Ring size shift

For cyclic carboxylic acid derivatives, decreasing ring size shifts a carbonyl absorption to higher frequencies. 

There is no separate shift conversion system and no recycle of product gas for temperature control (see Figure 1). Rather, this system is designed to operate adiabatically at elevated temperatures with sufficient steam addition to cause the shift reaction to occur over a nickel catalyst while avoiding carbon formation. The refractory lined reactors contain fixed catalyst beds and are of conventional design. The reactors can be of the minimum diameter for a given plant capacity since the process gas passes through once only with no recycle. Less steam is used than is conventional for shift conversion alone, and the catalyst is of standard ring size (% X %= in). 

A useful comparison of the 13C shifts for acyclic and cyclic five- and six-membered sulfur compounds has been made86,220, but data on cyclic sulfur compounds of other ring sizes are rather limited. Typically, oxidation of sulfide to a sulfone results in 20-25 ppm... 

All cyclic compounds of types 83-88 have been characterized by their diagnostically simple and C-NMR spectra. Some general regularities can be observed, namely, a small but steady upfield shift in the C-NMR spectra of the carbon signals of the polyacetylenic macrocycle with increasing ring sizes. 

An important result of the multinuclear NMR investigations of 23— 25, 27, 28, and 31-35 is that the structures, in contrast to aggregates of monometalated secondary phosphanes and arsanes, are retained in solution. Thus, the phosphandiide derivatives here discussed show resonance signals in their 31P NMR spectra that are independent of concentration and temperature (see Table III). The 31P and 27A1 NMR chemical shifts of 23-25, 27, and 31-35 differ with respect to ring size of the clusters and electronic influences by the substituents at phosphorus and aluminum. 

In the case of 1,3-butadiene, the chemical shifts of inner (H2, H3) protons and outer (HI, H4) is large, while in the case of cycloalkadienes (e.g. 1,3-cyclopentadiene and 1,3-cyclohexadiene), the difference is very small. It is interesting to note that in 1,3,5-cycloheptatriene, the chemical shifts of three kinds of olefinic protons are very diverse. The effect of the ring size and in the chemical shifts of radialenes was also included. 

In order to explore the significance of the term in determining Aa, Musher (1962) calculated its effect for the C7H7 and CsHs ions and found that the correlated points provided a near perfect fit with a correlation line of slope 11-2. Fraenkel et al. (1960) introduced a correction for the variation of ring current with ring size and found it to be small. In Table 1, the raw data for the pnmr shifts for these ions as well as some other monocyclic aromatic ions are given, along... 

Comparison of the chemical shift data (Table 1) reveals that the peak positions of a and 6 carbons of 20-crown-4 are quite different from the corresponding carbons of THF or the polymeric PTME. Small but distinct chemical shift differences were also found for macrocyclic oligomers of other ring sizes. 

Table I. Assienment of ring size bv the observation of the 13°-n.m.r. chemical shift of the orthoester (or acetal) carbon atom...

Ideally, the Stanger demonstration should be an expression of the stretch-bend interaction in the Bj normal mode in benzene. Thus, it is instructive to examine the nature of the stretch-bend interaction in typical monocyclic and bicyclic alkenes. The IR spectra of monocyclic and bicyclic alkenes shift hypsochromically for exomethylenes and bathochromically for endocyclic alkenes with decreasing ring size. " This effect has been shown to be dominated by mode-coupling for the monocyclic series, but consistent with a pure angular effect or the bicyclic series.Further investigation in this vein is likely to resolve the paradox initiated by Stanger s work. 

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