Cyclohexanone hydrogen-bonding

The enthalpy of reaction 38 is ca 13 kJ mol" for the case of cyclohexanone wherein R R = —(CH2)5—. This difference is compatible with intermolecular hydrogen bonding as would be found for the benzoquinone oxime tautomer. In order to understand the energetics of reaction 39, we derived the solid phase enthalpy of formation of nitrosobenzene... 

Vibrational spectroscopy, too, has been used to study supercritical fluid systems. Buback reviewed (59) this area however, much of his discussions are on fluid systems that are well removed from ambient conditions or difficult to handle easily (e.g., H20, HC1). In an early report, Hyatt (21) used IR absorbance spectroscopy to determine the influence of several solvent systems, including COz, on the vibrational frequencies ( ) of solute molecules. Specifically, he studied the vc=o of acetone and cyclohexanone and vs.H of pyrrole. The goal of this work was to determine the suitability of supercritical fluids as reaction solvent. Hyatt concluded that the ketones experienced an environment similar to nonpolar hydrocarbons in COz and that there were no differences between liquid and supercritical CO2. In contrast, the pyrrole studies indicated that the solvent strength of CO2 was between ether and ethyl acetate. This apparent anomalous result was a manifestation of the, albeit weak, degree of pyrrole hydrogen bonding to CO2. 

A pyrrolidine-thiourea organocatalyst (69) facilitates Michael addition of cyclohexanone to both aryl and alkyl nitroalkenes with up to 98% de and ee 202 The bifunctional catalyst (69) can doubly hydrogen bond to the nitro group, leaving the chiral heterocycles positioned for cyclohexyl enamine formation over one face of the alkene. 

A variety of studies have been performed in which the chirality induced in ketone chromophores has been characterized by CD spectroscopy. CD has been induced in the n-+ r transition of cyclohexanone upon its dissolution into several alcoholic and ester-functionalized solvent systems [5]. In this work it was established that hydrogen bonding between solute and solvent was not required for the generation of solvent-induced CD. In a more comprehensive work, the CD induced in 20 compounds containing a ketone chromophore was studied in approximately 15 chiral solvent systems [6]. It proved difficult to develop general rules for the observation (or lack thereof) of solvent-induced CD, with the rotational strengths being found to be solvent, temperature, and... 

First the amino group was converted to a hydroxy group via a diazonium ion (Section 17.10). The benzene ring was reduced with hydrogen and a catalyst to produce cyclohexanol. Oxidation with potassium dichromate (Section 10.14) gave cyclohexanone. The bonds between the carbonyl carbon and both a-carbons were then cleaved by a series of reactions not covered in this book. The carbon of the carbonyl group was converted to carbon dioxide in this process. One-half of the original radioactivity was found in the carbon dioxide, and the other one-half was found in the other product, 1,5-pentanediamine. Additional experiments showed that the 14C in the diamine product was located at C-l or C-5. 

Consideration of the stabilizing interaction between the low-lying CT "-orbital associated with the bond forming between the incoming hydride and the carbonyl carbon, and remote electron-donor o-orbitals led Cieplak to an explanation for many kinetic and stereochemical effects in cyclohexanones that were previously unexplained. The normal preference for axial attack in simple cyclohexanones was attributed to the improved electron-donor ability of carbon-hydrogen bonds over carbon-carbon bonds that would be antiperiplanar to the incoming nucleophile in the transition state. 

The numerous reaction pathways found in Figure 32 invariably lead to an elimination of CO giving (CsHe) ion fragments (m/z 66). The PES can be divided into two distinct parts while the first part involves the three cyclohexanone ion isomers 22, 24 and 25, the second consists in the conversion of the cyclic keto-ions into either the various open-chain distonic forms 34 (or its conformers 35 and 36), 37 and 39, or the five-membered cyclic derivatives 29, 30 and 41. There are also some weak hydrogen bond complexes between CO and the CH bond of ionized cyclopentadienes such as 32 and 42. 

Brigghente IMC, Vottero LR, Terenzani A, Yunes RA (1991) Addition of hydroxylamine to cyclohexanone and bicyclic ketones. Steric, electronic and hydrogen bonding effects on the general mechanism of addition of amines to carbonyl compounds. J Phys Org Chem 4 107... 

The lower selectivity of PtHFAU catalysts is due to the very rapid formation of Ce cyclic hydrocarbons (family 1). The same trend has been found in the case of acetone transformation [3]. This can be explained by the lower activity of the palladium relatively to the platinum to hydrogenate the C=0 bond. This lower activity which has been found in the case of cyclohexanone hydrogenation on platinum group metals was explained by a weaker adsorption of the ketone on Pd in comparison with Pt and Ru [9]. 

Aaron et al. have studied the intramolecular hydrogen bonding in hy-droxypyrrolizidines.89 They found that with 1-hydroxypyrrolizidines, IR spectra did not positively indicate any hydrogen bonding. On the other hand, with 2-hydroxypyrrolizidines, the cis-epimer (128) is readily isomerized (cyclohexanone, CSH j OK/CsH j,OH) to the more stable trans-epimer (129), which has a relatively weak intramolecular hydrogen bond, displaying a frequency shift of 35 cm"1 [Eq. (34)]. 

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