Conformational analysis, part 43. A theoretical and LIS/NMR investigation of the conformations of substituted benzamides

Abraham, Raymond J.; Aboitiz, Nuria; Filippi, Marco; Genesio, Eva; Piaggio, P.; Sancassan, Fernando

doi:10.1002/mrc.4243

Cited by 6 publications

(8 citation statements)

References 38 publications

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“…Fluorine poses considerable problems in quantum mechanics and molecular modelling, the greater stability of cis vs. trans difluoroethylene being a classic case. 35 More recently we have commented on the small H-bonding energy in NHÁ Á ÁF 36 and OHÁ Á ÁF 37 interactions compared to quantum mechanical calculations. It is therefore of some interest to determine whether these results are supported by other physical measurements.…”

Section: Discussionmentioning

confidence: 99%

A re-investigation of ⁴J_FF and ⁵J_FF nuclear spin–spin couplings in substituted benzenes, a novel conformational tool

Abraham

Cooper

2016

Phys. Chem. Chem. Phys.

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A theoretical analysis of the (4)JFF and (5)JFF couplings in fluorobenzenes separates the σ and π components of the substituent coefficients. The π bond mechanism is dominant but the σ bond mechanism must be included to give accurate values of the couplings. For monosubstituted difluorobenzenes the (4)JFF and (5)JFF couplings can be predicted from the calculated π densities by linear equations. The use of additive substituent effects allows the prediction of the meta(4)JFF couplings for multisubstituted compounds. The π dependence of the (4)JFF coupling in 2,6-difluorobenzenes provides a novel and simple method of determining the torsional angle of the C1 substituent and the benzene ring for non-symmetrical functional groups (acetyl, carboxymethyl, dimethylamino, amide, nitro etc.). This could be used to determine the geometries of such molecules in biological systems. The π dependence of the (4)JFF coupling is also of importance in the charged species of 2,6-difluoroanilinium ((4)JFF 2.1 Hz) and 2,6-difluoro-N,N,N-trimethylanilinium ((4)JFF 0.0 Hz) due to the very different π electron densities.

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Section: Discussionmentioning

confidence: 99%

A re-investigation of ⁴J_FF and ⁵J_FF nuclear spin–spin couplings in substituted benzenes, a novel conformational tool

Abraham

Cooper

2016

Phys. Chem. Chem. Phys.

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“…Abraham et al recently performed lanthanoid induced shift (LIS) NMR experiments on various amide containing organic molecules which showed that when a lanthanoid is complexed to the carbonyl oxygen of the amide moiety, pNMR shifts of 30-40 ppm can be achieved. 107 The cis proton was shifted significantly more than the trans proton, which is intuitive because the LIS paramagnetism is almost purely dipolar in nature and the lanthanoid distance to the cis proton was shorter than the distance to the trans proton. In the optimized structure of the paraCEST iron complex (FeL 3 ) 2+ the distances of the two protons from the paramagnetic iron center are also different, 4.55 for cis and 4.95 for trans, but this is not the cause of the observed shift difference.…”

Section: Application To Iron Paracest Complexesmentioning

confidence: 97%

Kohn–Sham calculations of NMR shifts for paramagnetic 3d metal complexes: protocols, delocalization error, and the curious amide proton shifts of a high-spin iron(ii) macrocycle complex

Martin

Autschbach

2016

Phys. Chem. Chem. Phys.

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A theory for the nuclear chemical shifts of molecules in arbitrary spin states is applied to a set of paramagnetic organometallic complexes of 3d metals. Ligand chemical shifts are calculated and analyzed using Kohn-Sham (KS) density functional theory with and without relativistic corrections. The roles of the KS delocalization error, Gaussian-type versus Slater-type basis sets, relativistic effects (scalar and spin-orbit), and zero field splitting (ZFS) are investigated. A strong functional dependence of the chemical shifts is apparent and correlated with the delocalization error. The functional dependence is between one and two orders of magnitude larger than variations of the NMR shifts due the other influences that are investigated. ZFS effects are negligible in the determination of the NMR chemical shifts of the complexes except at very low temperatures. The DFT calculated shifts agree reasonably well with experiment. A 73 ppm difference in the NMR shifts of the two protons in the amide groups of a high-spin Fe(ii) macrocycle complex arises from selective O → Fe dative bonding that only involves the transfer of β spin density, along with orbital delocalization throughout the ligand bonding framework which electronically couples the coordinating oxygen lone pair orbitals directly to the amide trans proton.

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“…The proposed mechanism proceeds through a ternary complex in which the trifluoroacetamidopyrazole ligand of Λ- Ir2 forms a double hydrogen bond with the nitroalkene, whereas one N , N -diethylcarboxamide moiety accepts a hydrogen bond from the indole NH group. Due to steric repulsion, the two ethyl groups force the carboxamide to rotate out of conjugation with the benzothiazole moiety . While multiple conformations are possible, only one leads to a catalytically productive ternary complex, and this conformational flexibility must be entropically unfavorable.…”

Section: Resultsmentioning

confidence: 99%

Restricted Conformation of a Hydrogen Bond Mediated Catalyst Enables the Highly Efficient Enantioselective Construction of an All-Carbon Quaternary Stereocenter

Shen

et al. 2016

ACS Catal.

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All reactions were carried out under an atmosphere of argon with magnetic stirring. Solvents were distilled under argon from calcium hydride (CH3CN and CH2Cl2) or sodium/benzophenone (Et2O, THF and toluene). Iridium catalyst Λ-Ir1, 1 pyridylpyrazole L1, 1 bispyrazole L2 2 and the β,β-disubstituted nitroalkene substrates 1,3,4 were prepared according to published procedures. All other reagents were purchased from commercial suppliers (TCI, Aldrich, Alfa and J&K) and used without further purification. Column chromatography was performed with silica gel from Huanghai Chemical Reagent (300-400 mesh). 1 H and 13 C NMR spectra were recorded on a Bruker AM ( 400MHz or 500 MHz) spectrometer at ambient temperature. NMR standards were used as follows: ( 1 H NMR) CDCl3 = 7.26 ppm, CD2Cl2 = 5.32 ppm; ( 13 C NMR) CDCl3 = 77.0 ppm, CD2Cl2 = 53.8 ppm.IR spectra were recorded on a Nicolet Avatar 330 FT-IR spectrophotometer. Chiral HPLC chromatograms were obtained from an Agilent 1260 Series HPLC system. CD spectra were recorded on a JASCO J-810 CD spectropolarimeter (600-200 nm, 1 nm band width, 50 nm/min scanning speed, accumulation of 3 scans). High-resolution mass spectra were recorded on a Bruker En Apex Ultra 7.0T FT-MS instrument using ESI technique. Enantiomeric excess (ee) values of the products were determined by HPLC on chiral phase. S3 Preparation of the Iridium Catalysts Synthesis of the Cyclometalating Ligands L3 and (R)-L4Scheme S1. Synthetic route to the cyclometalating ligand L3.A suspension of 9H-carbazole (7.26 g, 60.0 mmol) and K2CO3 (41.46 g, 300.0 mmol) in DMSO (150 mL) was stirred at room temperature for 1 h. 2-Fluorobenzonitrile (10.03 g, 60.0 mmol) was added and stirred at 150 °C overnight. After cooled to room temperature, the reaction mixture was poured into ice water (300 mL). Then the reaction mixture was extracted with ethyl acetate (3 x 100 mL). The combined organic layer was washed with brine (3 x 200 mL) and then dried over anhydrous Na2SO4, filtered and concentrated in vacuo. The residue was washed by the mixture of n-hexane and ethyl acetate (v/v = 20/1, 3 x 50 mL) to afford the compound S1 as a white solid (14.71 g, 54.9 mmol, 91% yield).

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Conformational analysis, part 43. A theoretical and LIS/NMR investigation of the conformations of substituted benzamides

Cited by 6 publications

References 38 publications

A re-investigation of ⁴J_FF and ⁵J_FF nuclear spin–spin couplings in substituted benzenes, a novel conformational tool

A re-investigation of ⁴J_FF and ⁵J_FF nuclear spin–spin couplings in substituted benzenes, a novel conformational tool

Kohn–Sham calculations of NMR shifts for paramagnetic 3d metal complexes: protocols, delocalization error, and the curious amide proton shifts of a high-spin iron(ii) macrocycle complex

Restricted Conformation of a Hydrogen Bond Mediated Catalyst Enables the Highly Efficient Enantioselective Construction of an All-Carbon Quaternary Stereocenter

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Conformational analysis, part 43. A theoretical and LIS/NMR investigation of the conformations of substituted benzamides

Cited by 6 publications

References 38 publications

A re-investigation of 4JFF and 5JFF nuclear spin–spin couplings in substituted benzenes, a novel conformational tool

A re-investigation of 4JFF and 5JFF nuclear spin–spin couplings in substituted benzenes, a novel conformational tool

Kohn–Sham calculations of NMR shifts for paramagnetic 3d metal complexes: protocols, delocalization error, and the curious amide proton shifts of a high-spin iron(ii) macrocycle complex

Restricted Conformation of a Hydrogen Bond Mediated Catalyst Enables the Highly Efficient Enantioselective Construction of an All-Carbon Quaternary Stereocenter

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A re-investigation of ⁴J_FF and ⁵J_FF nuclear spin–spin couplings in substituted benzenes, a novel conformational tool

A re-investigation of ⁴J_FF and ⁵J_FF nuclear spin–spin couplings in substituted benzenes, a novel conformational tool