, nine times a smaller unit cell. For less frequently occurring stacking faults, the crystal can be better modeled as a twin. This property is observed in the case of the current structure. The twinning law is a mirror plane perpendicular to a (or, equivalently, b).
It was noted that alkyl chain length did not significantly affect the reaction because all employed alkyl iodide electrophiles reacted in a similar fashion with the aminal 1 to produce the corresponding mono N-quaternary ammonium salts, which were characterized by spectroscopic and analytical techniques. Furthermore, 1 only reacts with alkyl iodides, and the quaternization occurs regioselectively on the nitrogen with major sp3 character, which prevents its further alkylation even in a large excess of electrophile. The elucidation of the structure of compound 3b, both in the solid state and in solution, has revealed that nN-σ*CH2-N3R+ orbital overlap confirms that an anomeric effect is present in the ammonium salt. This straightforward, one-step process provides a convenient preparative method for mono-N-alkylated quaternary ammonium salts and could be of interest to investigate the kinetic and thermodynamic properties of the Menschutkin reaction.
General and Instrumentation
NMR spectra were performed in D2O on a Bruker Avance 400 operating at 400.13 MHz (1H), and 100.4 MHz (13C) at room temperature; chemical shifts were referenced to deuterium (1H) and to external CDCl3 (13C). Infrared spectra were recorded as KBr discs on a Perkin-Elmer Paragon FT-IR instrument in the range of 4000-600 cm-1. MS-ESI mass spectra were obtained with a Micromass Technologies-LCT Premier XE Waters; melting points were taken in capillaries on an Electrothermal 9100 melting point apparatus and are presented without correction. Compound 1 was synthesized according to a previously reported procedure . Solvents and reagents were distilled before use. Crystals suitable for single-crystal X-ray determination were produced by keeping a solution of 3b in water for several days at room temperature.
General procedure for the synthesis of compounds 3a-f
To a solution of 1 (0.154 g, 1.0 mmol) in dry acetonitrile (5 mL) was added an equivalent amount (1.0 mmol) of the respective alkyl iodide (2a-f). The reaction mixture was stirred at room temperature for 5 h until a precipitate was observed. The resultant precipitate was filtered under vacuum, washed successively with chloroform and dried in vacuo (Scheme 1).
1-methyl-1,3,6,8-tetraazatricyclo[184.108.40.206,8]undecan-1-ium iodide (3a)
Was isolated as a white solid highly hygroscopic, (0.216 g, 73%). M.p. = 117-118.3°C (decomposition), FT-IR (KBr) vmax: 2994, 2974, 2946, 1473, 1454, 1405, 1387, 1347, 1321, 1296, 1256, 1235, 1158, 1128, 1114, 1044, 1022, 993, 979, 965, 925, 881, 843, 813, 771, 737, 694, 656, 582, 529, 497, 471, 455, 423 cm-1. 1H NMR (400 MHz, D2O) δ (ppm): 2.64 (s, 3H, H-12), 3.42 (s, 4H, H-4 and H-5), 3.97 (d, J = 16.0 Hz, 2H, H-7a and H-10a), 4.52 (d, J = 12.0 Hz, 2H, H-2c and H-11c), 4.56 (d, J = 16.0 Hz, 2H, H-7b and H-10b), 4.81 (s, 2H, H-9), 4.82 (d, J = 12.0 Hz, 2H, H-2d and H-11d). 13C NMR (100 MHz, D2O) δ (ppm): 41.9 (C-12), 55.3 (C-4 and C-5), 69.1 (C-7 and C-10), 79.0 (C-9), 80.5 (C-2 and C-11). MS (ESI+): m/z 169.1449 [C7H14N4+CH3].
1-ethyl-1,3,6,8-tetraazatricyclo[220.127.116.11,8]undecan-1-ium iodide (3b)
Was isolated as a white solid hygroscopic, (0.270 g, 87%), M.p. = 120-121.0°C (decomposition), FT-IR (KBr) vmax: 2959, 2937, 1473, 1454, 1405, 1387, 1347, 1321, 1296, 1256, 1235, 1158, 1128, 1114, 1044, 1022, 993, 979, 965, 925, 881, 843, 813, 771, 737, 694, 656, 582, 529, 497, 471, 455, 423 cm-1. 1H NMR (400 MHz, D2O) δ (ppm): 1.31 (t, J = 8.0 Hz, 3H, H-13), 3.06 (q, J = 8.0 Hz, 2H, H-12), 3.44 (s, 4H, H-4 and H-5), 4.00 (d, J = 12.0 Hz, 2H, H-7a and H-10a), 4.56 (d, J = 12.0 Hz, 2H, H-7b and H-10b), 4.64 (d, J = 12.0 Hz, 2H, H-2c and H-11c), 4.82 (s, 2H, H-9), 4.83 (d, J = 12.0 Hz, 2H, H-2d and H-11d). 13C NMR (100 MHz, D2O) δ (ppm): 5.8 (C-13), 51.8 (C-12), 55.3 (C-4 and C-5), 69.6 (C-7 and C-10), 77.9 (C-9), 78.2 (C-2 and C-11). MS (ESI+): m/z 183.1587 [C7H14N4+C2H5].
1-propyl-1,3,6,8-tetraazatricyclo[18.104.22.168,8]undecan-1-ium iodide (3c)
Was isolated as a white solid hygroscopic, (0.292 g, 90%), M.p. = 123.2-124°C (decomposition), FT-IR (KBr) vmax: 2957, 2935, 1459, 1402, 1389, 1345, 1324, 1260, 1226, 1161, 1112, 1049, 1033, 1009, 969, 948, 877, 814, 746, 655, 449, 423 cm-1. 1H NMR (400 MHz, D2O) δ (ppm): 0.98 (t, J = 4.0 Hz, 3H, H-14), 1.74 (m, J = 4.0 Hz, 2H, H-13), 2.91 (m, J = 4.0 Hz, 2H, H-12), 3.43 (s, 4H, H-4 and H-5), 4.00 (d, J = 16.0 Hz, 2H, H-7a and H-10a), 4.56 (d, J = 16.0 Hz, 2H, H-7b and H-10b), 4.64 (d, J = 12.0 Hz, 2H, H-2c and H-11c), 4.83 (s, 2H, H-9), 4.84 (d, J = 12.0 Hz, 2H, H-2d and H-11d). 13C NMR (100 MHz, D2O) δ (ppm): 10.6 (C-14), 14.0 (C-13), 55.3 (C-4 and C-5), 58.0 (C-12), 69.6 (C-7 and C-10), 78.2 (C-9), 78.7 (C-2 and C-11). MS (ESI+): m/z 197.1730 [C7H14N4+C3H7].
1-butyl-1,3,6,8-tetraazatricyclo[22.214.171.124,8]undecan-1-ium iodide (3d)
Was isolated as a white solid hygroscopic, (0.287 g, 85%), M.p. = 127.2-128.1°C (decomposition), FT-IR (KBr) vmax: 2964, 2931, 2871, 1462, 1403, 1359, 1338, 1312, 1261, 1222, 1160, 1143, 1112, 1049, 1029, 1006, 973, 938, 886, 856, 814, 780, 736, 653, 528, 453 cm-1. 1H NMR (400 MHz, D2O) δ (ppm): 0.93 (t, J = 8.0 Hz, 3H, H-15), 1.34 (m, J = 8.0 Hz, 2H, H-14), 1.67 (m, J = 8.0 Hz, 2H, H-13), 2.92 (m, J = 8.0 Hz, 2H, H-12), 3.40 (s, 4H, H-4 and H-5), 3,96 (d, J = 12.0 Hz, 2H, H-7a and H-10a), 4.52 (d, J = 12.0 Hz, 2H, H-7b and H-10b), 4.61 (d, J = 12.0 Hz, 2H, H-2c and H-11c), 4.83 (s, 2H, H-9), 4.85 (d, J = 12.0 Hz, 2H, H-2d and H-11d). 13C NMR (100 MHz, D2O) δ (ppm): 12.9 (C-15), 19.8 (C-14), 22.1 (C-13), 55.3 (C-4 and C-5), 56.3 (C-12), 69.6 (C-7 and C-10), 78.2 (C-9), 78.6 (C-2 and C-11). MS (ESI+): m/z 211.1923 [C7H14N4+C4H9].
1-pentyl-1,3,6,8-tetraazatricyclo[126.96.36.199,8]undecan-1-ium iodide (3e)
Was isolated as a white solid hygroscopic, (0.306 g, 87%), M.p. = 130.0-131.5°C (decomposition), FT-IR (KBr) vmax: 2953, 2922, 2867, 1464, 1403, 1341, 1313, 1291, 1263, 1238, 1161, 1144, 1099, 1050, 1032, 976, 938, 903, 888, 814, 728, 653, 528, 451 cm-1. 1H NMR (400 MHz, D2O) δ (ppm): 0.89 (t, J = 8.0 Hz, 3H, H-16), 1.33 (m, J = 8.0 Hz, 4H, H-15 and H-14), 1.68 (m, J = 8.0 Hz, 2H, H-13), 2.91 (t, J = 8.0 Hz, 2H, H-12), 3.40 (s, 4H, H-4 and H-5), 3.97 (d, J = 16.0 Hz, 2H, H-7a and H-10a), 4.52 (d, J = 16.0 Hz, 2H, H-7b and H-10b), 4.61 (d, J = 12.0 Hz, 2H, H-2c and H-11c), 4.80 (s, 2H, H-9), 4.81 (d, J = 12.0 Hz, 2H, H-2d and H-11d). 13C NMR (100 MHz, D2O) δ (ppm): 13.2 (C-16), 19.7 (C-15), 21.5 (C-14), 28.3 (C-13), 55.3 (C-4 and C-5), 56.5 (C-12), 69.6 (C-7 and C-10), 78.2 (C-9), 78.7 (C-2 and C-11). MS (ESI+): m/z 225.2120 [C7H14N4+C5H11].
1-hexyl-1,3,6,8-tetraazatricyclo[188.8.131.52,8]undecan-1-ium iodide (3f)
Was isolated as a white solid hygroscopic, (0.330 g, 90%), M.p. = 133-134°C (decomposition), FT-IR (KBr) vmax: 2957, 2935, 2874, 1459, 1407, 1389, 1345, 1321, 1264, 1225, 1163, 1110, 1046, 1031, 1007, 971, 942, 879, 819, 783, 743, 655, 449 cm-1. 1H NMR (400 MHz, D2O) δ (ppm): 0.96 (t, J = 8.0 Hz, 3H, H-17), 1.39 (m, J = 8.0 Hz, 6H, H-16, H15 and H-14), 1.72 (m, J = 8.0 Hz, 2H, H-13), 2.89 (t, J = 8.0 Hz, 2H, H-12), 3.40 (bs, 4H, H-4 and H-5), 3.93 (d, J = 12.0 Hz, 2H, H-7a and H-10a), 4.54 (d, J = 12.0 Hz, 2H, H-7b and H-10b), 4.65 (d, J = 8.0 Hz, 2H, H-2c and H-11c), 4.85 (s, 2H, H-9), 4.86 (d, J = 8.0 Hz, 2H, H-2d and H-11d). 13C NMR (100 MHz, D2O) δ (ppm): 10.8 (C-17), 18.0 (C-16), 20.0 (C-15), 24.2 (C-14), 28.8 (C-13), 55.3 (C-12, C-4 and C-5), 69.7 (C-7 and C-10), 78.6 (C-9), 78.7 (C-2 and C-11). MS (ESI+): m/z 239.2291 [C7H14N4+C6H13].
Single crystal X-ray measurements
Crystal data for compound 3b, C9H19N4.I, were collected using a Xcalibur Atlas Gemini ultra diffractometer of Oxford Diffraction equipped with Mo tube with graphite monochromator, Mo-Enhanced fiber-optics collimator and CCD detector Atlas. M = 310.2, trigonal, R3, a = 12.8935(3), b = 12.8935(3), c = 18.4328(4) Å, V = 2653.8(1) Å3, Z = 9, Dcalcd = 1.746 g/cm3, X-ray source Mo Kα radiation, k = 0.7107 Å, F(0 0 0) = 1386, colorless prism 0.42 × 0.34 × 0.25 mm. All non-hydrogen atoms were refined with anisotropic thermal parameters, and hydrogen atoms of carbons were kept in an ideal geometry. Isotropic ADP of all hydrogen atoms were fixed as a 1.2 multiple of the Ueq of the parent atom. Crystallographic data (excluding structural factors) have been deposited at the Cambridge Crystallographic Data Centre (CCDC). Copies of the data can be obtained free of charge by writing to the CCDC, 12 Union Road, Cambridge CB2 IEZ, UK. Fax: +44-(0)1223-336033 or e-mail: email@example.com. The CCDC deposition number is CCDC 823082.
We acknowledge the Dirección de Investigación Sede Bogotá (DIB) of Universidad Nacional de Colombia for financial support and the Institutional Research Plan No. AVOZ10100521 of the Institute of Physics and the Project Praemium Academiae of the Academy of Sciences of the Czech Republic. Also, J. S-B. is grateful for a scholarship from Facultad de Ciencias, Universidad Nacional de Colombia.
- Rivera A, Núñez ME, Morales-Ríos MS, Joseph-Nathan P: Preparation of cage amine 1,3,6,8-tetraazatricyclo[184.108.40.206,8]undecane. Tetrahedron Lett. 2004, 45: 7563-7565. 10.1016/j.tetlet.2004.08.123.View ArticleGoogle Scholar
- Rivera A, González-Salas D, Ríos-Motta J, Hernández-Barragán A, Joseph-Nathan P: Preferred hydrogen bonding site of 1,3,6,8-tetraazatricyclo[220.127.116.11,8]undecane (TATU) to hydroquinone. J Mol Struct. 2007, 837: 142-146. 10.1016/j.molstruc.2006.10.039.View ArticleGoogle Scholar
- Rivera A, Nuñez ME, Avella E, Rios-Motta J: An NMR study of sequential intermediates and collateral products in the conversion of 1,3,6,8-tetraazatricyclo[18.104.22.168,8]dodecane (TATD) to 1,3,6,8-tetraazatricyclo[22.214.171.124,8]-undecane (TATU). Tetrahedron Lett. 2008, 49: 2154-2158. 10.1016/j.tetlet.2008.01.091.View ArticleGoogle Scholar
- Rivera A, Moyano D, Maldonado M, Ríos-Motta J, Reyes A: FT-IR and DFT studies of the proton affinity of small aminal cages. Spectrochimica Acta Part A. 2009, 74: 588-590. 10.1016/j.saa.2009.07.009.View ArticleGoogle Scholar
- Rivera A, González-Salas D: Synthesis and characterization of novel triazenes from the reaction of the cyclic aminal 1,3,6,8-tetraazatricyclo[126.96.36.199,8]undecane (TATU) with diazonium ions. Tetrahedron Lett. 2010, 51: 2500-2504. 10.1016/j.tetlet.2010.02.174.View ArticleGoogle Scholar
- Rivera A, Sadat-Bernal J, Ríos-Motta J, Dušek M, Fejfarová K: Structural consequences of anomeric effect in 1,3,6,8-tetraazatricyclo[188.8.131.52,8]undecan-1-ium pentachlorophenolate monohydrate. J Chem Crystallogr. 2011, 41: 591-595. 10.1007/s10870-011-0008-8.View ArticleGoogle Scholar
- Patai S: The Chemistry of the Functional Groups, Supplement F: The Chemistry of amino, nitroso and nitro compounds and their derivatives, Part 2. 1982, John Wiley & Sons, Inc., Chichester, UKGoogle Scholar
- Kazantsev OA, Baruta DS, Shirshin KV, Sivokhin AP, Kamorin DM: Concentration effects in the nucleophilic reactions of tertiary amines in aqueous solutions. Alkylation of amines with ethylene chlorohydrin. Russ J Phys Chem A. 2010, 84: 2071-2076. 10.1134/S0036024410120113.View ArticleGoogle Scholar
- Hati S, Datta D: Anomeric effect and hardness. J Org Chem. 1992, 57: 6056-6057. 10.1021/jo00048a049.View ArticleGoogle Scholar
- Sélambarom J, Monge S, Carré F, Fruchier A, Roque JP, Pavia AA: Contribution of the anomeric effect to the solution and crystal structure of [1S,2S,6S,7S]-1,6-diaza-4,9-dioxa-2,7-dimethoxycarbonylbicyclo[4.4.1]undecane, a condensation product of L-serine methyl ester with formaldehyde. Carbohyd Res. 2001, 330: 43-51. 10.1016/S0008-6215(00)00261-5.View ArticleGoogle Scholar
- Alder RW, Carniero TMG, Mowlam RW, Orpen AG, Petillo PA, Vachon DJ, Weisman GR, White JM: Evidence for hydrogen-bond enhanced structural anomeric effects from the protonation of two aminals, 5-methyl-1,5,9-triazabicyclo[7.3.1]tridecane and 1,4,8,11-tetraazatricyclo[184.108.40.206,8]hexadecane. J Chem Soc Perkin Tran 2. 1999, 589-599.Google Scholar
- Kakanejadifard A, Farnia SMF: Synthesis and X-ray structural determination of new aniline derivatives of 2,4,6,8-tetraazabicyclo[3.3.0]octanes; Anomeric effect in N-C-N moiety and implications of solvent polarity on 1H-NMR patterns. Tetrahedron. 1997, 53: 2551-2556. 10.1016/S0040-4020(96)01143-X.View ArticleGoogle Scholar
- Starks CM: Phase-transfer catalysis. I. Heterogeneous reactions involving anion transfer by quaternary ammonium and phosphonium salts. J Am Chem Soc. 1971, 93: 195-199. 10.1021/ja00730a033.View ArticleGoogle Scholar
- Chong KCW, Sivaguru J, Shichi T, Yoshimi Y, Ramamurthy V, Scheffer JR: Use of chirally modified zeolites and crystals in photochemical asymmetric synthesis. J Am Chem Soc. 2002, 124: 2858-2859. 10.1021/ja016989m.View ArticleGoogle Scholar
- Khramov DM, Bielawski CW: Donor-acceptor triazenes: Synthesis, Characterization, and study of their electronic and thermal properties. J Org Chem. 2007, 72: 9407-9417. 10.1021/jo070789x.View ArticleGoogle Scholar
- Tang T, Coady DJ, Boydston AJ, Dykhno OL, Bielawski CW: Pro-Ionomers: An anion metathesis approach to amphiphilic block ionomers from neutral precursors. Adv Mater. 2008, 20: 3096-3099. 10.1002/adma.200800291.View ArticleGoogle Scholar
- Khramov DM, Lynch VM, Bielawski CW: Heterocyclic carbine-transition metal complex: Spectroscopic and crystallographic analyses of π-back-bonding interactions. Organometallics. 2007, 26: 6042-6049. 10.1021/om700591z.View ArticleGoogle Scholar
- Singh RP, Verma RD, Meshri DT, Shreeve JM: Energetic nitrogen-rich salts and ionic liquids. Angew Chem Int Ed. 2006, 45: 3584-3601. 10.1002/anie.200504236.View ArticleGoogle Scholar
- Murray-Rust P: Crystal and molecular structure of 1,3,6,8-tetraazatricyclo[220.127.116.11,8]dodecane, the 2:1 condensation product of formaldehyde and 1,2-diaminoethane, and the conformation of this system. J Chem Soc Perkin Trans 2. 1974, 1136-1141.Google Scholar
- Frisch MJ, Trucks GW, Schlegel HB, Scuseria GE, Robb MA, Cheeseman JR, Zakrzewski VG, Montgomery JA, Stratmann RE, Burant JC, Dapprich S, Millam JM, Daniels AD, Kudin KN, Strain MC, Farkas O, Tomasi J, Barone V, Cossi M, Cammi R, Mennucci B, Pomelli C, Adamo C, Clifford S, Ochterski J, Petersson GA, Ayala PY, Cui Q, Morokuma K, Malick DK, Rabuck AD, Raghavachari K, Foresman JB, Cioslowski J, Ortiz JV, Baboul AG, Stefanov BB, Liu G, Liashenko A, Piskorz P, Komaromi I, Gomperts R, Martin RL, Fox DJ, Keith T, Al-Laham MA, Peng CY, Nanayakkara A, Challacombe M, Gill PMW, Johnson B, Chen W, Wong MW, Andres JL, Gonzalez C, Head-Gordon M, Replogle ES, Pople JA: GAUSSIAN 98 (Revision A9). 1998, Gaussian Inc Pittsburgh: PAGoogle Scholar
- Glister JF, Vaughan K, Biradha K, Zaworotko MJ: (2S,7R,11S,16R)-1,8,10,17-tetraazapentacyclo-[18.104.22.168,17.02,7.011,16]icosane and its enantiomer. Synthesis, NMR analysis and X-ray crystal structure. J Mol Struct. 2005, 749: 78-83. 10.1016/j.molstruc.2005.03.043.View ArticleGoogle Scholar
- Yang W, Mortier WJ: The use of global and local molecular parameters for the analysis of the gas-phase basicity of amines. J Am Chem Soc. 1986, 108: 5708-5711. 10.1021/ja00279a008.View ArticleGoogle Scholar