Low-temperature X-ray structural studies of the ester and ether derivatives of cis- and trans-4-tert-butyl cyclohexanol and 2-adamantanol: application of the variable oxygen probe to determine the relative σ-donor ability of C–H and C–C bonds

2003 ◽  
Vol 1 (17) ◽  
pp. 3094-3101 ◽  
Author(s):  
Marisa Spiniello ◽  
Jonathan M. White
Keyword(s):  
Low Temperature ◽  
Structural Studies ◽  
Oxygen Probe ◽  
X Ray ◽  
Tert Butyl ◽  
Donor Ability ◽  
Cis And Trans ◽  
Derivatives Of

Application of the Variable Oxygen Probe to Determine the π-Electron Donor Ability of the Alkyne Group

2014 ◽  
Vol 67 (12) ◽  
pp. 1866 ◽  
Author(s):  
Benjamin L. Harris ◽  
Jonathan M. White
Keyword(s):  
Low Temperature ◽  
Electron Donor ◽  
Oxygen Probe ◽  
X Ray ◽  
X Ray Crystallography ◽  
Donor Ability ◽  
Structural Database ◽  
Derivatives Of ◽  
Electron Demand ◽  
Electron Donor Ability

Eight ester and ether derivatives of propargyl alcohol with varying electron demand were structurally characterised using low temperature X-ray crystallography, these were combined with seven derivatives obtained from the Cambridge Structural Database. Variable oxygen probe analysis of these derivatives provided evidence that the ethynyl substituent is a relatively weak π-electron donor, and is a slightly less effective donor than the C–C bond of an ethyl substituent.

Gauging the Donor Ability of the C-Si Bond. Results from Low-Temperature Structural Studies of gauche and Antiperiplanar β-Trimethylsilyl-cyclohexyl Esters and Ethers by Use of the Variable Oxygen Probe.

2000 ◽  
Vol 53 (4) ◽  
pp. 285 ◽  
Author(s):  
Alison J. Green ◽  
Josie Giordano ◽  
Jonathan M. White
Keyword(s):  
Low Temperature ◽  
Bond Distance ◽  
Structural Studies ◽  
Oxygen Probe ◽  
Pka Value ◽  
Donor Ability ◽  
Derivatives Of

A plot of C–OR bond distance against pKa(ROH) for esters and ether derivatives of the antiperiplanar β-silyl alcohol (4) has a slope of –5.310–3. This represents a stronger response of the C–OR distance than was observed for the corresponding gauche β-silyl alcohol (5) and its derivatives. This result is consistent with the greater donor ability of a C–Si bond compared with a C–C bond. Comparison of these plots with those previously reported for derivatives (3) of tetrahydropyran-2-ol reveals that a C–Si bond is a weaker donor than an oxygen non-bonded pair of electrons. An estimate of the pKa value for 2,4-dinitrobenzenesulfenic acid (14) was derived from these plots.

Probing the Ground-State δ Effect of Group 14 Metal Substituents. X-Ray Structures of cis- and trans-4-Trimethylmetal-Substituted Cyclohexyl p-Nitrobenzenesulfonates

1998 ◽  
Vol 51 (7) ◽  
pp. 555 ◽  
Author(s):  
Alison J. Green ◽  
Victor Van ◽  
Jonathan M. White
Keyword(s):  
Low Temperature ◽  
Ground State ◽  
Structural Studies ◽  
Structural Effects ◽  
Group 14 ◽  
X Ray ◽  
Bond Interaction ◽  
Cis And Trans

Accurate low-temperature X-ray structural studies on trans-4-trimethylsilylcyclohexyl p-nitrobenzene- sulfonate (31) and cis- and trans-4-trimethylstannylcyclohexyl p-nitrobenzenesulfonates (32) and (33) failed to demonstrate the presence of any significant structural effects due to a σM-C-σC-C-σ*C-O through-bond interaction between the C–M σ donor orbital and the σ*C-ONs acceptor orbital.

The Through-Bond Interaction of a Sulfur Lone Pair with Oxygenated Substituents in the Thiacyclohexane Framework

2005 ◽  
Vol 58 (7) ◽  
pp. 531
Author(s):  
Laura Andrau ◽  
Jonathan M. White
Keyword(s):  
Low Temperature ◽  
Crystal Structures ◽  
Bond Distance ◽  
Lone Pair ◽  
X Ray ◽  
Ester Derivative ◽  
Bond Interaction ◽  
Derivatives Of ◽  
Electron Demand

Low-temperature X-ray crystal structures were determined on a range of derivatives of 4-thiacyclohexanol 5a of varying electron demand with a view to finding evidence for a through-bond interaction between the sulfur lone pair and the oxygenated substituent. In contrast to earlier suggestions, plots of C–OR bond distance versus pKa (ROH) showed that any interaction between the sulfur and the OR group is unlikely to be of a through-bond origin. Furthermore, unimolecular solvolysis rate measurements on the nosylate ester derivative 5g showed that the sulfur actually retards the reaction slightly in comparison with the corresponding sulfur-free analogue 6.

Structural studies on monofluorinated derivatives of the phytohormone indole-3-acetic acid (auxin)

1996 ◽  
Vol 52 (4) ◽  
pp. 651-661 ◽  
Author(s):  
A. Antolić ◽  
B. Kojić-Prodić ◽  
S. Tomić ◽  
B. Nigović ◽  
V. Magnus ◽  
...  
Keyword(s):  
Acetic Acid ◽  
Side Chain ◽  
Structural Studies ◽  
X Ray Diffraction ◽  
Molecular Conformations ◽  
X Ray ◽  
Structure Activity ◽  
Planar Conformation ◽  
Derivatives Of ◽  
Indole 3 Acetic Acid

As part of the molecular recognition studies on the phytohormone indole-3-acetic acid (IAA) a series of fluorinated IAA's has been examined. The phenyl ring substitution at positions 4, 5, 6 and 7 resulted in four compounds, which were analyzed. Structure–activity correlation includes the analysis of their molecular conformations, based on the X-ray diffraction and computational chemistry results, and bioactivity determinations in the Avena coleoptile and the Pisum sativum stem straight-growth tests, lipophilicity and UV absorbance. The conformations of monofluorinated IAA's and a free hormone are defined by rotations about two bonds: one describes the relative orientation of a side chain towards the indole plane and the second the orientation of the carboxylic group. The results of X-ray structure analysis revealed the folded shape of the molecules in all compounds studied. Molecular mechanics and dynamics located the folded conformation as the local minimum, but failed to detect the planar conformation as one of the local minima, which according to ab initio results on IAA and 4-CI-IAA could also be possible. Crystal data at 295 K for 4-F-IAA and at 297 K for 5-F-IAA, and at 100 K for 6-F-IAA and 7-F-IAA using Mo Kα radiation (λ = 0.71073 Å) and Cu Kα (λ = 1.5418 Å, for 7-F-IAA), are as follows: 4-F-IAA, C10H8NO2F, Mr = 193.18, monoclinic, C2/c, a = 17.294 (5), b = 13.875 (4), c = 7.442 (4) Å, β = 103.88 (6)°, V = 1734 (1) Å3, Z = 8, Dx = 1.480 g cm−3, μ = 1.1 cm−1, F(000) = 800, R = 0.043, wR = 0.044 for 823 symmetry-independent [I ≥ 3σ(I)] reflections; 5-F-IAA, C10H8NO2F, monoclinic, P21/c, a = 19.284 (5), b = 5.083 (4), c = 9.939 (4) Å, β = 117.28 (6)°, V = 865.9 (1) Å3, Z = 4, Dx = 1.482 g cm−3, μ = 1.1  cm−1, F(000) = 400, R = 0.062, wR = 0.057 for 729 symmetry-independent [I ≥ 3σ(I)] reflections; 6-F-IAA, C10H8NO2F, monoclinic, P21/a, a = 9.360 (1), b = 5.167 (4), c = 17.751 (4) Å, β = 93.75 (1)°, V = 856.7 (8) Å3, Z = 4, Dx = 1.498 g cm−3, μ = 1.1 cm−1, F(000) = 400, R = 0.048, wR = 0.048 for 1032 symmetry-independent [I ≥ 2σ(I)] reflections; 7-F-IAA, C10H8NO2F, monoclinic, P21/a, a = 9.935 (5), b = 5.0059 (4), c = 17.610 (1) Å, β = 102.13 (1)°, V = 856.3 (1) Å3, Z = 4, Dx = 1.498 g cm−3, μ = 9.8 cm−1 (Cu Kα, F(000) = 400, R = 0.035, wR = 0.040 for 1504 symmetry-independent [I ≥ 2σ(I)] reflections.

Influence of Trimethylsilyl Substituents on Primary C - O Bond Lengths at the b-Position: Results from Low-Temperature X-Ray Structural Studies

1997 ◽  
Vol 50 (9) ◽  
pp. 927 ◽  
Author(s):  
Alison J. Green ◽  
William Issa ◽  
Jonathan M. White
Keyword(s):  
Low Temperature ◽  
Ester Bond ◽  
Structural Studies ◽  
Structural Effects ◽  
X Ray ◽  
Bond Lengths

The β-trimethylsilyl substituent in 2-trimethylsilylethyl p-nitrobenzoate (12b) and 2-trimethylsilylethyl 2,4-dinitrobenzenesulfenate (12c) leads to significant lengthening of the C(alkyl)–O(ester) bond. Lengthening of the Si-CH2 distance in the more electronegative ester (12c) relative to (12b) is also observed. These structural effects are consistent with the presence of σC-Si–σ* C-O interactions.

Derivatives of 1,3,5-Triamino-1,3,5-trideoxy-cis-inositol as Versatile Pentadentate Ligands for Protein Labeling with Re-186/188. Prelabeling, Biodistribution, and X-ray Structural Studies

1998 ◽  
Vol 9 (6) ◽  
pp. 691-702 ◽  
Author(s):  
Andreas Kramer ◽  
Roger Alberto ◽  
André Egli ◽  
Ilse Novak-Hofer ◽  
Kaspar Hegetschweiler ◽  
...  
Keyword(s):  
Protein Labeling ◽  
Structural Studies ◽  
X Ray ◽  
Pentadentate Ligands ◽  
Derivatives Of

Cobalt(II) and nickel(II) complexes of some bidentate imidazoline ligands. Stereochemically dependent derealization in the imidazoline rings

1970 ◽  
Vol 48 (19) ◽  
pp. 3076-3088 ◽  
Author(s):  
A. B. P. Lever ◽  
B. S. Ramaswamy ◽  
S. H. Simonsen ◽  
L. K. Thompson
Keyword(s):  
Double Bond ◽  
Low Temperature ◽  
Room Temperature ◽  
X Ray ◽  
Cis And Trans ◽  
Imidazoline Ring

Tetrahedral and octahedral cobalt(II), and square and octahedral nickel(II) complexes of 1,2-bis(2′-imidazolin-2′-yl)benzene, 1,2-bis(2′-imidazolin-2′-yl)ethane, and some imidazoline ring methyl substituted ligands are reported. The structures are confirmed by three X-ray structural analyses, magnetism, and electronic and vibrational (conventional and far i.r.) spectroscopy. Both cis and trans octahedral complexes of the type M(ligand)2(NCS)2 [M = Co(II), Ni(II)] have been characterized, and none of these exhibit splitting of the v(CN)(NCS) absorption in the i.r. spectrum at room temperature. Low temperature studies reveal splitting of the v(CN) band in the cis isomers. Both 13C and 15N satellite absorption is identified. The delocalization of the double bond in the imidazoline rings in these complexes is discussed in terms of the i.r. and X-ray data.

Molecular structure and substituent electronic effects in 10-arylidenanthrones-9

2000 ◽  
Vol 215 (5) ◽  
Author(s):  
O.V. Shishkin ◽  
A.Yu. Kovalevsky ◽  
M. Yu. Antipin ◽  
Z.N. Tarakhno
Keyword(s):  
Gas Phase ◽  
Phenyl Group ◽  
Conformational Flexibility ◽  
Am1 Method ◽  
Equilibrium Geometry ◽  
Boat Conformation ◽  
Structural Studies ◽  
Electronic Effects ◽  
X Ray ◽  
Derivatives Of

X-ray structural studies of derivatives of 10-arylidenanthrone-9 containing π-electron donating and withdrawing substituents within arylidene fragment have been carried out. In the crystal the molecules are strongly disflattened with the central dihydrocycles adopting an asymmetric boat conformation. This geometry of the molecules is a result of unfavourable non-valence interactions between atoms at the C=C bond and the hydrogens at the peri-positions of the anthraquinone fragment. Calculations performed by the semiempirical quantum-chemical AM1 method demonstrate that in the gas phase equilibrium geometry of the molecules was similar to that in the crystal. It was shown as well that the central dihydrocycle possesses high conformational flexibility in spite of steric overcrowding in all of the compounds. Electronic effects of the substituents had significant influence only on the arylidene moiety, resulting in different rotation angles of the phenyl group around the C=C exocyclic bond and virtually no effect on the anthraquinone part of the molecules.

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