Effects of some phosphorus substituents on the carbon-13 chemical shifts of alkyl chains

The carbon-13 NMR spectra of 16 aliphatic phosphorus compounds with -PCl₂, -P(OCH₃)₂, -P(CH₃)₂ or -PS(CH₃)₂ groups were determined and interpreted on the basis of the usual α, β-deshielding and γ-shielding effects. The α-effects of all the groups were quite large (15 to 30 ppm), though the β-effects were small (0 to 3 ppm). The γ-effects were also small (0·2 to 1·6 ppm), but of significance in suggesting reduced steric compression relative to that found for methyl and most of the common organic functional groups. This may be attributed to the greater length of the C? P bond. The phosphorus-31 NMR spectra of these compounds also show the existence of interaction with γ-carbons by exhibiting small additive upfield shifts.     

Downfield γ-gauche and γ-antiperiplanar effects on 13C NMR chemical shifts exerted by thiophene sulphur

The γ-effects of sulphur on ¹³C NMR chemical shifts have been measured in a series of steroidal compounds containing the thiophene ring in different configurations with respect to the rest of the molecule. The data constitute the first example of downfield effects exerted by sulphur on both gauche and antiperiplanar γ-carbons. The γ-gauche effect of sulphur amounts to 1.6–1.8 ppm, the γ-antiperiplanar effect from practically zero to almost 1 ppm.     

13C n.m.r. chemical shifts in aliphatic alcohols and the γ-shift caused by hydroxyl and methyl groups

Empirical correlations for the prediction of the chemical shifts of the carbon atoms in aliphatic alcohols are presented. Structural and conformational effects contributing to the ¹³C chemical shifts of γ-carbons are discussed.     

Water‐Promoted Generation of a Diazairida Homobarrelene by CC Coupling Between an Iridacyclic Alkylidene and Acetonitrile

The stable cationic iridacyclopentenylidene [Tp^Me2Ir(?CHC(Me)?C(Me)C H₂(NCMe)]PF₆ ( A ; Tp^Me2=hydrotris(3,5‐dimethylpyrazolyl)borate) has been obtained by α‐hydride abstraction from the iridacyclopent‐2‐ene [Tp^Me2Ir(CH₂C(Me)?C(Me)C H₂)(NCMe)]. Complex A exhibits Brønsted–Lowry acidity at the Ir? CH₂ and proximal (relative to Ir? CH₂) methyl sites. The coordination of an extra molecule of acetonitrile to the iridium center initiates the reversible isomerization of the chelating carbon chain of A to the monodentate butadienyl ligand of complex [Tp^Me2Ir(CH?C(Me)C(Me)?CH₂)(NCMe)₂]PF₆, which is capable to engage in a water‐promoted C? C coupling with the MeCN co‐ligands. The product is an aesthetically appealing bicyclic structure that resembles the hydrocarbon barrelene.     

Theoretical study of the effects of substitution,solvation, and structure on the interaction between nitriles and methanol

We report an investigation on intermolecular interactions in R? CN ··· H? OCH₃ (R = H, CH₃, F, Cl, NO₂, OH, SH, SCH₃, CHO, COCH₃, CH₂Cl, CH₂F, CH₂OH, CH₂COOH, CF₃, SCOCH₃, SCF₃, OCHF₂, CH₂CF₃, CH₂OCH₃, and CH₂CH₂OH) complexes using density functional theory. The calculations were conducted on B3LYP/6‐311++G** level of theory for optimization of geometries of complexes and monomers. An improper hydrogen bonding (HB) in the H₃CO? H ··· NC? R complexes was observed in that N atom of the nitriles functions acts as a proton acceptor. Furthermore, quantum theory of “Atoms in Molecules” (AIM) and natural bond orbital (NBO) method were applied to analyze H‐bond interactions in respective complexes. The electron density (ρ) and Laplacian (?²ρ) properties, estimated by atoms in molecules calculations, indicate that H ··· N bond possesses low ρ and positive ?²ρ values, which are in agreement with partially covalent character of the HBs, whereas O? H bonds have negative ?²ρ values. In addition, the weak intermolecular force due to dipole–dipole interaction (U) is also considered for analysis. The examination of HB in these complexes by quantum theory of NBO method fairly supports the ab initio results. Natural population analysis data, the electron density, and Laplacian properties, as well as, the ν(O? H) and γ(O? H) frequencies of complexes, calculated at the B3LYP/6‐311++G** level of theory, are used to evaluate the HB interactions. The calculated geometrical parameters and conformational analysis in water phase solution show that the H₃CO? H ··· NC? R complexes in water are more stable than that in gas phase. The obtained results demonstrated a strong influence of the R substituent on the properties of complexes. Numerous correlations between topological, geometrical, thermodynamic properties, and energetic parameters were also found. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

Substituent effects on 13C NMR chemical shifts in the saturated framework of primary aliphatic derivatives

A general equation describing the effect of substituents on α-carbons in a saturated framework was developed from ¹³C chemical shifts obtained under uniform conditions for selected aliphatic compounds. Experimental correlations for β- and γ-carbons and a discussion of the results are presented.     

Synthesis of Cyclobakuchiols A,B, and C by Using Conformation‐Controlled Stereoselective Reactions

Cyclohexanone with the pMeOC₆H₄ and CH₂?C(Me) substituents at the C3 and C4‐positions was prepared from (+)‐β‐pinene and converted to the allylic picolinate by a Masamune–Wittig reaction followed by reduction and esterification. Allylic substitution of this picolinate with Me₂CuMgBr ? MgBr₂ in the presence of ZnI₂ proceeded with γ regio‐ and stereoselectively to afford the quaternary carbon center on the cyclohexane ring with the CH₂?CH and Me groups in axial and equatorial positions, respectively. This product was converted to cyclobakuchiol A by demethylation and to cyclobakuchiol C by epoxidation of the CH₂?C(Me) group. For the synthesis of cyclobakuchiol B, the enantiomer of the above cyclohexanone derived from (?)‐β‐pinene was converted to the cyclohexane‐carboxylate, and the derived enolate was subjected to the reaction with CH₂?CHSOPh followed by sulfoxide elimination to afford the intermediate with the quaternary carbon center with MeOC(?O) and CH₂?CH groups in axial and equatorial positions. The MeOC(?O) group was transformed to the Me group to complete the synthesis of cyclobakuchiol B.     

1H, 13C and 77Se NMR spectra of substituted selenoanisoles

The ¹H, ¹³C and ⁷⁷Se chemical shifts and the ¹J[C(Me)H(Me)], ^1.2J(SeC) and ²J(SeH) coupling constants in 14 para- or meta-substituted selenoanisoles, R? C₆H₄? Se? CH₃, have been measured and the dependence of these parameters on the electronic effects of the substituent R is discussed. A significant (up to 6 ppm) deviation from additivity of the substituent influence on the shielding of the ¹³C ring carbons has been found.     

13C nuclear magnetic resonance spectra of ethers and glycols

The ¹³C NMR spectra of 21 linear and branched ethers together with the corresponding alcohols have been determined in an attempt to correlate the shieldings in both series. It has been found that the shielding of a carbon in an acyclic ether can be given by the summation of additive shift parameters for substituents and correction parameters for the substitution patterns based on the shielding of the parent alcohol. On examination of solvent-induced shifts for α- and β-carbons in ethers and alcohols, significant ones have been noted in carbon tetrachloride→dimethylsulfoxide and carbon tetrachloride→trifluoroacetic acid. No appreciable concentration-dependent shifts of the shieldings have been observed in both ethers and alcohols. For the shieldings of α-carbons in acyclic glycols, it has been noticed that the observed and predicted values are in accord in 1,3-, 1,4- and 1,5-glycols but deviate in 1,2-glycols. The latter has been examined in a polycyclic system, where the deviations ( > 3·5ppm) in a cis (gauche) 1,2-glycol are larger than those (<2·5 ppm) in a trans (anti-parallel) 1,2-glycol.     

13C NMR spectra of metal σ-cyclopentadienyls

Proton decoupled ¹³C NMR spectra have been measured for the cyclopentadienyl compounds C₅H₅Si(CH₃)_nCl_3?n(n = 1, 2, 3), C₅H₅Ge(CH₃)₃, CH₃C₅H₄Ge(CH₃)₃, C₅H₅Sn(CH₃)₃, σ-C₅H₅Fe(CO)₂-π-C₅H₅ and C₅H₅HgCH₃. A fast metallotropic rearrangement occurring in the compounds causes the spectra to be temperature dependent for the Si, Ge, Sn and Fe derivatives. For the derivatives of silicon or germanium, the olefinic signals are unsymmetrically broadened by the 1,2-shift at lower migration rates. Line widths of the ring carbon signals have been measured to give an estimate for the activation parameters of the rearrangement in C₅H₅Ge(CH₃)₃ (E_a = 10·7 ± 0·9 kcal/mole, ΔG^? = 13·4 ± 0·9 kcal/mole) and C₅H₅Sn(CH₃)₃ (E_a = 6·8 ± 0·7 kcal/mole, ΔG^? = 7·1 ± 0·7 kcal/mole). At room temperature, the spectrum of C₅H₅HgCH₃ displays just one narrow signal responsible for the cyclopentadienyl ligand. The spectrum of CH₃C₅H₄Ge(CH₃)₃ at –30° demonstrates that two isomers containing methyl in the vinylic position are present, the ratio being ca. 2:1. The ¹³C spectra of the vinylic isomers have been analysed in the case of C₅H₅Si(CH₃)_nCl_3?n.     

The influence of methylation on 13C chemical shifts of galactose derivatives

A comparison of the galactose and galactitol spectra with those of methylated derivatives provides the signal assignment of this hexose and its polyol. A formerly stated rule can be confirmed: Methylation of hexopyranose hydroxyls causes upfield shifts of about 4·5 ppm on β-carbons with axial OH groups. In the series of polyols O-methylation causes down-field shifts on the resonance of C_α of about 9–10 ppm, downfield shifts on that of C_β for about 0·6 to 0·9 ppm and upfield shifts of about 0·3 to 0·5 ppm on the C_γ-resonance.     

Carbon-13 fourier transform NMR studies of organotin compounds : III. Carbon-13 chemical shifts and tin-119—carbon-13 spin—spin coupling constants in acyclic,monocyclic and bicyclic organostannanes

Carbon-13 NMR parameters for 33 organotin compounds with a variety of structurul features were investigated in order to obtain information about the relationship between their structure and ¹³C NMR parameters. It was found that the substitution of a proton by a trialkyltin group generally produces an upfield shift for the directly bonded carbon. The γ-nuclei usually resonate at lower fields except where there is appreciable steric strain while the β-carbons undergo relatively constant shifts of approximately 3.5 to 4.5 ppm to lower fields. The magnitude of direct bond coupling Jz-sfnc;¹J(¹¹⁹Sn¹³C)z-sfnc; is influenced by the hybridization of the tin and the directly attached carbon atoms. In rigid organitins, the vicinal coupling constants show a Karplus type variation. In aliphatic organotins, the values of the vicinal¹¹⁹Sn¹³C coupling indicates a flexible molecular framework with a clear cut preference for certain conformations.     

RMN 13C d'Alcynes Aliphatiques: Analyse Topologique des Effets de Substituants Alkyles sur les Déplacements Chimiques des Carbones sp par la Méthode DARC PELCO

Alkyl substituent effects on the sp carbon chemical shifts of aliphatic alkynes have been analysed by the DARC/PELCO method estimating the perturbations linked to the introduction of localized sites in the Limited, Concentric, Ordered Environment of the carbons described by graduate generation from the centre –C?C^.–. A site correlation ‘Topology-δ’ is proposed and its ability to predict the chemical shifts is checked on a population of 55 linear to highly branched alkynes, over a range of 25.2 ppm. This work also shows (i) the independence of the effects of the alkyl groups linked to the C?C bond; (ii) their attenuation with increasing branching of the alkyl substituents; (iii) the small values of the γ_π effects; (iv) the additivity of site perturbation increments (without interaction terms) up to a frontier corresponding to the –C(H,Me,tBu) and –C(Me₂,tBu) groups. A simplified model is derived from a partially ordered generation graph and, for rapid estimation of δ, the global effects of alkyl radicals are expressed as group parameters by summation of their site parameters.     

Electron-impact studies—LI: Hydrogen randomization in the stilbene molecular ion

Hydrozen randomization precedes the formation of M^+· ? H· and M^+· ? CH₃· species from the stilbene molecular ion at 15 eV. The carbon atom involved in the M^+· ? CH₃· elimination originates randomly from the whole molecule. The [M ? 15] ion (m/e 165) in the spectra of stilbene and 9,10-dihydrophenanthrene is produced from a common ion.     

35Cl/37Cl isotope effects on 13C chemical shifts. Assignment of carbon-13 NMR lines of polychlorinated hydrocarbons

An isotope effect of about 0·1 Hz at 25 MHz (0·004 ppm) on the ¹³C chemical shifts due to directly bonded chlorine has been observed at ?50°C for hexachloropropene, hexachlorobutadiene and tetrachlorobutenyne. This effect yields an unambiguous assignment of ¹³C NMR lines to specific carbon atoms in these polychlorinated hydrocarbons.     

Carbon-13 NMR spectra of monosulphones and disulphones: Substitution rules and conformational effects

Carbon-13 NMR spectra have been obtained for 27 aliphatic monosulphones and 13 aliphatic disulphones. Substitution rules have been formulated which allow the prediction of chemical shifts when a CH₂ group in a hydrocarbon is replaced by an SO₂ group, or when an H atom in a sulphone is replaced by an alkyl group. Carbon atoms β to a sulphone group show a marked upfield shift effect which is sensitive to the conformation about the C? S bond; atoms in the trans position experience an upfield shift (?9.39±1.64 ppm) compared with those in the gauche position. An assignment of the meso (m) and racemic (r) β-carbon peaks in di-sec-butyl sulphone was made by synthesis of the optically active compound. |δ_m–δL_r| decreases with increasing temperature for both β–carbon atoms; this effect was interpreted in terms of two available conformers for each of the m and r compounds, those for the m form having the same energy and entropy, and those for the r form having ΔS=0.6 J K^?1 mol^?1 and ΔH=0.8 kJ mol^?1. Observed chemical shifts for the disulphones were compared with those estimated by the application of the first set of substitution rules.     

Darstellung und Charakterisierung von Phthalocyanin-π-Kation-Radikalen von H+, Mg2+ und Cu2+

Preparation und Characterization of Phthalocyanine-π-Cation-Radicals of H⁺, Mg²⁺, and Cu²⁺ The preparation of phthalocyanine-π-cation-radicals (Pc(?1)) of H⁺, Mg²⁺, Cu²⁺ is described. MgClPc(?1) and Cu(NO₃)Pc(?1) · HNO₃ are isolated as stoichiometrically pure, stable redbrown solids. Contrary to the phthalocyanines(?2) (Pc(?2)) these are very soluble with redviolet colour in organic solvents in the presence of R? COOH (R ? H, CF₃, CCl₃). The electronic absorption absorption spectra (UV-VIS) are remarkably solvent-dependent. This solvent effect is due to a reversible radical association. Monomeric radical species exist in nonpolar (CH₂Cl₂), dimeric in polar solvents (CH₃NO₂, C₂H₅OH). The UV-VIS, infrared (IR), and resonance-raman (RR) spectra of MgClPc(?1) and Cu(NO₃)Pc(?1) · HNO₃ are discussed and compared with the analogoues spectra of MgPc(?2) · 2 H₂O and MgPc(?2) · HCl. Although there are only minor differences in the chemical composition and the electronic structure the spectroscopic data vary significantly for every complex. Especially the IR spectrum is suitable for a quick demonstration of the π-cation-radicals. The diagnostic bands are at ca. 1350 and 1450 cm^?1.     

Poly(hydrogen Fluorides) with the Tetramethylammonium Cation: Preparation,Stability Ranges,Crystal Structures, [HnFn+1]− Anion Homology,Hydrogen Bonding F-H…︁F [2]

The melting diagram of the system (CH₃)₄NF? HF was studied between 50 and 100 mole-% HF and from ?185°C to the respective liquidus temperatures (at most 162°C) by difference thermal analysis aided by temperature-dependent X-ray powder diffraction. The system was found to be quasi-binary with the HF-rich intermediary stable compounds (CH₃)₄NF · 2 HF (melting point 110°C), (CH₃)₄NF · 3 HF (20°C, decomposition), (CH₃)₄NF · 5 HF (?76°C, decomposition), and (CH₃)₄NF · 7 HF (?110°C, decomposition), most of which undergo solid-solid phase transitions. Crystal structures were determined of the low-temperature form of (CH₃)₄NF · 2 HF (stable below 83°C, orthorhombic, space group Pbca, Z = 8 formula units per unit cell), the high-temperature form of (CH₃)₄NF · 3 HF (stable above ?87°C, monoclinic, P2/c, Z = 4), and of (CH₃)₄NF · 5 HF (tetragonal, I4 , Z = 2). The structures are those of poly(hydrogen fluorides) (CH₃)₄N[H_nF_n+1] with homologous anions [H₂F₃]^?, [H₃F₄]^?, and [H₅F₆]^?, respectively, formed by strong hydrogen bonding F? H…?F. The anion [H₅F₆]^? is the first one of this composition established by crystal structure analysis. Its structure can be written as [(FH)₂FHF(HF)₂]^? with four equivalent terminal hydrogen bonds of 248.4 pm and a very short central one of 226.6 pm (F…?F distances) through a 4 point of the space group.     

Carbon-13 NMR spectra of saturated heterocycles: XI—Tetrahydropyrans (oxanes)

The ¹³C NMR spectra of 62 oxanes (tetrahydropyrans) with and without methyl substituents at various ring positions, some of them bearing in addition (or instead) ethyl, vinyl, ethynyl, carbomethoxy and methylol substituents at C-2, have been recorded, and the 294 resulting chemical shifts have been correlated by multiple linear regression analysis. Axial and equatorial α-, β-, γ-, δ-, gem- and vic-parameters for shifts caused by methyl groups at all ring positions, and similar parameters for Et,—CH?CH₂,—C?CH, CO₂Me and CH₂OH groups at C-2, are reported. Standard deviations of the parameters are, in most cases, within 0.3 ppm and the agreement of calculated and experimental shifts is excellent. This is probably the largest parameter set of this type extant. ¹³C NMR spectra of a number of additional substituted tetrahydropyrans, and of 3,6-dihydro-2H-pyrans and 3,4-dihydro-2H-pyrans, are tabulated and discussed.     

RMN du 13C de Composés Méthylés Soufrés

A ¹³C NMR study of a series of methyl sulphur compounds is described. The results are discussed in terms of the deshielding effects on the methyl carbon exerted by –SH, –SMe, –SSMe, –SSEt, –SSMe, –SC(O)Me, –SC(S)Me, –SC(S)SMe. The ¹³C NMR chemical shifts of a series of S-methyl thioesters and dithioesters are compared with corresponding esters and connected with chemical properties.