Natural Abundance 17O NMR Study of Substituted α,α,α-Trifluoromethoxybenzenes

Natural abundance ¹⁷O NMR chemical shift data for meta- and para-substitued α,α,α-trifluoromethoxybenzenes recorded in acetonitrile at 75° C are reported. The ¹⁷O NMR signals for the trifluoromethoxy compounds are deshielded by greater than 65 ppm compared to analogous methoxy compounds. A quantitative relationship between ¹⁷O NMR chemical shifts for the trifluoromethoxy and methoxy benzenes is reported.     

Natural Abudance 17O NMR Studies of Thiol Esters and Related Analogs

Natural abundance ¹⁷O NMR data for a series of thiol esters and related analogs are reported. The carbonyl signal of the thiol esters range from 463 ppm to 514 ppm; these values are downfield of their oxygen analogs by ca. 150 ppm. A linear relationship between the ¹⁷O NMR chemical shift of the thio-compounds and their oxo-analogs is observed.     

Hydroxyl Substituent Chemical Shift (SCS) Effects in Alcohols: The 17O NMR of Diols

The ¹⁷O NMR spectra for a series of saturated diols were investigated. From these studies both hydroxyl induced substituent chemical shift (SCS) effects of hydroxyl oxygen ¹⁷O NMR chemical shifts were determined. In addition, linear correlations between the ¹⁷O chemical shift of the hydroxyl oxygen (ROH) and the ¹³C chemical shift for the methyl group in the corresponding hydrocarbon (RCH₃) were obtained.

     

17O and 13C NMR Studies of Isobenzopyrylium Salts

¹³C and ¹⁷O NMR chemical shifts for a series of isobenzopyrylium salts are reported. The oxygen signal range from 300 to 270 ppm as a double bonded carboxylic oxygen, From the ¹⁷O and ¹³C data valuable informations on the conjugative and substituent effects of isobenzopyrylium salts were obtained.     

取代苯乙酮羰基17O-NMR化学位移的研究

提出计算取代苯乙酮羰基¹⁷O-NMR化学位移的公式：δ_cal=550.0+Δo+Δm+Δp，通过线性回归法确定了12种取代基参数.以44种取代苯乙酮为样本点作回归检验表明该公式的置信度为99.5%，计算值与实验值的偏差Δδ在5.0（相对误差约0.5%）以内的羰基¹⁷O-NMR化学位移的计算值在90%左右.     

Oxygen-17 NMR Spectroscopy: Effect of Substituents on Chemical Shifts and Width Line in Ortho Substituted Nitro Benzenes

¹⁷O-NMR spectra, of ortho, meta and para substituted nitrobenzene are reported. The ¹⁷O nucleus of NO₂ group in ortho derivatives absorb at lower field that meta and para compounds. Moreover, width line of ¹⁷O resonance appears to be strongly dependent by substituent position. The ¹⁷O chemical shifts are correlated with U. V. spectra and X-ray diffraction data.     

Structural Assignment of Stilbenethiols and Chalconethiols and Differentiation of Their Isomeric Derivatives by Means of 1H‐ and 13C‐NMR Spectroscopy

Abstract

The ¹H‐ and ¹³C‐NMR spectra of some substituted stilbenes and chalcones were assigned unambiguously on the basis of a combination of homo‐ (COSY) and heteronuclear (HETCOR) two‐dimensional methods, the chemical shifts, as well as spin‐coupling constants. The A_ik empirical parameters of the –O–C(S)–N(CH₃)₂, –S–C(O)–N(CH₃)₂, and –SH group were calculated to help predict the chemical shifts of substituted stilbenes, 4′‐nitrostilbenes, and chalcones. The ¹H‐ and ¹³C‐NMR spectra have been shown to be able to differentiate between the isomers of O‐stilbenyl (4, 5) and S‐stilbenyl N,N‐dimethylthiocarbamates (7, 8) as well as O‐chalconyl (6) and S‐chalconyl N,N‐dimethylthiocarbamates (9).     

取代苯甲酰胺的羰基17O-NMR化学位移研究

按取代苯甲酰胺、取代N-甲基苯甲酰胺、取代N,N-二甲基苯甲酰胺三类,提出了计算这三类化合物中羰基¹⁷O-NMR化学位移的公式：δ_cal(¹⁷O)=δ_0n+C×ΣΔ,并通过线性回归法结合最小二乘法得到11种取代基参数,计算结果用以上三类化合物的33个羰基¹⁷O-NMR化学位移数据为样本点作回归检验,置信度为99.5%,计算误差Δδ小于1.0（相对误差小于0.1%）的¹⁷O-NMR化学位移计算值占90%以上.     

MOLECULAR STRUCTURE OF HETEROCYCLES: 17O NMR CHEMICAL SHIFTS: TORSION ANGLE RELATIONSHIPS IN 3-ALKYL SUBSTITUTED 4,5-DIHYDROISOXAZOLES AND ISOXAZOLES†

A quantitative relationship between the ¹⁷O substituent chemical shifts (SCS) of γ-alkyl substituents and the torsion angles calculated by the AM1 method is reported. A series of 3-alkyl substituted 5-trichloromethyl-5-hydroxy-4,5-dihydroisoxazoles and 5-trichloromethyl isoxazoles [where 3-alkyl substituents are Me, Et, n-Pr, iso-Bu, BrCH₂, iso-Pr, Br₂CH and tert-Bu] as model compounds were used.

     

13C NMR Chemical Shifts Substituent Effects of (E)- and (Z)-N-ethyl-N-Methylamides

Carbon-13 NMR chemical shifts of a series of (E)- and (Z)-N-ethyl-N-methylamides [RC(O)NEtMe, R=H, Me, Et, i-Pr, t-Bu, CF₃, ClCH₂, Cl₂CH, Cl₃C, BrCH₂, Br₂CH, Br₃C and ICH₂] are reported. The α-carbon and carbonyl carbon chemical shifts are correlated with the empirical α-substituent effect and Charton's electrical parameter ([sgrave]_I), respectively. The N-alkyl carbon resonances were attributed mainly to the γ- and δ-effects of R.     

Determination of the Stereochemistry of Substituted 5-Methylenehydantoins and Thiohydantoins by 13C NMR and Homonuclear NOE Experiments

Basically the aim of this work is to define the accurate configuration of the exocyclic double bond of substituted 5-methylenehydantoins and thiohydantoins which have been conceived as potential Aldose Reductase inhibitors. A previsional survey based upon the chemical shifts analysis from ¹H and decoupled ¹³C NMR spectra discloses, for a part of the family of compounds, the assignment of the Zconfiguration for unsubstituted (2,3) and N-3 substituted (6,7,9) derivatives, and the E-configuration for the N-1 substituted (8,11) ones. The qualitative study with Homonuclear NOE (8,11) and the coupling constant measuring ^{3 J}C4-C=C-H6 from coupled ¹³C NMR (1–11), lead to the assignment of the accurate configuration of the whole family's compounds in agreement with the previsional study.     

13C NMR Chemical Shift of β-Alkoxyvinylketones: II. Empirical Substituent Effects in β-Aryl-β-Methoxyvinyltrihalomethylketones

Evaluation by empirically derived equations for the substituent effect (α,β,γ,δ) on the ¹³C NMR chemical shifts for C-1, C-2, C-3 and C-4 in β-aryl-β-methoxyvinylhalomethylketones 1a-g to 2a-g [R³C(O)-CH=C(Ar)-OMe, where R³ = CCl₃, CF₃ and Ar = p-YC₆H₄ (Y = H, Me, MeO, F, Cl, Br, NO₂)], taking as reference the β-ethoxyvinyltrichloromethylketone (3), is reported. From the calculated values for the α,β,γ,δ effects for each substituent it was possible to estimate the chemical shift of each carbon of the compounds 1,2. The ¹³C chemical shifts of the C-1, C-2, C-3, C-4 of these compounds, can be estimated with good to rasoable precision: 84% of the calculated chemical shifts are found to be within ±1.0ppm, and 100% are found to be within ±1.5ppm. The Y-Effects on C-3 and C-4 are compared with carbon charge densities (qr).     

取代苯甲酸甲酯羰基17O-NMR化学位移研究

提出了计算取代苯甲酸甲酯类化合物羰基¹⁷O-NMR化学位移的公式：δ_cal(¹⁷O)=337.3+Δo+Δm+Δp, 根据52种取代苯甲酸甲酯类化合物的52个羰基¹⁷O-NMR化学位移数据, 通过线性回归法结合最小二乘法求得22个用于该公式的取代基参数, 回归检验表明采用该公式计算结果的置信度为99.5 %,计算值与实验值的偏差Δδ在5.0以内的～100 ％.     

Acyclic Analogues of Purine Nucleosedes: One- and Two-Dimensional 1H and 13C NMR Evidences for N-9 and N-7 Regioisomers

It has been established by means of one-and two-dimensional ¹H and ¹³C NMR Spectroscopy that adenine acyclonucleosides are substituted at either N-9 or N-7 with 2',3'-dihydroxyprop-1-yl (2 and 3) or 2'-hydroxyprop-1-yl (4 and 5) aliphatic chains. The N-3 isomer has not been formed, as claimed previously. This was deduced on the basis of chemical shifts, substituent induced chemical shifts, magnitude and multiplicity of C-H couplings as well as connectivities in 2D homo-and heteronuclear correlation spectra.     

13C NMR Chemical Shifts of β-Alkoxyvinyl Ketones: III✠-Empirical Substituent Effects in 1-Alkylamino-6-Ethoxy-1,5-Hexadien-3,4-Diones and 1,6-bis(Alkylamino)-1,5-Hexadien-3,4-diones

Evaluation by empirically derived equations for the substituent effect (E_Xn and E_Yn, n = 1 to 6) on the ¹³C NMR chemical shifts for C-1, C-2, C-3, C-4, C-5 and C-6 in 1-alkylamino-6-ethoxy-1,5-hexadien-3,4-diones 1a-f and 1,6-bis(alkylamino)-1,5-hexadien-3,4-diones 2a-f [XCH=CHC(O)-C(O)CH=CHY, where X, Y = OEt, NH₂, PhCH₂NH, n-BuNH, i-PrNH, cyclo-C₆H₁₁NH, t-BuNH], taking as reference the 1,6-diethoxy-1,5-hexadien-3,4-dione (3), is reported. From the calculated values for the E_Xn and E_Yn effects for each substituent it was possible to estimate the chemical shift of each carbon of the compounds 1,2 with excellent precision: 100% of the calculated chemical shifts are found to be within ±0.5ppm. The carbon-13 chemical shifts of C-1, C-2 and C-3 of compounds 1a,2a,3 led a good correlation with carbon charge densities (qr).     

A 13C-NMR Study of Some 9-Ahinoacridines and Their Cations in Relation with Tautomaric Problems

¹³C-NMR chemical shifts have been measured for some 9-aminoacridine derivatives, substituted on positions 9 and 10, in DMSO and for some related salts in D₂O. The results are discussed with regard to amino/imino tautomerism, structure of the cations, and slow rotation about a formal C-N double bond.     

1H and 13C NMR Spectral Study of Some 2r-Aryl-6c-phenylthian-4-ones,Their 1-Oxides and 1,1-Dioxides

ABSTRACT

Four 2r-aryl-6c-phenylthian-4-ones 1b?1e and their 1-oxides 2b?2e and 1,1-dioxides 3b?3e have been newly synthesized. ¹H and ¹³C NMR spectra have been recorded for all these compounds and 2r,6c-diphenylthian-4-one 1-oxide 2a. ¹³C NMR spectrum has been recorded for the sulfone 3a of 1a. For selected compounds ¹H-¹H COSY, HSQC, HMBC, and NOESY spectra have been recorded. The vicinal proton–proton coupling constants suggest that in all these compounds, the heterocyclic ring adopts chair conformation with equatorial orientations of the aryl and phenyl groups. Proton and carbon chemical shifts suggest that in the sulfoxides, the S=O bond is axial and enhances the J _aa value by some special effect. The S = O bond causes a significant upfield shift even on carbons without hydrogens. Significant solvent shifts also were observed.     

A 15N NMR Study of Some Imidazolidine-2,4-Dichalcogen Derivatives

The ¹⁵N NMR chemical shifts and ¹(¹⁵N-¹H) coupling constants of a series of imidazolidine-2,4-dichalcogen (O, S) derivatives are reported.The ¹⁵N NMR chemical shifts show a linear correlatlon wlth the vNH stretchlng vlbratlons. The influence of the substitution of the oxygen at C₂ and/or C₄ with the sulphur, and of the hydrogen at C₅ wlth the methyls and phenyls has been considered. The ¹J(¹⁵N-¹H)'s found In thls serles of molecules agrees well with the expected values.     

13C NMR Chemical Shifts of Heterocycles: Empirical Substituent Effects in 5-Halomethylisoxazoles

Evaluation by empirically derived equations for the Substituent effect (α, β, γ, δ) on the ¹³C NMR chemical shifts for C-3, C-4. C-5 and halomethyl-substituent carbon (C-6) in isoxazoles 1-5 [where C-3 substituent (R¹) = H, alkyl or phenyl, C-4 Substituent (R²) = H, alkyl, and C-5 substituent (R³) = di-or trihalomethyl, methyl and H], taking as reference the compound la, is reported. From the calculated values for the α, β, γ, δ effects for each substituent it was possible to estimate the chemical shift of each carbon of the compounds 1–5. The ¹³ C chemical shifts of the C-3, C-4, C-5, C-6 of these compounds, can be estimated with good precision: 94% of the calculated chemical shifts are found to be within ±1.0ppm, and 100% are found to be within ±1.5ppm.     

Vibrational Spectra of 4-Benzoylpiridine and the 18O Substituted Derivative

Abstract

Infrared and Raman spectra of 4-benzoylpiridine (4BP) and its ¹⁸O substituted derivative have been recorded in the solid and in the molten state. Polarized Raman spectra in the molten state have also been measured. The assignment of the vibrational bands is performed on the basis of isotopic shifts, group vibrational concept and polarization features of the normal modes. The previous assignment of the in- and out-of-plane deformations of the carbonyl group and the fundamentals below 700 cm^?1 are questioned and corrected.