An additivity relation for carbon‐13 chemical shifts in substituted allenes

Abstract

Abstract. An empirical method for the calculation of the carbon chemical shifts of allene carbons is developed. The method is successful in predicting the chemical shifts in a wide variety of substituted allenes. The effect of the electronegativity of substituents, with respect to the chemical shift contributions, is discussed. Experimental chemical shift increment values show a linear correlation with both the calculated diamagnetic shielding effects and the Pauling electronegativities for first row elements of the periodic system directly ,attached to the allene For many years the synthesis and chemical properties of allenes have been a major area of interest in this laboratory*. In our NMR research group we have studied the 'H and

Chemistry of the five-membered zirconacycloallenoids: reactions with unsaturated substrates

“…This compound serves as a reference of an undistorted endocyclic allene that has no residual contact with the remote zirconocene moiety, inside the medium sized ring. Consequently, the central sp-hybridized allene carbon of compound 12 shows a 13 C NMR signal in the typical unperturbed allene range 18 (see Table 2). The reaction of the zirconacycloallenoid 6c with 4-octyne is unusual in the sense that unexpectedly a five membered per-substituted zirconacyclopentadiene product ( We subsequently reacted the tert-butyl substituted zirconacycloallenoid 6b with one molar equiv.…”

Propane Transformation on Zn-Modified Zeolite. Effect of the Nature of Zn Species on Alkane Aromatization and Hydrogenolysis

“…This signal together with the signal at 140 ppm can be reasonably assigned to pentamethylbenzenium cation, 43,44 formed as an intermediate for propane transformation to simple aromatic molecules. Also, the signal at 200 ppm together with the signal at 93 ppm may be alternatively assigned to alkyl-substituted allene intermediates; 45 their formation from σ-allylzinc was suggested at propane transformation to aromatics on Zn/H-BEA. 24 At T ≥ 573 K, the signals from the simple and condensed aromatics are detected at 20.0, 130, and 150 ppm (Figure 4g−i).…”

The Synthesis of Functionalized 3-Aryl- and 3-Heteroaryloxazolidin-2-ones and Tetrahydro-3-aryl-1,3-oxazin-2-ones via the Iodocyclocarbamation Reaction: Access to Privileged Chemical Structures and Scope and Limitations of the Method

“…23 Compound 20 exhibited a signal in its 13 C NMR spectrum at 208.9 ppm, a characteristic of the central carbon of an allene moiety. 24 Intermediate 20 was treated with 2 equiv of I 2 in CH 2 Cl 2 at rt to give, after workup and chromatographic purification, 72% of the desired 5-(1-iodoethen-1-yl)-3-phenyloxazolidin-2-one 22 along with 13% of recovered 20. Attempts to increase the conversion by adding a third equivalent of I 2 led to a somewhat lower yield (63%) of the desired product.…”