Studies on tacticity of polyacrylonitrile. II. High-resolution nuclear magnetic resonance spectra of 2,4-dicyanopentanes

The NMR spectra of 2,4-DCNP were measured in CCl₄, NaCNS–D₂O, DMSO-d₆, and other solutions. The spectra of the meso form show no significant change with the solvent, but the racemic form shows two kinds of spectra, one of which is observed in a solvent for PAN and the other in a nonsolvent. In the solution, the meso 2,4-DCNP is considered to have two equivalent conformations, TG and G'T, which are the mirror images with each other. The racemic 2,4-DCNP, however, might have predominantly either the TT or GG conformation in CCl₄, pyridine, and benzene, while it has the two conformers with almost equal probability in NaCNS–D₂O and DMSO-d₆. The results obtained from the calculation assuming appropriate constants are in fairly good agreements with the observed spectra of the 2,4-DCNP isomers. The values of chemical shifts and coupling constants used in the calculation correspond to those of PAN which were obtained previously from the analysis of the NMR spectra.     

Studies on the tacticity of polyacrylonitrile. III. NMR spectra of stereoisomers of 2,4,6-tricyanoheptane as model compounds of polyacrylonitrile

The three stereoisomers of 2,4,6-tricyanoheptane were separated and their NMR spectra were studied as the three-unit model compounds of polyacrylonitrile. The chemical shifts and coupling constants obtained from the NMR spectra were compared to those of the two-units model compounds. The geminal protons for the isotactic methylene are not equivalent, but the difference of the chemical shifts is smaller than that in the meso two-unit model. The racemic methylene signals appear at higher field than the meso methylene in the heterotactic three-unit model as in the case of the racemic and the meso two-unit models. The signals of the methinic protons in triads appear in the order: isotactic CH, heterotactic CH, and syndiotactic CH from the high field. From the observed values of the vicinal coupling constants, the chain conformations of the model compounds are also discussed.     

High-resolution nuclear magnetic resonance spectra of phenanthrenes–IV Phenyl derivatives of phenanthrene

Proton magnetic resonance spectra at 60 MHz are reported for 9, 9′-biphenanthryl, 1-phenylfluoranthene, 9-benzylphenanthrene, 1-, 4- and 9-phenylphenanthrenes and 9-methyl-10-phenylphenanthrene, all in CS₂ solution. Approximate values of some of the chemical shifts and coupling constants were extracted from the overlapped and often collapsed AB, ABC ABCD and AA′BB′C (phenyl) spin systems. By comparison with data for phenanthrene itself, estimates have been made for the dihedral angle, θ, between the planes of the phenyl ring and the phenanthrene nucleus in phenylphenanthrenes. These lead, except for 9-phenylphenanthrene for which the angle derived from H(10) by PMR is higher than UV suggests, to plausible values for θ: 90°, 75°, 40° and 45 to 60°, for 4-phenyl, 9-methyl-10-phenyl-, 1- and 9-phenylphenanthrenes, respectively.     

Triad tacticity of polyacrylonitrile

The high-resolution NMR spectra of polyacrylonitrile-β,β-d₂ prepared by radical polymerization were determined, and the stereoregularity of the polymer was studied. The NMR spectra of methine protons of polyacrylonitrile-β,β-d₂ in dimethyl sulfoxide-d₆ and a mixture of nitromethane-d₃ and ethylene carbonate showed three partially resolved multiplets. The deuterium-decoupled spectra of the polymer were measured, and three well resolved peaks were observed in the two solvents and dimethylformamide-d₇. These three peaks were analyzed by comparison with the NMR spectra of model compounds and polyacrylonitrile-α-d, and they were assigned to isotactic, heterotactic, and syndiotactic triads with decreasing magnetic field. This order seems to be unchanged in other solvents. Triad stereoregularity of the polymer was determined according to the assignment. Polymerizations of acrylonitrile-β,β-d₂ by radical initiators between ?78°C and 60°C were explained by the Bernoulli trial propagation step. The polymers had an atactic structure, independent of polymerization temperature. This shows that in free-radical polymerization of acrylonitrile, the chain end is not represented as having any particular stereochemistry. Other stereochemical control is necessary to produce tactic polymers. The triad tacticity of isotactic polyacrylonitrile was also determined.     

Nitrogen-15 nuclear magnetic resonance spectra of ketenimines

Nitrogen-15 NMR spectra of 11 ketenimines have been taken both at the natural-abundance level of ¹⁵N and with the aid of ¹⁵N-labeling. The nitrogen chemical shifts are substantially different from those of neutral imines and are upfield, more like those of protonated imines. The results are in accord with significant delocalization of the nitrogen lone-pair. Furthermore, there is a rough parallelism between the ¹³C shifts of the terminal carbons and the ¹⁵N shifts.     

Proton nuclear magnetic resonance spectra ofOrtho-metalated alkyne-carbonyltriosmium complexes

Summary The¹H nuclear magnetic resonance spectra of Os₃(CO)₈(Ph₂C₂)₂ and Os₃(CO)₈[(p-ClC₆H₄)₂C₂]₂ are described. In these metal cluster complexes theortho-metalation involves phenyl groups linked to a cyclopentadiene ring.     

Carbon-13 nuclear magnetic resonance spectra of veratrine components

The ¹³C NMR spectra were determined and signals assigned to the various carbons of veratridine and cevadine.     

Carbon-13 nuclear magnetic resonance spectra of D-homoandrostane derivatives

The ¹³C chemical shift data of a series of ketone, alcohol and ester derivatives of D-homoandrostane are reported. Homologation effects are discussed, as well as substituent effects on the homologated structures.     

Carbon-13 nuclear magnetic resonance spectra of substituted-s-triazolyl tetrazoles

The natural abundance carbon-13 nuclear magnetic resonance spectra of various 5-aryltetrazoles, 1-(5-aryltetrazol-2-ylacetyl)-4-phenyl thiosemicarbazides and 5-(5-aryltetrazol-2-ylmethyl)-4-phenyl-s-triazole-3-thiols were recorded using Fourier transform techniques. The chemical shifts of various carbon resonances have been assigned on the basis of chemical shift theory, the signal multiplicity observed in the single-frequency off-resonance decoupled (SFORD) spectra and comparison with the chemical shifts of the model compounds.     

Carbon-13 nuclear magnetic resonance spectra of methaqualone metabolites

Carbon-13 chemical shifts are reported for methaqualone, seven hydroxylated methaqualone metabolites, and four acetate derivatives. The signals are assigned on the basis of chemical shift theory, SFORD multiplicities, signal intensities, and comparisons with model compounds.     

Carbon-13 nuclear magnetic resonance spectra of phenycyclidine analogs

Natural abundance carbon-13 chemical shifts are reported for the hydrochloride salts of phencyclidine ( 1a ) and sixteen analogs. The signals are assigned on the basis of chemical shift theory, SFORD multiplicities, signal intensities, and comparisons with model compounds. In addition to its forensic value, the data suggests that the solution conformations of the analogs are similar to that of phencyclidine hydrochloride.     

Carbon-13 nuclear magnetic resonance spectra of isoquinoline alkaloids

The ¹³C nmr ehemieal shifts of 1,2,3,4-tetrahydroisoquinoline, salsolidine and laudanosine are reported. The various carbon resonances have been assigned on the basis of chemical shift theory, intensity of the signals, multiplicities generated in SFORD spectra and the comparison with model compounds.     

Carbon-13 nuclear magnetic resonance spectra of ceveratrum alkaloids

The ¹³C NMR spectra were determined and signals assigned to the various carbons of the alkamines veracevine, germine and zygacine derived from steroidal alkaloids of the ceveratrum class. Assignment of signals was aided by analysis of the partially relaxed spectrum of cervagenine 9,12,14-orthoacetate-3, 16-diacetate.