Hydrogen conformational analysis

Stereochemistry and Mechanism of Hydrogenation of Naphthalenes on Transition Metal Catalysts and Conformational Analysis of the Products A. W. Weitkamp... 

IR spectra of thiolane oxides in the solid phase were shown to be most outstandingly different in the sulfoxide region depending on the particular crystalline state/structure a fact which can be used to advantage for conformational analysis. Also, as one could expect, the sulfoxide absorptions indicate strong hydrogen bonding. 

Combined dipole moment and Kerr effect studies are regularly used by Russian workers for the conformational analysis of phosphorus heterocyc1es.135 230 In a study of the interaction of phenol with phosphoryl groups the Kerr effect was used to evaluate not only the extent of hydrogen bonding but also the influence of changes in polarity and polarisation upon stability constants.231 In a similar study the orientation of the aryl groups of 1,3,5-triazaphosphorines (82) were shown to be less coplanar than biphenyl in the gas phase. 2 3 2... 

Teppen, B. J., M. Cao, R. F. Frey, C. Van Alsenoy, D. M. Miller, and L. Schafer. 1994a. An Investigation into Intramolecular Hydrogen Bonding Impact of Basis Set and Electron Correlation on the Ab Initio Conformational Analysis of 1,2-Ethanediol and 1,2,3-Propanetriol. J. Mol. Struct. (Theochem) 314,169-190. 

Weitkamp, A.W., Stereochemistry and mechanism of hydrogenation of naphthalene on transition metal catalysts and conformational analysis of the products. Adv. Catal., 18,1-110 (1968). 

C. J. Cramer and D. G. Truhlar, Quantum chemical conformational analysis of 1,2-ethanediol Correlation and solvation effects on the tendency to form internal hydrogen bonds in the gas phase and aqueous solution, J. Am. Chem. Soc. 116 3892 (1994). 

Aaron, Herbert S., Conformational Analysis of Intramolecular-Hydrogen-Bonded Compounds in Dilute Solution by Infrared Spectroscopy, 11, 1. 

One example of the use of 2D-NMR experiments in conformational analysis is the study of molecular interactions between cinchonidine and acetic acid [26]. These alkaloids are used as chiral auxiliaries in enantioselective hydrogenations, and the enantiomeric excess is dependent on solvent polarity, acetic acid being a good solvent This suggests that protonation and a preferred conformation play a role in achieving high enantioselectivities. With a combination of COSY-experiments, 3J coupling constants and NOESY experiments, it was shown that one conformer is preferred in acidic solutions. 

The configuration of the product in diastereoselective hydrogenation -whether 1,2-syn or 1,2-anti - is related to the substitution pattern of the starting alkene. The allyl alcohol with a 1,1-disubstituted olefin unit affords the antiproduct, while the syn-product is formed from the allyl alcohol with a trisubsti-tuted olefmic bond (Table 21.8, entries 6-9). The complementarity in diastereoselective hydrogenation of di- and tri-substituted olefins may be rationalized based on the conformation analysis of the intermediary complex (Scheme 21.1)... 

The accurate spatial location of these atoms generally needs a sophisticated approach, for example, the study of a complete deuterated set of isotopic derivatives in microwave spectroscopy or the use of neutron diffraction techniques. We shall see below that a set of CNDO/2 calculations combined with suitable experiments (microwave spectroscopy and/or electron diffraction) may help to solve the geometrical and conformational analysis of compounds containing many hydrogen atoms. 

A study of the vibrational spectra and force field of this molecule in dilute solution showed that this preferred conformation could not be transposed to the liquid state because there exist in solution some (F. .. H) hydrogen bonding interactions which, not being affected by dilution, must consequently have an intramolecular character. Such (F. .. H) interactions cannot be understood from the solid-state preferred conformation so that we had to reexamine the conformational analysis of (CH3)2SO BF3. 

The torsion angles predicted by conformational analysis agree closely with those of crystalline cellobiose as measured by X-ray diffraction, the conformation of which is restricted by two chain-stabilising intramolecular hydrogen bonds between 0(3 )-H and 0(5) and also between 0(2 )-H and 0(6) (Figure 4.3). These are also found in cellulose and they assist in maintaining the highly extended conformation which allows it to function as a structural polymer. 

Two of the worst outliers were N,N-dimethylformamide and N,N-dimethyl-acetamide. For both of these, solubility in water was greatly underestimated. This may illustrate a situation in which conformation does assume importance. In the gas phase structures used to compute the surface properties, the nitrogens are planar. There is reason to believe, however, that interaction with water molecules will cause the nitrogens to become pyramidal,48 since that produces more localized lone pairs that better attract water hydrogens. Thus, analysis involving planar nitrogens would not indicate the true strength of the interaction. 

Tight turns were first recognized from a theoretical conformational analysis by Venkatachalam (1968). He considered what conformations were available to a system of three linked peptide units (or four successive residues) that could be stabilized by a backbone hydrogen bond between the CO of residue n and the NH of residue n + 3. He... 

Barton and 0. Hassel (Barton, Hassel) Conformational Analysis of Intramolecular Hydrogen-Bonded Com- 6 1... 

Hydrogen-Bonded Compounds, Intramolecular, in Dilute Solution, Conformational Analysis of, by Infrared Spectroscopy (Aaron). . . 11 1... 

Hadler 26) employed conformational analysis to explain the difference in the proportion of cholestane to coprostane derivatives resulting from the reduction of A and d steroids. He suggested that the hydrogenation process involved the formation of a quasi-ring structure between the unsaturated carbon atoms and two hydrogens originally dissolved in the metal, a mechanism which is similar to one proposed by Beeck (27) and by Jenkins and Rideal 28). He assumed, in effect, that the saturated struc-... 

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