Shielding effects of a cyclopropane ring

Abstract

A ring-current model has been used to calculate the magnetic anisotropy of a cyclopropane ring. This method has proved to be convenient and rapid for estimating the shielding contribution of a cyclopropane ring to the total chemical shifts of neighboring protons with only the aid of molecular models. Shift contributions calculated on the basis of a ring-current model are applied to over 40 different compounds of known geometry.Cyclopropane rings possess a wide variety of unique chemical and physical properties as a result of bond angle deformation. It has been reported that cyclopropane has a molar susceptibility of -39.9 X 10~6,3 while the value predicted from Pascal's numbers is ca. -32 X 10'6. The enhanced suscepti-(1) This work was supported in part by the National Science Foundation and the Petroleum Research Fund, administered by the American Chemical Society.(2) (a) This investigation was supported in part by National Insti-

Absolute Configuration of the New 3-epi-cladocroic Acid from the Mediterranean Sponge Haliclona fulva

“…Indeed an important delocalisation of the σ electrons in a cyclopropane can exert a considerable influence on the chemical shifts of neighbouring protons. The resulting 1 H chemical shifts are lower than those observed for usual methylenes [ 28 ].…”

Diastereomeric cyclic tris-allenes

“…The tris-adduct has been prepared before using bromoform and potassium t-butoxide and converted into the corresponding hydrocarbon. 22 The stereochemistry of the latter had been established as being all cis since only one three hydrogen doublet was seen, corresponding to the trans-protons of the methylene group between the cyclopropanes. The 13 C NMR spectrum of 4 showed just three lines, confirming this assignment.…”

Nuclear magnetic resonance spectrometry

“…Gas to liquid shifts of nonpolar molecules (217), theory of 31P chemical shifts (218), anisotropic s9Co chemical shifts in Co2(CO)g (219), 170 chemical shifts and hydration rates of cyclic ketones (220), correlations between 13C and 11B chemical shifts for a variety of tetracoordinate boron compounds (221) and evaluation and calculations of fluorine-19 chemical shifts and coupling constants (222)(223)(224)(225)(226) have been discussed. The use of factor analysis in solvent effect studies (227), ring current effects (228)(229)(230)(231)(232), long-range shielding effects (233)(234)(235) and numerous calculations of proton chemical shifts and coupling constants and correlation of proton chemical shifts with molecular properties have been reported.…”