Molecular mechanics calculations for ethers. The conformations of some crown ethers and the structure of the complex of 18-crown-6 with benzylammonium thiocyanate

Bovill, Moira J.; Chadwick, Derek J.; Sutherland, I. O.; Watkin, David

doi:10.1039/p29800001529

Cited by 113 publications

(57 citation statements)

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“…Recently reported molecular-mechanics calculations of ethers (Bovill, Chadwick, Sutherland & Watkin, 1980) showed the commonly observed D3d conformation of 18-crown-6 to be 11.85 kJ mo1-1 less stable than the biangular conformation. The relatively high steric energy is mostly due to the arrangement of O atoms (mean distance ca 2.8A) resulting in unfavourable dipole interactions.…”

Section: Discussionmentioning

confidence: 99%

“…Dunitz, Dobler, Seiler & Phizackerley, 1974), the ligand usually adopts a conformation with approximate D3d symmetry, e.g. with dimethyl acetylenedicarboxylate (Goldberg, 1975), malononitrile (Kaufmann, Kn6chel, Kopf, Oehler & Rudolph, 1977), NH4 + (Nagano, Kobayashi & Sasaki, 1978), benzylammonium (Bovill, Chadwick, Sutherland & Watkin, 1980), 2,4-dinitrophenylhydrazine (Hilgenfeld & Saenger, 1981) and p-nitroaniline (Weber, 1981). Recently reported structures of adducts with urea (Harkema, van Hummel, Daasvatn & Reinhoudt, 1981) …”

Section: Anorganisch-chemisches Institut Der Universitdtmentioning

confidence: 99%

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A 2:1 complex of 4-nitro-1,2-benzenediamine and 1,4,7,10,13,16-hexaoxacyclooctadecane (18-crown-6)

Weber¹

1982

Acta Crystallogr B Struct Crystallogr Cryst Chem

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Section: Discussionmentioning

confidence: 99%

Section: Anorganisch-chemisches Institut Der Universitdtmentioning

confidence: 99%

A 2:1 complex of 4-nitro-1,2-benzenediamine and 1,4,7,10,13,16-hexaoxacyclooctadecane (18-crown-6)

Weber¹

1982

Acta Crystallogr B Struct Crystallogr Cryst Chem

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“…In the crystalline state, the conformation of uncomplexed 18-crown-6 differs substantially [21] from the approximate Dßa symmetry found in the current structure for both the crown molecules (Table IV) and also in most complexes of 18-crown-6 with 'fitting' cationic e~ Table II (4) 1 Refers to the symmetry ' operation -x, 1 --y. 1-2; 2 to --x, 1 -y, -acceptors such as alkaline metal ions [22] or NH<i + [15] and R-NH3+ [14]. A conformational disorder of the crown molecules (as a consequence of the existence of non-coordinating macrocycles in the lattice) or at least extremely anisotropic movement of its atoms might therefore have been expected but was not obvious, probably due to packing forces.…”

Section: Resultsmentioning

confidence: 99%

“…2522 (2) 3567 (2) 3746 (1) 73 1)* C (2) 2378 (3) 2019 (3) 3902 (2) 82 1)* C (3) 743 (3) 1686 (3) 3828 (2) 78 1)* 0(4) -300 (2) 2086 (2) 4645 (1) 73 1)* 0 (5) -1902 (4) 1953 (3) 4568 (2) 84 1)* C (6) -2940 (3) 2362 (3) 5454 (2) 87 1)* 0 (7) -3036 (2) 3907 (2) 5390 (1) 78 1)* 0 (8) -4024 (3) 4403 (3) 6205 (2) 90 1)* 0 (9) -3984 (3) 6023 (3) 6104 (2) 89 1)* 0 (10) 2850 (2) 5731 (2) 406 (1) 78 1)* 0 (11) 3409 (3) 4865 (3) 1211 (2) 82 1)* 0 (12) 3398 (3) 3281 (3) 1112 (2) 79 1)* 0 (13) 1819 (2) 2846 (2) 1266 (1) 74 1)* 0 (14) 1679 (3) 1389 (3) 1123 (2) 82 1)* 0 (15) 9 (3) 1084 …”

Section: Methodsunclassified

“…It is normally found with highly symmetrical cationic e -acceptor groups such as R-NH3+ [14] or NH4+ [15], possibly due to additional interactions of the positive N atom with the lone pairs of those crown 0 atoms not coordinating to H atoms [16]; with the (neutral) CH3 groups of dimethylsulphone [17], however, and with one R-NH2^ group of guanidinium nitrate [18] 1:2 adducts were obtained.…”

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A 1:1 Host-Guest Complex between 1,4,7,10,13,16-Hexaoxacyclooctadecane ('18-crown-6') and m-Nitroaniline: Mere Stoicheiometry or a Genuine 1:1 Adduct ?

Weber

1982

Zeitschrift Für Naturforschung B

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Abstract The stoicheiometrically 1:1 adduct of 1,4,7,10,13,16-hexaoxa-cyclooctadecane with m-nitroaniline, C18H30N2O8, Mr = 402.45, crystallises from toluene in red-orange prisms, (probable) space group P1̄, a = 801.8(3), b = 920.4(3), c = 1403.3(4) pm, α = 80.40(4), β = 79.79(4), γ = 85.95(3)°, V = 1.07910 nm3 , Z = 2, dcalc. = 1.238 Mgm-3 . Structure refinement converged at R = 0.060 (Rw = 0.002) for 2915 diffractometer data.

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Crown Ether–Ammonium Complexes: Binding Mechanisms and Solvent Effects

Rüdiger

Schneider²,

Solov'ev

et al. 1999

Eur. J. Org. Chem.

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Thermodynamics of 18‐crown‐6 complexes with ammonium cations (NH4, MeNH3, Me2NH2, Me3NH, Me4N, Et4N, PhNH3, and PhCH2NH3 ) in methanol were determined by titration calorimetry. The results show strong contributions from entropy terms counteracting the enthalpy of complexation, and a linear decrease of the complexation free energy ΔG with the number of available N–H hydrogen bonds. In several cases formation of relatively strong complexes containing two ammonium ions per crown unit was observed. Tetramethylammonium ions show no detectable association with the crown ether, demonstrating the absence of significant Coulomb‐type interaction between the partial charges at the crown ether oxygen and the N+–C–H atoms. Ammonium ions bind to aza crown ethers with almost equal affinity as to the all‐oxygen anologs only, if methyl groups at the nitrogen atoms force the lone pairs into equatorial position. Molecular mechanics calculations (CHARMm) of corresponding gas‐phase complexes yield geometries and energies in agreement with this, with energetically equally good conformations of an essentially undistorted D3d crown accepting either 3 linear hydrogen bonds, or 6 bifurcated bonds from the primary ammonium cations. Complexation equilibria were measured with PhNH3, and PhCH2NH3 in water, 2‐propanol, tert‐butyl alcohol, n‐octanol, DMF, DMSO, pyridine, HMPT and acetone mostly by calorimetry, in some cases by potentiometry. The observed association constants varied by factors of up to 1000; the solvent effects can be described generally as a linear function of the hydrogen bond accepting power of the solvent molecules, in line with the mechanisms derived above. The lgK and ΔH values of the complexation of the PhNH3 or PHCH2NH3 cation with 18‐crown‐6 ligand are compared with a large range of available solvent properties. The best correlations (R ≈ 0.9) for lgK (or ΔG) are obtained with values characterizing the electron donor capacity of the solvent (Ca, β*, DN) for lgK, as found earlier for complexes between K+ and 18C6.

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Molecular mechanics calculations for ethers. The conformations of some crown ethers and the structure of the complex of 18-crown-6 with benzylammonium thiocyanate

Cited by 113 publications

References 1 publication

A 2:1 complex of 4-nitro-1,2-benzenediamine and 1,4,7,10,13,16-hexaoxacyclooctadecane (18-crown-6)

A 2:1 complex of 4-nitro-1,2-benzenediamine and 1,4,7,10,13,16-hexaoxacyclooctadecane (18-crown-6)

A 1:1 Host-Guest Complex between 1,4,7,10,13,16-Hexaoxacyclooctadecane ('18-crown-6') and m-Nitroaniline: Mere Stoicheiometry or a Genuine 1:1 Adduct ?

Crown Ether–Ammonium Complexes: Binding Mechanisms and Solvent Effects

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