Chemical shifts alicyclic rings

Substituents on both sides of the double bond are considered separately. Additional vinyl carbons are treated as if they were alkyl carbons. The method is applicable to alicyclic alkenes in small rings carbons are counted twice, i.e., from both sides of the double bond where applicable. The constant in the equation is the chemical shift for ethylene. The effect of other substituent groups is tabulated below. 

When CH2F is a substituent on most alicyclic rings, such as a cyclohexane ring, the 19F chemical shift of this group is not significantly altered from that of an acyclic system (Scheme 3.2). On the other hand, when it is attached to a cyclopropane ring, a unique deshielding influence is observed. 

Scheme 6.26 provides chemical shifts for all of the fluorines in a representative group of perfluorocarbons. The various environments exhibited should allow one to estimate the chemical shift for almost any fluorine in a perfluorocarbon system. The fluorine chemical shifts of four-, five- and six-membered ring perfluoroalicyclics are quite consistently in the range of -133 to -134 ppm, but as usual, fluorines on a cyclopropane ring appear at a much higher field than those of other fluorinated alicyclics, perfluorocyclopropane having a chemical shift of -159 ppm. 

Miyamoto and Yamazaki elaborated a general synthetic method to spiro-substituted [l,2,4]triazolo[l,5-c]pyrimi-dines bearing alicyclic rings of different sizes and bearing different (amino and sulfano) substituents in position 5 <1997JHC871>. 13C NMR chemical shifts of the ring carbon atoms of some selected derivatives are compiled in Table 4. 

Fulvic acid isolated from Island Lake provided direct spectral evidence of protons attached to aliphatic alicyclic rings. The H NMR spectrum of this sample (Figure 3) has a broad medium-intensity peak near 1.8 ppm. The chemical shifts of protons on aliphatic alicyclic rings are commonly split into two broad peaks centered at 1.1 and 1.8 ppm because of their variable boat and chair configurations (23). 

APPENDIX C CHEMICAL SHIFTS IN ALICYCLIC AND HETEROCYCLIC RINGS... 

Chemical Shifts in Alicyclic and Heterocyclic Rings Table 3.5 Chemical shifts in Alicyclic Rings... 

The measurement of chemical shifts in alicyclic hydrocarbons also provides information regarding the conformational preference of substituted rings. The chemical shifts of the carbinol carbon atom... 

Not surprisingly, the increasing structural importance of n.m.r. in structural alicyclic chemistry has produced a number of papers dealing with simple five- and six-membered ring systems. For example, in a survey study of the conformational and substituent dependence of coupling constants, the chemical shifts and observed couplings in methyl-enriched cis and Irons (as a 50 50 mixture) 4-t-... 

H-Chemical Shifts (6 in ppm relative to TMS) and Coupling Constants (J in Hz) in Alicyclic Rings Condensed with Aromatic Systems... 

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