NMR study of diastereoisomerism of 2-(1-aminoethyl)bicyclo[2.2.1]heptane and its hydrochloride (deitiforin) (original) (raw)
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The differentiation of diastereomers by13C NMR spectroscopy
Magnetic Resonance in Chemistry, 1981
13C shifts are reported for diastereomers with halogen, oxygen and amino substituents which are mainly at vicinal chiral centres. The conformer populations underlying the 13C shift analysis can be verified by chemical means, such as change of temperature, solvent polarity (with dihalides), solvent hydrogen bonding capacity (with diols), deprotonation (with diacids) and by molecular mechanics calculations. The latter provide the basis for configurational and conformational assignments with a series of ephedrine derivatives. In accordance with the 13C shift observations, it is found that ephedrine derivatives predominate in conformations with a gauche O and N substituent arrangement, even in cases where hydrogen bonds are absent.
Tetrahedron, 1975
Abetract-Using an INDO approximation to Von Niessea's charge density localization method, the percent s character of the C atom hybrid orbitals engaged in C-H bonds is computed for a series of open-chain and cyclic saturated and unsaturated hydrocarbons. A semi-empirical linear relationship is found between these quantities and the experimental nuclear spin-spin coupling constants JCH (standard deviation 493 Hz). The experimental values of JCH were measured for quadricyclane (1) and tricyclo[3.1.0.6ulhexane (2) and were shown to be in fair agreement with the theoretical pred&ions. An analogous relationship is also established between the percent s charac-k of the involved C atom hybrid orbital and the C-H bond distance. the standard deviation beinn OM40 A. This relation is used in order to predict the diierent C-H bond lengths in the vibrational ground state of iand 2, for which equal CH distances were assumed in the analysis of electron diffraction experiments. The results indicate that molecular geometries can be retined with the use of semi-empirical correlations of the above mentioned type. lNrsloDlJmoN No accurate experimental molecular geometry has been reported hitherto for the highly strained molecules tetracyclo[3.2.0.a2'.O'~heptane (1) or quadricyclane and tricyclo[3.1 .O.@']hexane (2). 1 2 Kutchitsu et al.' described the results of a gas phase electron di&action experiment on quadricyclane. The experimental radial distribution curve was analysed with the help of several assumptions, one of them being that all C-H distances were equal. Assuming further either the r, (G-G) distance equal to that of cyclopropane (Method A), or r, (C&) equal to that of norbornane (Method B), the authors proposed two diierent sets of geometrical parameters. A similar procedure was followed by Geise et al.' in their electron diffraction investigations on tricyclo[3.l.O.~]hexane. Here too, several restrictions were imposed on the molecular geometry; once more, all C-H distances were set equal. In this paper, we will try to provide supplementary information on the nature of these C-H bonds with an experimental study of the JCH coupling constants and a theoretical investigation of these molecules using the *Author to whom inquiries should be addressed. tResearch candidates of the National Foundation for Scientific Research.
13C NMR spectra of polycyclic compounds and the stereochemistry of norbornadiene dimers and trimers
Bulletin of the Academy of Sciences of the USSR Division of Chemical Science, 1984
~3C NMR spectroscopy is widely used to establish the structure and stereochemistry of polycyclic hydrocarbons [1-3]o However literature data involving the study of the :~C NMR spectra of a broad class of dimers and trimers of bicyclo[2.2.1]hepta-2,5-diene(norbornadiene (NBD)) is essentially nonexistent. Meanwhile the compounds indicated have become firmly established in synthetic usage and it is evident that the scope of their usage will continue to grow.
ChemInform, 2010
H NMR spectra have been recorded for c(4)-hydroxy-r(2),c(6)-diphenylpiperidine 7a and its t(3)-methyl, t(3)-ethyl , t(3)-isopropyl, 3,3-dimethyl and t(3), t(5)-dimethyl derivatives 8a-12a and the corresponding axial 4-hydroxy epimers 7b-12b, at 270 MHz. Various 1 H chemical shifts and coupling constants have been determined by analysis of the spectra. The vicinal coupling constants suggest that boat form may make a slight contribution to the equatorial alcohols. The ~bea value for the 5-methylene protons is less in the axial alcohol than in the corresponding equatorial alcohol and in the case of lib this value is negative. The effects of methyl, ethyl, isopropyl and hydroxyl groups on the chemical shifts of ring protons are discussed. Analysis of the reported proton chemical shifts of 9-hydroxy-3,7-diazabicyclo[3 .3.l]nonanes la-4a suggests that the 3,7-diphenyl compounds should exist in boat-chair conformation.
A multinuclear NMR study of N-(chlorodimethylsilylmethyl) amides
Journal of Organometallic Chemistry, 1995
A series of N-(chlorodimethylsilylmethyl) amides of the type RCONR'(CH2Si(CH3)2CI), where R = H, R' = CH3; R = CH 3, R' = CH3; R = H, R' = C6H5; and R = CH3, R' =p-XC6H 4 (X = H, OCH3, El, Br, CF3, NO 2) were prepared by amination or transsilylation. The 1H, 13C, 14N, 170, anti 29Si NMR spectra were obtained and used to determine the structurc of the compounds. The laN and 170 shifts are indicative of the amide structure reported previously. The 170 and 29Si shifts can be related to the extent of dative interaction between the carbonyl oxygen and the silicon and correlate with the carbonyl stretching frequencies. The aH spectra of most of the acetanilides in CDCI 3 contain a broad peak for the Si(CH3) 2 protons. At lower temperatures this peak separates into two sharp peaks of unequal intensities. The two peaks can be attributed to rotamers, with the large peak at higher frequencies being due to the rotamer with the CH2Si(CH3)2C1 group cis to the carbonyl oxygen. In toluene, CH2C1 z and THF, the Si(CH3) 2 protons appear as a sharp peak which does not broaden upon heating to the boiling point of the solvent. The free energies of activation for rotation about the carbon-nitrogen bond were determined by the approximate method of Shanan-Atidi and Bar-Eli and show a rough correlation with the sigma constant of the substitucnt. * Corresponding authors. 0022-328X/95/$09.50 © 1995 Elsevier Science S.A. All rights reserved SSDI 0022-328X(94)05297-2 CHs ~, (, C H s fl Cl R/C~N~CH2
Journal of Physical Organic Chemistry, 2006
The complete assignment of the 1 H and 13 C NMR chemical shifts, from 2D techniques and spectra recorded at 500 MHz, for 3-substituted norbornanones with Cl, Br, I, SMe and SeMe substituents at endo and exo positions and 3-exo-hydroxynorbornanone is reported. The observed 1 H chemical shifts are compared with the corresponding calculated values using the semi-empirical CHARGE method and ab initio calculations at the B3LYP/ 6-311þþG(d,p) theory level. The molecular geometries were obtained through Density Functional Theory (DFT) methods. Good agreement between the experimental and both sets of calculated values is observed with the CHARGE calculations being more accurate for this series. This illustrates the utility of the CHARGE program for chemical shift assignments and also as a tool for the elucidation of chemical structures.