Upfield shift

In order to prove that intramolecular cyclization occurs before telechelic oligomer formation, an experiment similar to previous work by Calderonlf is performed using 14 in place of Calderon s classical catalyst system. Macrocyclic species are formed when a toluene solution of polybutadiene is exposed to this catalyst, supported by both NMR and GC data. The vinylic resonances are clearly shifted upfield from polybutadiene. GC analysis shows macrocyclic trimers and tetramer regioisomers. 

It follows that aromaticity can be determined from an NMR spectrum. If the protons attached to the ring are shifted downfield from the normal alkene region, we can conclude that the molecule is diatropic, and hence aromatic. In addition, if the compound has protons above or within the ring (we shall see an example of the latter on p. 69), then if the compound is diatropic, these will be shifted upfield. One drawback to this method is that it cannot be applied to compounds that have no protons in either category, for example, the dianion of squaiic acid (p. 69). Unfortunately, NMR is of no help here, since these spectra do not show ring currents. ... 

As we have seen (p. 59), these systems are expected to be not only nonaromatic but actually antiaromatic. The chief criterion for antiaromaticity in annulenes is the presence of a paramagnetic ring current, which causes protons on the outside of the ring to be shifted upfield while any inner protons are shifted downfield, in sharp... 

Once coordinated to a metal centre, the signal corresponding to the carbene carbon atom is usually shifted upfield. The chemical shift of the carbene carbon atom (C ) for a given metal in a given oxidation state is usually characteristic (Table 1.1). 

During the homogeneous hydrogenation of a variety of substrates - and in particular of those containing aryl groups - satellites appear in addition to the expected PHIP-NMR spectra of the usual para-hydrogenated products, typically shifted upfield relative to those of the authentic parent compounds [37]. 

Preparative Photolysis. The preparative photolysis of an aqueous solution (pH=8.5) of AETSAPPE (2.5 M) was conducted in a 1-inch diameter quartz test tube in a Rayonet Reactor (Southern New England Radiation Co.) fitted with 254 nm lamps. Within two hours the solution gelled and the reaction was terminated. Upon acidification the solution cleared, and the product could be re-precipitated by addition of base. This indicates loss of the thiosulfate functionality. The product was dissolved in dilute HC1, precipitated with acetone, and filtered. This process was repeated three times, and the final precipitate was washed with water. The product (20 to 30 mg) was dried in vacuo for 24 hours and stored in a dessicator until use. Comparison of the13 C NMR spectrum of the product with the starting AETSAPPE 13C NMR spectrum clearly shows that the thiosulfate methylene peak shifted upfield, from 39 ppm to 35 ppm. The complete 13 C NMR and IR analysis of the product were consistent with the disulfide product. Further, elemental analysis of the product confirmed that the product was the desired disulfide product 2-amino (2-hydroxy 3-(phenyl ether) propyl) ethyl disulfide (AHPEPED) Expected C 58.39, H 7.08, N 6.20, S 14.18 actual C 58.26, H 7.22, N 6.06, S 14.28. 

Due to its high symmetry, 8 exhibits only one signal in its H NMR spectrum (7.81 ppm), and three NMR lines at 127.2 ppm (10 methine rim carbons), 130.8 ppm (5 quaternary rihi carbon atoms), and 135.8 ppm (5 quaternary hub carbon atoms). The proton resonance of 8 is significantly shifted upfield, as compared to coronene 9 (8.9 ppm), which may reflect an influence of the curvature of the carbon network on the ring current. 

Likewise, three resonances can be also observed in the Si NMR spectrum of 2, but in this case the resonance of the outermost silicon atoms directly bonded to the ferrocenyl moiety is shifted upfield and occurs at -3.0 ppm. 

The degree of dimer formation via a methylene linkage (crosslinking) was estimated by the coefficient of the integrals of the proton NMR spectra of methoxy groups situated adjacent to the newly formed bond—of which the resonances are shifted upfield (63.4-3.7)—and that of the total methoxy resonances (63.4-4.0). 

The NMR spectrum shows that the methyl groups are strongly shifted upfield. They appear at 6 0.5 ppm from TMS as reference. We can explain this by the stronly hindered polysulfide, which causes the methyl groups to be located In the shielding cone of the phenyl rings. 

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