摘要:

AbstractThe77Se,13C and1H NMR spectra of the products of phenylselenenyl azide and chloride addition to methylenecyclohexane and cyclohexene are presented. Scalar couplings between77Se and1H/13C allowed the absolute assignment of the regioisomers in the1H and13C spectra. Low‐temperature77Se NMR was used to determine the conformer ratios for 1‐azidomethyl‐ and 1‐chloromethyl‐1‐phenylselenenylcyclohexane anti‐Markovnikov addi

ISSN:0749-1581    

DOI:10.1002/mrc.1260320502

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

Abstract13C spin‐lattice relaxation times (T1) and nuclear Overhauser enhancements (NOEs) were measured for individual carbons in flexible‐chain molecules consisting of a hydrocarbon chain attached to fluorene moiety at position 3 through an ester bond. Quantitative treatment of the relaxation data of the ring carbons revealed an anisotropic motion for all the molecules studied. The relaxation times of the chain carbons were analysed in terms of a correlation function describing multiple internal rotations about successive CC bonds. The results (rotational diffusion constants) were used to discuss features of the chain mobility as a function of chain length and chain unsaturation. The assumptions involved in the quantitative treatment were examined and the values were compared with those ofn‐alkanes and lipid b

ISSN:0749-1581    

DOI:10.1002/mrc.1260320503

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractNMR microscopic imaging is shown to be an excellent probe of the freezing and thawing phenomena of liquids in heterogeneous chemical systems, and, in addition, is capable of monitoring the freezing‐thawing of mixed solvent systems. In the model mixed solvent system Me2SO–water, the chemical shift specific slice selective (C4S) imaging technique is used to obtain the spatial distributions of the concentrations and mobilities of the two individual solvents in test samples. Measurements of relaxation parameters make it possible to choose values of imaging parametersTEandTRto ensure quantitative reliability of the images. Images of test samples generated at various temperatures demonstrate the qualitative relationship between image intensity and the Me2SO–water phase diagram. This series of experiments verifies that NMR microscopic imaging will be a powerful tool for the study of liquids within solid matrices, and in particular of cryoprotectant solvents in biological sy

ISSN:0749-1581    

DOI:10.1002/mrc.1260320504

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

Abstract1H,13C,14N and15N NMR methods were applied to the study of some Type A mesoionic 1,3‐diphenyltetrazoles with various exocyclic groups. The ring structures of these tetrazoles are confirmed by the nitrogen NMR data. The shielding of N‐4 increases consecutively by amounts ofca10 ppm as the bonded exocyclic atom changes from S to C t

ISSN:0749-1581    

DOI:10.1002/mrc.1260320505

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractDeuterium isotope effects on13C nuclear shielding,nΔC(D), transmitted across a D‐labelled nitrogen atom were investigated for a series ofpara‐substituted benzanilides. The two two‐bond isotope shifts,2ΔC(D) are perturbed essentially in a trough‐bond manner by change of the contribution of mesomeric structures. The magnitudes of2Δ(CO) and2Δ(C‐1′) are found to be mutually interdependent as evidenced by the linear relationships between the average values of2Δ(CO) and2Δ(C‐1′) with1H(NH) chemical shifts and with15N SCS. This behaviour is interpreted as resulting from a cross‐conjugated transmission pathway involving the carbons shar

ISSN:0749-1581    

DOI:10.1002/mrc.1260320506

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe11B and2H spin–lattice relaxation times,T1, were measured for sodium cyanoborohydride (BH3CN−) and sodium cyanoborodeuteride (BD3CN−) in methanol–ethylene glycol solution as a function of temperature. Both11B and2HT1minima were observed, yielding11B and2H nuclear quadrupolar coupling constants, χ, of 766 and 104 kHz, respectively. Measurement of the14NT1at 300 K gave a χ(14N) value of 2.8 MHz. Electric field gradients were calculated usingab initiomolecular orbital theory, in order to obtain theoretical11B,14N and2H χ values. The values of 847 kHz, −3.25 MHz and 141 kHz for11B,14N and2H, respectively, are larger than those found

ISSN:0749-1581    

DOI:10.1002/mrc.1260320507

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractVariable‐temperature studies in addition to 2D exchange and NOE measurements on the chiral allyl complex [Pd(η3‐Ph2CCHCHPh){(−)‐sparteine}] [PF6] have revealed that there is restricted rotation about theipso‐Callyl‐C bonds for the three Ph groups of the η3‐Ph2CCHCHPh ligand, with that for theantiPh group having a much higher activation energy. Possible consequences for the reaction chemistry of 1,1‐diphenylallyl complexes due to the close proximity of thisantiPh to the chiral bidentate nitrogen ligand are discussed. Detailed13C and1H assignments, based on NOESY, TOCSY and C,H correlat

ISSN:0749-1581    

DOI:10.1002/mrc.1260320508

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

Abstract125Te,19F and13C NMR data for 33 compounds containing tellurium substituents are presented. The125Te chemical shifts in (PhTeCl2)R compounds are between δ = 878 and 1023; in corresponding (PhTeF2)R compounds they are 220 to 360 ppm larger. Effects of substituents and conformational interconversions (dynamic125Te NMR) are discussed. Several diastereomers were identified in (PhTeCl2)R derivatives which are stable at room temperature and differ in the configuration at the tellurium atom (restricted pseudo‐rotation). It is shown that125Te is a well suited nucleus for chiral recogniti

ISSN:0749-1581    

DOI:10.1002/mrc.1260320509

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractAll four fully aromatic isothiazolopyridine isomers have been synthesized, their13C spectra have been assigned and all one‐bond and long‐range13C1H coupling constants have been deter

ISSN:0749-1581    

DOI:10.1002/mrc.1260320510

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractIn the past year, two complete analyses of the proton NMR spectrum of β‐pinene have appeared from different laboratories. The assignments of the chemical shifts to the protons on carbon‐3 were consistent in both studies although there was disagreement in the values assigned to the coupling constants associated with these protons. A molecular modeling study shows β‐pinene to exist in a single conformation. The proton spectrum has been re‐examined with the aid of the Ag(fod)–Yb(fod)3reagent, and the coupling constants redetermined. The results are consistent with the modeling results and confirm that the existing assignments for the C‐3 protons shoul

ISSN:0749-1581    

DOI:10.1002/mrc.1260320511

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY