Conformational analysis by nuclear magnetic resonance. Shift reagent studies on acyclic alcohols. Proton and carbon-13 spectra of the six-carbon aliphatic alcohols

Abstract

The proton spectra of all 18 possible six-carbon aliphatic alcohols have been examined with ten increasing concentrations of Eu(dpm)3 and the 13C spectra examined with four increasing concentrations of Yb(dpm)3. Utilizing the McConnell-Robertson equation, the average solution conformations of these alcohols in CS2 have been determined by both methods of spectroscopy and have been found to be the same. Experimentally, the use of Yb(dpm)3 and 13C spectroscopy has several advantages. The problem of distortion of the substrate by the shift reagent is considered in detail. The many pitfalls of this type of analysis are discussed. A linear regression analysis of the 13C chemical shifts of the 95 nonequivalent resonances in the 18 alcohols has been performed. Large correction factors in the I3C shifts are indicated for adjacent tertiary and quaternary carbons. Comparisons are made between the 13C chemical shifts of these alcohols and conformationally similar fragments of cyclohexanols. The 13C shifts of diastereotopic methyl groups are considered in detail.

An Unsaturated Four‐Coordinate Dimethyl Dimolybdenum Complex with a Molybdenum–Molybdenum Quadruple Bond

“…In 1974, the pyrophoric salt [Li(thf)] 4 [Mo 2 Me 8 ] was prepared by Cotton, Wilkinson, and co‐workers and found to exhibit a Mo–Mo bond distance of 2.148(2) Å and Mo–Me bond lengths in the approximate range 2.27–2.31 Å . The structures of neutral complexes of composition [Mo 2 Me 4 (PR 3 ) 4 ] (PR 3 =PMe 3 , PMe 2 Ph) were later determined, and featured similar Mo–Mo (ca.…”

Stereocontrolled synthesis, conformational features, and response to thermal activation of the seven possible bis- and trishomocycloheptatrienes

“…The Cv symmetry of 14 is clearly revealed by its 13C (five signals) and NMR spectra supported by appropriate Eu(fod)3 shift studies. 14 The stereochemical reversal which results in the formation of 15 appears to be the result of steric congestion on the syn face of 13 and not to unusual conformational factors such as those encountered in medium-ring allylic alcohols. 15 If this hypothesis is correct, the problem of reversing the directionality of this reaction so as to obtain 15 with high stereochemical control reduces to substitution of the hydroxyl function.…”

Computer program for the retrieval and assignment of chemical environments and shifts to facilitate interpretation of carbon-13 nuclear magnetic resonance spectra

“…a Explained in text and Table III. 6 For some main groups, substituents more than one bond away are considered «-substituents; see Table I.c A blank space represents zero, a 0 means ten, and the shift characters of 1-9 (! "#$%&'()) represent eleven through nineteen.…”

“…Probably the 0 = 0 + ) (1) most generally useful and accurate example of this approach is the Lindeman and Adams method (3) for carbons in acyclic alkanes, whereby the calculations predict chemical shifts with a standard error of 0.79 ppm when applied to the compounds from which the parameters were derived. At a comparable level of accuracy are methods which apply to acyclic saturated amines (4) and alcohols (5,6), and numerous other sets of parameters have been derived for other types of compounds (1,2). The latter are less generally useful and/or less accurate in their predictions, with errors of up to 3 ppm not uncommon.…”