Ab initio MO calculations and 17O NMR at natural abundance of para-substituted acetophenones

¹⁷O NMR chemical shifts and calculated (ab initio MO theory) electron densities are reported for a series of para-substituted acetophenones, X? C₄H₆? COCH₃, where X = NH₂, OCH₃, F, Cl, CH₃, H, COCH₃, CN, NO₂. The ¹⁷O shifts are very sensitive to the para substituent and cover a range of some 51 ppm. Donors induce upfield shifts and acceptors downfield shifts. The substituent chemical shifts (SCS) correlate precisely with σ_I and σ_R⁺ using the Dual Substituent Parameter (DSP) method. The derived transmission coefficients ρ_I and ρ_R indicate that polar and resonance mechanisms contribute approximately equally to the observed substituent effects. The shifts also correlate well with calculated π-electron densities (slope = 1500 ppm per electron) confirming their electronic origin. λ values are also reported, and the role of the average excitation energy, ΔE, in determining ¹⁷O SCS values is discussed. It is concluded that variations in ΔE are minor and that the local Δ-electron density is the dominant feature controlling ¹⁷O SCS values.     

Carbon‐13 NMR and PM3 Study on the Substituent Effect of 1‐Aryl‐3,3‐Difluoro‐2‐Halocyclopropenes

The substituent‐induced chemical shifts (SCS) of C2 and C3 on the ¹³C NMR spectra of 1‐aryl‐3,3‐difluoro‐2‐halocyclopropenes were studied. The correlation between SCS and Hammett constants shows that the tendency of effect by the substituents on the phenyl ring is BrC2(ρ = 4.66) > ClC2(ρ = 4.50) and ClC3(ρ = ?1.63) > BrC3(ρ = ?1.41). The DSP treatment further confirms the SCS of C2 and C3 are the main contribution of the resonance effect and field effect, respectively. Those results of the incremental shifts reveals that the gem‐difluorocyclopropenyl bearing the phenyl group possesses a triple bond character, which is also observed in IR spectra with high n?_C=C (1768–1945 cm^?1).     

1H-NMR Spectroscopy of Gold Drugs. High-Resolution Studies of β-D-Thioglucosetetraacetate Phosphine Complexes of Au(I)

¹H-NMR data (11.74 Tesla) for the gold(I) complexes [R₃P-Au-(2,3,4, 6-tetra-O-acetyl-1-thio-β-D -glucopyranosido-S)] (R = Et, Cyclohexyl, C₆H₅, p-CH₃OC₆H₄) with sulfur coordination to gold, are reported. The resonances associated with the sugar protons have been assigned although these have similar chemical environments. The coordination chemical shifts, Δδ, for the Au? S? C? H proton are ≈? 0.6 ppm, and support S-coordination to gold.     

13C n.m.r. studies of organosilanes: II—substituent chemical shift parameters for alkoxysilanes

The ¹³C n.m.r. spectra of forty alkoxysilanes of the general type X_nSi(OR)_4–n (X = CH₃, C₆H₅, H; R = CH₃, C₂H₅, n-C₃H₇, i-C₃H₇, n-C₄H₉, i-C₄H₉, s-C₄H₉, n-C₅H₁₁, CH(CH₃)(C₆H₅), C₆H₅) have been recorded and assigned. The chemical shifts of the α-carbon resonances of the alkoxy groups are shown to depend on both the nature of the alkoxy group and the number and type of substituents on the silicon. Regression analyses of the data give empirical substituent chemical shift (SCS) parameters for the silyl substituents. The β-carbon resonances are shown to be dependent on the presence of the silyl group, but not the specific silyl substituents.     

Applications of 95Mo NMR. 5—substituent effects in the 95Mo and 13C NMR spectra of benzyltricarbonyl(η5-cyclopentadienyl)molybdenum(II) derivatives

A systematic study has been made of the effects of substituent induced chemical shifts in [(η⁵-C₅H₅)(CO)₃Mo(CH₂C₆H₄R)] compounds. Both ⁹⁵Mo and ¹³C NMR shifts in the aromatic ring are reported. The (η⁵-C₅H₅)(CO)₃MoCH₂? group is a reasonably strong resonance donor (σ_R° = ?0.21) and weak inductive donor (σ_I = ?0.07). The molybdenum chemical shifts are extremely sensitive to the effects of distant substituents (range c. 40 ppm). Since the shift correlates well with substituent constants in this series, it is suggested that the chemical shift is controlled by the paramagnetic term for this spin 5/2 nucleus.     

Studies on main group metal-transition-metal bonded compounds 7. A 199Hg NMR study of home group of some group VI trasition-metal mercury compounds

A ¹⁹⁹Hg Fourier Tranformation NMR study has been carried out on Hg[M(CO)₃C₅H₅]₂ (M = Cr, Mo, W), [C₅H₅(CO)₃M]HgCl, and [C₅H₅(CO)₃W]HgX (X = Cl, Br, I, SCN). The ¹⁹⁹Hg chemical shifts are ?80, +115 and ?348 ppm respectively for the symmetrical compounds, ?542, ?617, and ?997 ppm for the chloride and ?1200, ?1529 and ?924 ppm for the Br, I, SCN-tungsten derivatives respectively. The ₁₉₉Hg chemical shifts for several other mercury derivatives are reported for comparison. All chemical shifts are relative to 90% HgMe₂/10% internal lock C₆F₆ with positive values indicating decreasing shielding. The J_199Hg-183W values are 151, 706, 690, 630 and 684 Hz for the symmetrical compound and the Cl, Br, I and SCN derivatives respectively. The factors which may influence these parameters are discussed briefley.     

Carbon-13 NMR studies of quinolines and isoquinolines. II. Chlorine–nitrogen interactions and N-oxide effects

Carbon-13 chemical shift assignments are reported for four chloroquinolines, six chloroisoquinolines, one dichloroquinoline, four dichloroisoquinolines, four methylchloroquinolines, two methylchloroisoquinolines, quinoline N-oxide, isoquinoline N-oxide, five methylquinoline N-oxides, two methylisoquinoline N-oxides and three chloroisoquinoline N-oxides. Chlorine substituent chemical shift (SCS) effects are reported for the alpha, ortho, meta, para and peri positions. Consistent patterns are observed for the para and peri positions, a vinylogous ortho pattern is reported and the additivity of these SCS effects is demonstrated. Alpha SCS effects vary widely from 1.1 ppm upfield in 1-chloroisoquinoline to 6.7 ppm downfield in 4-chloroquinoline. These results, together with those in the literature, permit the definition of steric and nitrogen lone-pair contributions which modify the ‘normal’ chlorine SCS effect, and these modifying contributions are shown to be roughly additive. Large (6–16 ppm) upfield shifts are observed for the carbons ortho and para to the N-oxide group. The individual magnitudes of these shifts and their sum are constant and the effects are additive in substituted systems. A 9.5 ppm upfield shift is also observed for C-8 in quinoline N-oxides which is attributed to a space–charge interaction. Substituent chemical shift (SCS) effects for the chloro and methyl groups and the chemical shifts of the methyl carbons are essentially the same in the N-oxides as in the parent heterocycles and are additive, except for those molecules where the substituent is adjacent to the N-oxide moiety, in which cases substantial interactions are observed.     

15N NMR spectroscopy of 3‐substituted 5‐trichloromethyl‐1,2‐dimethyl‐1H‐pyrazolium chlorides

¹⁵N NMR data of a series of 3‐alkyl[aryl] substituted 5‐trichloromethyl‐1,2‐dimethyl‐1H‐pyrazolium chlorides (where the 3‐substituents are H, Me, Et, n‐Pr, n‐Bu, n‐Pe, n‐Hex, (CH₂)₅CO₂Et, CH₂Br, Ph and 4‐Br‐C₆H₄), are reported. The ¹⁵N substituent chemical shifts (SCS) parameters are determined and these data are compared with the ¹³C SCS values and data obtained by MO calculations. Copyright © 2002 John Wiley & Sons, Ltd.     

The NMR spectra of porphyrins—12: 13C and proton NMR spectra of the zinc(ii)coproporphyrin isomers2

The ¹³C and proton NMR spectra of the zinc(II) complexes of the tetramethyl esters of the four coproporphyrin type isomers are reported and assigned. Effects of aggregation phenomena on these shifts are discussed and a method involving addition of a slight excess of pyrrolidine is proposed for measurement of the spectra of the “monomeric” species; spectra obtained under these conditions are capable of simple, straight-forward interpretation and assignment in terms of molecular symmetry. Thus, a facile distinction between the type isomers is obtained.The “monomer” chemical shifts so derived allow consistent SCS parameters to be derived. The C_β-Me SCS are shown to be related to the bond order of the C_β-C_β bond in the porphyrin ring, and are thus quite different from the corresponding SCS in pyrroles.Aggregation shifts in the ¹³C and proton spectra are shown to be consistent with the presence of “stacked” aggregates with the ring current of one molecule affecting the other, together with an additional effect on the chemical shifts of the meso carbons, which is probably steric in origin.     

Nucleophilic Substitutions of N-Acyl-4-Chloro-3-Thiazolidines with the Organometallic Selenolates LiSeMcp(CO)3, M = Mo,W. Crystal Structure of (RS)-3-Acetyl-4-[(η5-cyclopentadienyl)(tricarbonyl)selenolato-tungsten(II)]-2,2,5,5-tetramethyl-3-thiazolidine

Selenolato complexes of molybdenum(II) and tungsten(II) with biologically important thiazolidine N/S-heterocycles have been prepared via nucleophilic attack of LiSeMocp(CO)₃ or LiSeWcp(CO)₃ on N-acyl-4-chloro-thiazolidines, easily accessible by reaction of acyl chlorides with 3-thiazolines. The resulting complexes represent the first examples of organometallic derivatives of this class of heterocycles. They are stable under nitrogen in the solid state, but decompose in solution when exposed to air. An X-ray structure analysis of (RS)-3-acetyl-4-[(η⁵-cyclopentadienyl)(tricarbonyl)(selenolato)tungsten(II)]-2,2,5,5-tetramethyl-3-thiazolidine ( 2 a ) has been performed (C₁₇H₂₁NO₄SSeW, orthorhombic, Pbca, a = 1579.5(3) pm, b = 1138.7(2) pm, c = 2209.4(3) pm, Z = 8). It revealed a monomeric structure with a non-planar heterocyclic substituent in an envelope conformation and a W–Se bond length of 264.96(10) pm. ⁷⁷Se-NMR spectra displayed chemical shifts in the range –280 to –350 ppm. These values are consistent with earlier results on related complexes.     

The NMR spectra of porphyrins—19: 13C and proton NMR spectra of metal-free porphyrins with the Type-IX substituent orientation,and of their zinc(II) complexes

The ¹³C and proton NMR spectra of six porphyrins bearing the substituent orientation characteristic of the natural “Type-IX” arrangement are reported and assigned. Significant concentration effects in the spectra of the free base porphyrins, together with the broadening of the C_α (and occasionally C_β) carbon resonances due to NH tautomerism caused a significant loss of data in these spectra. However, the spectra of the corresponding zinc(II) porphyrins (with addition of excess pyrrolidine) show that both these extraneous effects are completely removed to give well-resolved spectra with accurately reproducible chemical shifts. These spectra are assigned and an analysis of the chemical shifts allows the deduction of substituent chemical shift (SCS) parameters for the peripheral substituents at the beta and meso carbons. There is no global effect of these beta substituents, the beta carbon SCS being confined to the immediate pyrrole ring, and the meso carbon SCS to the two adjacent pyrrole rings. The SCS parameters are analyzed and it is shown how they can be used to predict the peripheral and meso carbon chemical shifts of any porphyrin bearing the substituents discussed.     

SUBSTITUENT CHEMICAL SHIFT (SCS) AND THE SEQUENCE STRUCTURE OF ETHYLENE-VINYL ALCOHOL COPOLYMERS

Three ethylene-vinyl alcohol copolymers were studied by means of the substituent chemical shift (SCS) method. The SCS parameters of hydroxy (-OH) in two different solvents were obtained: in deuterium oxide/phenol (20/80 W/W ) the parameters are S_1 = 42.77±0.08ppm, S_2 = 7.15±0.06 ppm, S_3 (s)= -4.08±0.02ppm, S_3 (t) =-3.09±0.20ppm,S_4 = 0.48±0.03ppm, S_5 = 0.26±0.05ppm. In o-dichloro-benzen-d_4 S_1(s)=44.79±0.61ppm, S_2=7.40±0.00ppm, S_3(s)=-4.51±0.17ppm, S_3(t)=-3.13 ±0.00 ppm, S_4 =0.63±0.04ppm, S_5=0.36±0.00ppm.Simultaneously the ~(13)CNMR spectra of EVA copolymers were assigned by using the SCS parameters obtained.     

Fluoroazoles. III. Synthesis and 1H and 1–9F nmr spectra of 3-, 4-, and 5-fluoro-1-methylpyrazole

The three monofluoro derivatives of N-methylpyrazole have been synthesized. 3-Fluoro-1-methylpyrazole and 4-fIuoro-1-methylpyrazole were prepared from the appropriate amines by diazotization and photochemical irradiation of the diazonium salts in tetrafluoroboric acid. 5-Fluoro-1-methylpyrazole was obtained from 1-acetyl-3-fluoropyrazole and methyl fluorosulfonate, and also by direct methylation of 3(5) fluoropyrazole with dimethyl sulfate. The ^1–9F chemical shifts of these N-methylated fluoroazoles cover a great range (ca. 50 ppm) and show a good correlation with the chemical shifts of H₃, H₄, and H₅ protons of 1-methylpyrazole. An unexpected long-range coupling ⁵J (F-CH₃) is observed in 3-fluoro-1-methylpyrazole.     

Carbon-13 NMR spectra of a series of para-substituted N,N-dimethylbenzamides. Comparisons of linear free energy relationships for carbon-13 and nitrogen-15 chemical shifts and rotation barriers

All carbon-13 chemical shifts for 11 para-substituted N,N-dimethylbenzamides in 1 mole % chloroform solution are reported, with assignments based upon double resonance experiments, analogy to chemical shifts of benzamide, and self-consistency between experimental and calculated values using recognized substituent parameters. In contrast to earlier reports, the aryl carbon chemical shift assignments for N,N-dimethylbenzamide are C-2, 127.0; C-3, 128.7; C-4, 129.4, and for p-chloro-N,N-dimethylbenzamide are C-1, 134.6; C-4, 135.5 ppm, relative to internal TMS. Good Hammett correlations (σ_p) are reported for ¹³C chemical shifts of C-1 (σ = 11.9 ppm) and even for the carbonyl group (σ = ?2.3 ppm) but are markedly improved if correlated with σ_p+ (σ = 9.5 ppm) and Dewar's F (σ = ?1.9 ppm), respectively. Excellent Swain–Lupton F and R correlations were found for some of the ¹³C chemical shifts and yielded values for percent resonance contributions to transmission of substituent effects as follows, C-1, 75 ± 4%; C-2, 51 ± 3%; C?O, 31±2%. These are compared to similar values calculated from the C?O of benzoic acids of 34±10%, and from the nitrogen-15 chemical shifts of benzamides of 56±2%. Correlations of these ¹³C δ values and ¹⁵N δ values with rotation barriers (ΔG) for N,N-dimethylbenzamides were examined, and it was found that while C?O δ values correlated only poorly the C-1 δ values correlated very well, but the best correlation was for ¹⁵N δ values of benzamides. It is suggested that Δ G and δ ¹⁵N are intrinsically related due to their numerical correlation, and the close similarity in percent resonance contribution of substituent influence on these parameters.     

1H NMR spectra part 31: 1H chemical shifts of amides in DMSO solvent

The ¹H chemical shifts of 48 amides in DMSO solvent are assigned and presented. The solvent shifts Δδ (DMSO‐CDCl₃) are large (1–2 ppm) for the NH protons but smaller and negative (?0.1 to ?0.2 ppm) for close range protons. A selection of the observed solvent shifts is compared with calculated shifts from the present model and from GIAO calculations. Those for the NH protons agree with both calculations, but other solvent shifts such as Δδ(CHO) are not well reproduced by the GIAO calculations. The ¹H chemical shifts of the amides in DMSO were analysed using a functional approach for near ( ≤ 3 bonds removed) protons and the electric field, magnetic anisotropy and steric effect of the amide group for more distant protons. The chemical shifts of the NH protons of acetanilide and benzamide vary linearly with the π density on the αN and βC atoms, respectively. The C=O anisotropy and steric effect are in general little changed from the values in CDCl₃. The effects of substituents F, Cl, Me on the NH proton shifts are reproduced. The electric field coefficient for the protons in DMSO is 90% of that in CDCl₃. There is no steric effect of the C=O oxygen on the NH proton in an NH…O=C hydrogen bond. The observed deshielding is due to the electric field effect. The calculated chemical shifts agree well with the observed shifts (RMS error of 0.106 ppm for the data set of 257 entries). Copyright © 2014 John Wiley & Sons, Ltd.     

Theoretical study on electronic structures and spectroscopic regularities of ethylated single-walled carbon nanotubes

The electronic structures of a series of ethylated single-walled carbon nanotubes (SWCNTs) were studied using density; function theory (DFT) at B3LYP/6-31G(d) level. The bond vertical to the main axis of the SWCNT was predicted to be the most thermodynamically stable additive site by ethylene. The energy gaps of the ethylated SWCNTs decrease with the decrease in the symmetries after the addition. The C-C and C=C stretching vibrations in the IR spectra of the ethylated SWCNTs, compared with those in the IR spectra of the pristine SWCNTs, are red-shifted. The chemical shifts at 172.9 ppm of the bridged carbon atoms in the NMR spectrum of (3,3)-C₂H₄(v) (C₃₆C₂H₄) are shifted downfield in comparison with those at 144.7 ppm of the same carbon atoms in (3,3) (C₃₆). Meanwhile, (3,3)-C₂H₄(v) (C₃₆C₂H₄) shows a weakened anti-aromaticity owing to a nuclear independent chemical shift (NICS) at 3.6 ppm, relative to the NICS value at 6.3 ppm of (3,3) (C₃₆).     

Topology and Equilibrium Analysis of the Monovalent Aluminum Compound Al4Cp*Ph4

The theoretical structure and thermochemistry of the tetrameric, low‐valence aluminum compound Al₄Cp*^Ph₄ (Cp*^Ph = C₅Me₄Ph) is discussed. The first synthesis of this compound was reported in 2005, but the compound failed to crystallize and experimental ²⁷Al NMR results were inconclusive in regard to the degree of association. Here density functional theory combined with a genetic algorithm is used to predict the expected structure and properties for Al₄Cp*^Ph₄. Synthesis efforts were repeated for this compound, resulting in a product with a ²⁷Al NMR chemical shift that differed from the previous report by nearly 20 ppm. However, calculated ²⁷Al NMR chemical shifts for the theoretically predicted structure are within one ppm of these new experimental results, strongly suggesting the tetrameric form has been synthesized. Previous work on five Al₄R₄ (R = C₅H₅, C₅Me₄H, C₅Me₅, C₅Me₄iPr, C₅Me₄Pr) compounds showed a general trend towards an increased likelihood of disassociation into monomeric species in solution as ligand bulk increased. Analysis of Al₄Cp*^Ph₄, the sixth and bulkiest compound in this series, indicates a departure from this trend. Bonding characteristics for monomer and tetramer forms in this series are examined in detail via topological analysis to understand this trend.     

Solvent-Induced Deuterium Isotope Effects in 13C- and 15N-NMR. Spectra of Enaminones

The effect of deuterium on the ¹³C and ¹⁵N chemical shifts of enaminones has been investigated. D/H isotope shifts are reported for neutral and protonated species, i.e., when the isotope is exchanged on the C(2)-, N-, or O-atoms. In cases of slow exchange the isotope shifts were obtained from solutions containing both isotopomers, whereas for fast exchange (acidic solutions) either separate NMR. sample tubes (¹⁵N-NMR.) or coaxial tubes (¹³C-NMR.) were used. In neutral molecules the isotope effects δ_C(D, H) are intrinsic in nature. In acidic solutions, the enaminocarbonyl cations formed exhibit δ_C(D, H)- and δ_N(D, H)-values which are discussed in terms of the proton transfer. The mesomeric character of the cations is reflected by characteristic features in the δ_C(D, H)- and δ_N(D, H)-values, which can be ascribed to isotopic perturbation of resonance. O-Protonation shifts in the ¹⁵N-resonance, observed for the first time, are large and positive (+60 to +76 ppm), in contrast to amides, where the effects are of the same sign but an order of magnitude smaller. Both protonation shifts and solvent-induced isotope effects are discussed in connection with the nucleophilic character of the reactive centers in the enaminone synthon.     

A13C nuclear magnetic resonance study of some linear alkynyl gold(I) and silver(I) complexes

Summary Phenylacetylide gold(I) and silver(I) compounds of the type [n-Bu₄N][M(C=CPh)₂], (1) and [n-Bu₄N][XMC=CPh], (2) have been studied by¹³C n.m.r. spectroscopy and their chemical shifts are reported for the first time. The shielding of the alkynyl carbon linked directly to the metal in (2) isca. 10–15 ppm less than the analogous carbon in (1) (M=Au), andca. 6–11 ppm less in the silver complexes (M=Ag). The variation in chemical shift depends on the nature of X(X=Cl, Br, I, C₂Ph and Ph₃P) and indicates greatly different degrees of polarization of the Au-C= (or Ag-C=) bonds in (1) and (2). I.r. spectra of the title compounds are reported and confirm the weakness of ML back-bonding. Comparison is also made with¹³C and i.r. data for platinum, and mercury complexes.     

17O NMR spectroscopy: Effect of substituents on chemical shifts for p-substituted benzoic acids,methyl benzoates,cinnamic acids and methyl cinnamates

The ¹⁷O NMR spectra for a series of ¹⁷O-enriched p-substituted benzoic acids, methyl benzoates, cinnamic acids and methyl cinnamates in acetone at 40°C are reported. The carboxylic acids showed one signal (benzoic 250.5 ppm, SCS range p-MeO to p-NO₂ = 10.5 ppm; cinnamic 254.1 ppm, SCS range p-MeO to p-NO₂ = 5.4 ppm). The esters showed two signals [methyl benzoate (C?O) 341.3 ppm and (OCH₃) 128.0 ppm; methyl cinnamate (C?O) 339.9 ppm and (OCH₃) 134.2 ppm]. The SCS ranges for the carbonyls of the esters were larger than those for the corresponding acids, while those for the OCH₃ groups of the esters were slightly smaller. The carbonyl data gave good correlations with σ⁺ constants, while the OCH₃ data gave at best only a poor correlation with σ constants. Dual substituent parameter treatment improved the correlations for all the data using σ_R+ constants. The ratios of ρ_I to ρ_R+ were similar for all the sets of data.