CH2 Protons Research Articles

Structure Determination of Diastereoisomeric Thia-Michael Bis-adducts of Methyl (5-Methylidene-4-oxocyclopent-2-en-1-yl)acetate with Ethanethiol

Three of the four possible diastereoisomeric thia-Michael addition products of the reaction of methyl (5-methylidene-4-oxo-cyclopent-2-en-1-yl)acetate with ethanethiol have been isolated and characterized. The major diastereoisomer is all-trans, while the overall fraction of the minor cis,trans and trans,cis isomers does not exceed 30%. The diastereoisomer structure has been determined on the basis of characteristic coupling constants of CH protons of the cyclopentane ring in the 1H NMR spectra.

Effect of triglyceride glycerol CH signal on olefinic resonance quantification with proton magnetic resonance spectroscopy at 3 T

The in-vivo Magnetic Resonance Spectroscopy (MRS) techniques STimulated Echo Acquisition Mode (STEAM) and Point RESolved Spectroscopy (PRESS) are used to assess fat unsaturation levels in human adipose tissue by measuring the olefinic proton resonance at ≈5.4 ppm. At clinical field strengths, the resonance is overlapped by that of the triglyceride glycerol CH proton at ≈5.2 ppm. In the presented work, olefinic resonance contamination by that of the glycerol CH proton for STEAM and PRESS as a function of echo time (TE) is assessed at 3 T. MRS spectra were acquired from the triglyceride tricaprylin (contains glycerol but no olefinic protons), and from free oleic acid (contains olefinic but no glycerol protons) using STEAM (TE of 20 to 300 ms, mixing time of 20 ms) and PRESS (TE of 40 to 300 ms), with TE increments of 10 ms. Estimated olefinic signal contamination by the glycerol CH resonance was evaluated for short-TE (STEAM with TE of 20 ms and PRESS with TE of 40 ms) for human adipose tissue based on a literature composition and using the spectra acquired for tricaprylin and oleic acid. Contaminations of ≈20% for STEAM with a TE = 20 ms and ≈13% for PRESS with a TE = 40 ms were obtained. Glycerol CH contributions to the olefinic resonance was also estimated for eight oils in a similar manner. High-resolution in-vitro 16.5 T Nuclear Magnetic Resonance (NMR) spectra of the oils suggest that in the absence of significant T2 relaxation and J-coupling effects, 9 to 17% (depending on unsaturated fatty acid content) of the olefinic signal is attributable to the glycerol CH proton. The signal yield responses of the glycerol CH and the olefinic protons as a function of TE indicate that a TE of 90 ms for STEAM and a TE of 200 ms for PRESS are suitable for quantification of the olefinic resonance with minimal impact from the glycerol CH resonance. Signal area yields relative to those obtained with short-TE were 30% and 29% for the olefinic resonance and 4% and 5% for the glycerol resonance for STEAM with a TE of 90 ms and PRESS with a TE of 200 ms, respectively. The efficacy of the timings was verified in vivo on tibial bone marrow.

Spin-torsion dominated hyperfine splittings in the first excited torsional state (vt = 1) of methanol

Doublet, triplet and quartet hyperfine splitting patterns have been observed in the E-species component of the first excited (vt = 1) torsional state of CH3OH. Four series of lines dominate the available data: (i) a K = 6 ← 7, Q branch series of quartets, with 7 ≤ J ≤ 15; (ii) a K = 3 ← 2, Q branch series, with 3 ≤ J ≤ 18, which starts as quartets, changes to doublets at J = 7, and then finally to singlets at J = 17; (iii) a K = −2 ← −3, P branch series of doublets, with 8 ≤ J ≤ 13; and (iv) a K = 8 ← 7, Q branch series, with 8 ≤ J ≤ 24, which starts as triplets and becomes doublets at J = 12. There are also a few isolated doublets and quartets, which do not form long spectroscopic branches. We have modeled the hyperfine quartet and doublet splittings with empirically chosen symmetry-allowed spin-torsion, spin-rotation, and spin–spin interaction terms appropriate for the two I = ½ spin systems arising from the OH proton and from the CH3 protons, respectively, and have achieved a least-squares fit of 144 hyperfine components (88 hyperfine intervals) to six hyperfine parameters with a standard deviation (0.75 kHz) near experimental measurement accuracy. The three spin-rotation parameters associated with one I = ½ spin system in the fit agree well with ab initio predictions for IOH parameters in the literature. The two spin-torsion parameters agree to some extent with other fitted values in the literature. The physical effects included in the present Hamiltonian differ from those included in the Hamiltonian for our earlier work on hyperfine splittings in vt = 0 E states, because the experimentally observed vt = 1 splittings are found to decrease approximately as 1/J, whereas the vt = 0 splittings increase approximately as J. The position and relative intensities of the weak central features of the triplets are explained as three-level Λ-type crossover resonances.

First Synthesis of Aliphatic Nitro‐NNO‐azoxy Compounds

The first aliphatic nitro‐NNO‐azoxy compounds were synthesized by substitutive nitration of appropriate tert‐butyl‐NNO‐azoxy compounds with nitronium tetrafluoroborate. Nitro(nitro‐NNO‐azoxy)methane (1), (tert‐butyl‐NNO‐azoxy)(nitro‐NNO‐azoxy)methane (2), bis(nitro‐NNO‐azoxy)methane (3), and 2‐nitro‐2‐(nitro‐NNO‐azoxy)propane (4) were prepared. Compound 4 with the nitro‐NNO‐azoxy group bound with the tertiary C atom appeared most stable (DSC, onset temperature of decomposition 104 °C). Compound 2 was less stable (DSC, onset temperature 88 °C). Compounds with strong electron withdrawing substituents had the least stability, assumingly, due to rather high acidity of CH protons alongside with instability of C‐anions of nitro‐NNO‐azoxy compounds.

Synthesis of noval chiral tridentate amino alcohols as chiral solvating agents under ball-milling conditions

A new family of chiral solvating agents based on chiral didentate amino alcohols and chloromethyl pyridine derivatives were synthesized by ball milling in solvent free condition. The new chiral tridentate amino alcohols were tested as chiral NMR solvating agents for the Ts-derivatives of amino acids, other several acids and pyrazole drugs. For the Ts-derivatives of amino acids studied herein, chiral tridentate amino alcohol 3a could be used for the assignment of the absolute configurations of their racemes through the chemical shift non-equivalences of their CH3 (Ts) protons with certain confidence.

A new ferrocenophane with amide and triazole donors for recognition of dihydrogenphosphate anion

A new ferrocenophane 1 incorporation amide and triazole donors has been conveniently prepared via ‘click’ reactions in the cyclization step. The probe shows exclusive electrochemical sensing of H2PO4− with a large potential shift. The 1H NMR titrations and DFT calculation results show that the amide NH, the triazole CH, the endocyclic benzene CH and the α-position cyclopentadiene CH protons of 1 play a key role for binding with the guest H2PO4− anion.

Synthesis, characterization, and drug release activity of structurally modified poly(vinyl alcohol)

ABSTRACTThe main aim of the present investigation is synthesis of drug‐grafted poly(vinyl alcohol) (PVA) for sustainable drug release in order to avoid bulk release and unwanted side effects. Here, the PVA was structurally modified with five different drug molecules in DMSO medium at 85 °C under N2 atmosphere for 2 h. The structure of modified PVA was confirmed by FTIR and 1H NMR spectra and further it was characterized by TGA, DSC, and SEM. The tensile strength and % elongation for the structurally modified PVA were determined. The FTIR spectrum showed peaks corresponding to the CO and CS stretching due to the grafted drug molecules. The 1H NMR spectrum showed the acrylic CH2 proton signal of PVA around 1.6 ppm. The SEM showed different surface morphology for the structurally modified PVA. The mechanical properties of the structurally modified PVA was found to be reduced due to the presence of traces of solvent molecules and the breaking of inter‐ and intramolecular hydrogen bonding. The sustainable drug release through hydrolysis mechanism was tested at the pH of 7.3. Generally, the drug release followed the Korsmeyer–Peppas model with Fickian drug transportation mechanism except Furosemide (Fur)‐grafted PVA system at the pH of 7.3. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46620.

Intramolecular O-H⋯O and C-H⋯O hydrogen bond cooperativity in D-glucopyranose and D-galactopyranose-A DFT/GIAO, QTAIM/IQA, and NCI approach.

Density functional theory calculations are used to compute proton nuclear magnetic resonance (NMR) chemical shifts, interatomic distances, atom-atom interaction energies, and atomic charges for partial structures and conformers of α-D-glucopyranose, β-D-glucopyranose, and α-D-galactopyranose built up by introducing OH groups into 2-methyltetrahydropyran stepwisely. For the counterclockwise conformers, the most marked effects on the NMR shift and the charge on the OH1 proton are produced by OH2, those of OH3 and OH4 being somewhat smaller. This argues for a diminishing cooperative effect. The effect of OH6 depends on the configuration of the hydroxymethyl group and the position, axial or equatorial, of OH4, which controls hydrogen bonding in the 1,3-diol motif. Variations in the interaction energies reveal that a "new" hydrogen bond is sometimes formed at the expense of a preexisting one, probably due to geometrical constraints. Whereas previous work showed that complexing a conformer with pyridine affects only the nearest neighbour, successive OH groups increase the interaction energy of the N⋯H1 hydrogen bond and reduce its length. Analogous results are obtained for the clockwise conformers. The interaction energies for C-H⋯OH hydrogen bonding between axial CH protons and OH groups in certain conformers are much smaller than for O-H⋯OH bonds but they are largely covalent, whereas those of the latter are predominantly coulombic. These interactions are modified by complexation with pyridine in the same way as O-H⋯OH interactions: the computed NMR shifts of the CH protons increase, the atom-atom distances are shorter, and interaction energies are enhanced.

Selective Single-Site Pd-In Hydrogenation Catalyst for Production of Enhanced Magnetic Resonance Signals using Parahydrogen.

Pd-In/Al2 O3 single-site catalyst was able to show high selectivity (up to 98 %) in the gas phase semihydrogenation of propyne. Formation of intermetallic Pd-In compound was studied by XPS during reduction of the catalyst. FTIR-CO spectroscopy confirmed single-site nature of the intermetallic Pd-In phase reduced at high temperature. Utilization of Pd-In/Al2 O3 in semihydrogenation of propyne with parahydrogen allowed to produce ≈3400-fold NMR signal enhancement for reaction product propene (polarization=9.3 %), demonstrating the large contribution of pairwise hydrogen addition route. Significant signal enhancement as well as the high catalytic activity of the Pd-In catalyst allowed to acquire 1 H MR images of flowing hyperpolarized propene gas selectively for protons in CH, CH2 and CH3 groups. This observation is unique and can be easily transferred to the development of a useful MRI technique for an in situ investigation of selective semihydrogenation in catalytic reactors.

Does the Intramolecular Hydrogen Bond Affect the Spectroscopic Properties of Bicyclic Diazole Heterocycles?

The formation of an intramolecular hydrogen bond in pyrrolo[1,2-a]pyrazin-1(2H)-one bicyclic diazoles was analyzed, and the influence of N-substitution on HB formation is discussed in this study. B3LYP/aug-cc-pVDZ calculations were performed for the diazole, and the quantum theory of atoms in molecules (QTAIM) approach as well as the natural bond orbital (NBO) method was applied to analyze the strength of this interaction. It was found that the intramolecular hydrogen bond that closes an extra ring between the C=O proton acceptor group and the CH proton donor, that is, C=O⋯H–C, influences the spectroscopic properties of pyrrolopyrazine bicyclic diazoles, particularly the carbonyl frequencies. The influence of N-substitution on the aromaticity of heterocyclic rings is also discussed in this report.

Microhydration of PAH+ cations: evolution of hydration network in naphthalene+-(H2O) n clusters (n ≤ 5).

The interaction of polycyclic aromatic hydrocarbon molecules with water (H2O = W) is of fundamental importance in chemistry and biology. Herein, size-selected microhydrated naphthalene cation nanoclusters, Np+-W n (n ≤ 5), are characterized by infrared photodissociation (IRPD) spectroscopy in the C-H and O-H stretch range to follow the stepwise evolution of the hydration network around this prototypical PAH+ cation. The IRPD spectra are highly sensitive to the hydration structure and are analyzed by dispersion-corrected density functional theory calculations (B3LYP-D3/aug-cc-pVTZ) to determine the predominant structural isomers. For n = 1, W forms a bifurcated CH···O ionic hydrogen bond (H-bond) to two acidic CH protons of the bicyclic ring. For n ≥ 2, the formation of H-bonded solvent networks dominates over interior ion solvation, because of strong cooperativity in the former case. For n ≥ 3, cyclic W n solvent structures are attached to the CH protons of Np+. However, while for n = 3 the W3 ring binds in the CH···O plane to Np+, for n ≥ 4 the cyclic W n clusters are additionally stabilized by stacking interactions, leading to sandwich-type configurations. No intracluster proton transfer from Np+ to the W n solvent is observed in the studied size range (n ≤ 5), because of the high proton affinity of the naphthyl radical compared to W n . This is different from microhydrated benzene+ clusters, (Bz-W n )+, for which proton transfer is energetically favorable for n ≥ 4 due to the much lower proton affinity of the phenyl radical. Hence, because of the presence of polycyclic rings, the interaction of PAH+ cations with W is qualitatively different from that of monocyclic Bz+ with respect to interaction strength, structure of the hydration shell, and chemical reactivity. These differences are rationalized and quantified by quantum chemical analysis using the natural bond orbital (NBO) and noncovalent interaction (NCI) approaches.

New organoselenium compounds with intramolecular Se⋯O/ Se⋯H interactions: NMR and theoretical studies

New 1,3-bis(phenylselanylmethyl)benzene (1, 2 and 4) and butyl phenylselane derivatives (3 and 5) are synthesized and full heteronuclear NMR characterization of these compounds are reported. Interestingly, NMR spectrum of compounds 2–5 show coupling of 1H and 13C signals of groups involved in intramolecular nonbonding interactions with 77Se. The coupling constants JH-Se and JC-Se are in the range 13.6–21.6 Hz and 28–49 Hz, respectively. For compounds 4 and 5, JH-Se coupling constants of formyl proton are smaller than their respective acetal CH protons for compounds 2 and 3. However, this trend is opposite for JC-Se coupling constants, indicating that in formyl group containing compounds 4 and 5, Se⋯O interactions are present while in compounds 2 and 3 with acetal fragments, Se⋯H interactions also could be present because of steric constraints. To confirm these interactions, quantum chemical analyses were performed for 2, 4 and 5. The minimal energy conformation for these compounds present Se⋯O/Se⋯H interactions and are at lower energy in comparison to different conformers which do not show any interaction. For compounds 4 and 5, minimal energy conformation present Se⋯O interactions and for compound 2, Se⋯H is the favored conformation. These results are in accordance with the NMR data for these compounds. X-ray crystal structure of compound 1,3-bis(phenylselanylmethyl)benzene (1) was also determined during this work. In order to understand the effect of the Se⋯O/Se⋯H interactions and the position of phenylselanylmethyl groups, quantum chemical analyses were also carried out for 1,4-bis(phenylselanylmethyl)benzene derivatives (6 and 7). Interestingly, minimal energy conformers of 1,3-bis(phenylselanylmethyl)benzene derivatives 2 and 4 are more stable than their corresponding conformers of 1,4-bis-(phenylselanylmethyl)benzene derivatives 6 and 7.1,3-bis[{(2-(diethoxymethyl)phenyl)selanyl}methyl]benzene (2) with an energy barrier of 16.22 kcal/mol is more stable than corresponding 1,4-bis [{(2-(diethoxymethyl)phenyl)selanyl}methyl]benzene (7), while molecule 4 is 1.79 kcal/mol more stable than its corresponding 2'-[{1,4-phenylenebis(methylene)}bis(selanediyl)]dibenzaldehyde (6).

Infrared Spectroscopic Study of the Acidic CH Bonds in Hydrated Clusters of Cationic Pentane.

Infrared spectroscopy of the hydrated clusters of cationic pentane, which are generated through the vacuum ultraviolet photoionization in the gas phase, is carried out to probe the acidic properties of their CH bonds. The monohydrated pentane cation forms the proton-shared structure, in which the proton of CH in cationic pentane is shared between the pentyl radical and water molecule. In the di- and trihydrated clusters, the proton of CH is completely transferred to the water moiety so that the clusters are composed of the pentyl radical and protonated water cluster. These results indicate that two water molecules are enough to cause the proton transfer from CH of cationic pentane, and thus its acidity is highly enhanced with the ionization.

Generation of ferrocenylvinyl cation CpFeC5H4–C+=CH2 by protonation of ferrocenylacetylene with Nafion and its reactions with SMe2 and PPh3 in scCO2 giving onium salts

Cation CpFeC5H4–C+=CH2 was obtained by protonation of FcC CH with Nafion superacid in DMF or scCO2 and characterized by NMR spectroscopy. The protonation in the presence of SMe2 or PPh3 affords new onium derivatives, which were isolated as the tetrafluoroborate salts.

2JHH-resolved HSQC: Exclusive determination of geminal proton-proton coupling constants

The measurement of two-bond proton-proton coupling constants (2JHH) in prochiral CH2 groups from the F2 dimension of 2D spectra is not easy due to the usual presence of complex multiplet J patterns, line broadening effects and strong coupling artifacts. These drawbacks are particularly pronounced and frequent in AB spin systems, as those normally exhibited by the pair of diastereotopic CH2 protons. Here, a novel 2JHH-resolved HSQC experiment for the exclusive and accurate determination of the magnitude of 2JHH from the doublet displayed along the highly-resolved indirect F1 dimension is described. A pragmatic 2JHH NMR profile affords a fast overview of the full range of existing 2JHH values. In addition, a 2JHH/δ(13C)-scaled version proves to be an efficient solution when severe signal overlapping complicate a rigorous analysis. The performance of the method is compared with other current techniques and illustrated by the determination of challenging residual dipolar 2DHH coupling constants of small molecules dissolved in weakly orienting media.

Bis(alkyl)thioethers on a biphenyl scaffold: A spectroscopic and structural insight

A series of bis(alkyl)thioether compounds utilising biphenyl as the backbone of the type 2,2′-bis(alkylthio)-1,1′-biphenyl have been prepared with yields of 32–70%. The six benzyl derivatives all displayed an AB quartet for the CH2 hydrogens within their 1H NMR spectra due to restricted rotation within the molecule. Where the alkyl group was changed to neopentyl the CH2 protons became equivalent giving rise to a singlet within the 1H NMR spectrum. The compounds have been characterised principally using multinuclear NMR spectroscopy and single crystal X-ray diffraction.

Structural discrimination from in situ measurement of 1DCH and 2DHH residual dipolar coupling constants

A fast residual dipolar coupling constant-assisted strategy involving the simultaneous determination of scalar and total coupling constants from a single 1 JCH /2 JHH -resolved NMR spectrum is reported. It is shown that the concerted use of the directly measured 1 DCH (for all CHn multiplicities) and 2 DHH residual dipolar couplings allows an on-the-fly assignment of diastereotopic CH2 protons, as well as of an efficient discrimination between diastereoisomeric structures of strychnine which contains six stereocenters. Copyright © 2017 John Wiley & Sons, Ltd.

Modification of Porang (<em>Amorphophallus oncophyllus</em>) Flour by Acid and Thermal Process using Conventional Heating in Waterbath and Microwave Irradiation

Modified porang flour by lactic acid and conventional heating using waterbath (PAW) and microwave radiation (PAM) were determined its functional group using FTIR, the chemical structure were studied using H1NMR, molecular weight were measured using HPLC-SEC and its microstructure were studied using SEM, particles size were measured using PSA and rheology characteristics were determined using Rheometer. The results showed that modified porang either PAW and PAM showed changes on functional group peaks compared to one of native porang flour included OH, CH₃, C-C, C = O, C-O-C, mannose and glucose groups. H¹NMR spectra of modified porang flour (PAW and PAM) were similar mainly in proton of CH₃ and CH₂, molecular weight were higher at PAW 2.0×10⁶ and PAM 3.0×10⁶, while particles size of PAW and PAM were smaller. The microstructure of PAW and PAM were porous and spongy indicated that PAW and PAM had higher moisture accessability on the amorph site. Storage modulus (G’) dan loss modulus (G”) PAW and PAM decreasing with the increased temperature. Lower G’ compared to G” and modulus (G’ and G”) did not showed crossing indicated that PAW and PAM have a stable visco-elasticity. It can be concluded that functional group peaks of modified porang flour (PAW and PAM) changed differently compared to native porang flour, H¹ -NMR spectra of modified porang flour were similar, with bigger moleculer weight of PAM than PAW, the microstructure were porous and spongy and rheology characteristics indicated that an unchanged visco-elastic system by thermal treatments.

Synthesis, growth, optical and DFT calculation of 2-naphthol derived Mannich base organic non linear optical single crystal for frequency conversion applications

2-naphthol derived Mannich base 1-((4-methylpiperazin-1-yl) (phenyl) methyl) naphthalen-2-ol (MPN) – a nonlinear optical single crystal was synthesized and successfully grown by slow evaporation technique at room temperature. The molecular structure was confirmed by single crystal XRD, FT-IR, 1H NMR and 13C NMR spectral studies. The single crystal X-ray diffraction analysis reveals that the crystal belongs to orthorhombic crystal system with non-centrosymmetric space group Pna21. The chemical shift of 5.34ppm (singlet methine CH proton) in 1H NMR and signal for the CH carbon around δ70.169ppm in 13C NMR confirms the formation of the title compound. The crystal growth pattern and dislocations of crystal are analyzed using chemical etching technique. UV cut off wavelength of the material was found to be 212nm. The second harmonic generation (SHG) of MPN was determined from Kurtz Perry powder technique and the efficiency is almost equal to that of standard KDP crystal. The laser damage threshold was measured by passing Nd: YAG laser beam through the sample and it was found to be 1.1974GW/cm2. The material was thermally stable up to 142°C. The relationship between the molecular structure and the optical properties was also studied from quantum chemical calculations using Density Functional Theory (DFT) and reported for the first time.

Association of symmetrical alkane diols with pyridine: DFT/GIAO calculation of 1H NMR chemical shifts

Proton nuclear magnetic resonance (NMR) shifts of the free diol and of its 1 : 1 and 1 : 2 hydrogen-bonded complexes with pyridine have been computed for five symmetrical alkane diols on the basis of density functional theory, by applying the gauge-including atomic orbital method to geometry-optimized conformers. For certain conformers, intramolecular OH···OH interactions, evidenced by high NMR OH proton shifts, are further enhanced on going from the free diol to the corresponding 1 : 1 diol/pyridine complex. This is confirmed by atoms-in-molecules and non-covalent interaction plots. The computed OH and CH proton shifts for the diol and the two complexes correlate well with values obtained by analysing data from the NMR titration of the diols in benzene against pyridine. Shift values for the diols in neat pyridine are calculated by weighting the shifts of the various protons in the three forms (free diol, 1 : 1 and 1 : 2 diol/pyridine complexes) according to the experimentally determined association constants. The results are in good agreement with those observed, and after empirical scaling, the root mean square difference is 0.18 ppm. Copyright © 2016 John Wiley & Sons, Ltd.