Cyclohexanol conformation

Morpholinosulfur trifluoride is more thermally stable and therefore safer to handle than DAST and gives a slightly higher yield of the fluoride in the fluorination of cyclohexanol [95, ISO] Both solvent and conformational effects are pronounced in the fluorination of cyclohexanols [550] The chiral (S)-2-(methoxymethyl)pyr-rolidin-l-ylsulfur tnfluonde is an effective enantioselective fluorodehydroxylating agent [ISI]... 

Draw two different chair conformations of cyclohexanol (hvdroxycvclohexane), showing all hydrogen atoms. Identify each position as axial or equatorial. 

What is the energy difference between the axial and equatorial conformations of cyclohexanol (hydroxycyclohexanel ... 

The 1H NMR spectra of the epimeric cyclohexanols in DMSO reveal that the hydroxyl proton in the axial alcohol shows a resonance absorption at a higher field than in the equatorial one, indicating that the conformational effect of the hydrogen bond influences the XH NMR chemical shifts128. 

TFe data of Popov et alm for Ag contradict the above sequence. They found that pentanol adsorbed more strongly on Ag(100) than on Ag(l 11). Similarly, Cd(0001) adsorbs less strongly than pc-Cd.661 The data for Sb and Bi are to some extent contradictory since the trend is broadly correct but with scatter, which is attributed to the crystal face specificity of space-charge effects.153 For instance, adsorption of cyclohexanol on Bi conforms to the sequence (011) > (101) > (211) > (001) >(111), while the capacitance at a - Ovaries in the sequence (001) > (011) > (211) > (101) > (111). Thus only the faces (001), (211), and (111) are in the expected order. Surprisingly, the Cd data of Lust etal. show similarities with those of Naneva etal.,212 although capacitances disagree. Thus the order of cyclohexanol adsorbability is (1010) > (0001) while the capacitance varies in the order (1010) > (1120) > (0001), i.e., the other way round. In these cases one might wonder whether the G(M-B) term is really independent of face. 

A single electron avoids the problem of forcing multiple charges into close proximity Shkrob and Schlueter have calculated that the cavity of one conformation of calix[4]cyclohexanol, a cyclic tetramer of 2-methylcyclohexanol, represents a deep electron trap. Essentially, the electron would be solvated by four hydroxy groups in a tetrahedral arrangement. Such a molecule could serve as a nanocapacitor for a unit charge [132]. 

Depending on the orientation of substituents, the disubstituted cyclohexanes can be either equatorial-axial or diequatorial. This is illustrated with 2-methyl cyclohexanol. It exists in two stereoisomeric forms and each of which has two conformations which are readily interconvertible. 

For the a-SCS(OH) values in cyclohexanol derivatives Wray (406) has suggested that a further parameter is necessary to account for four-bond interactions, as indicated in 298 and 299. He remarked that significant deviations from the experimental chemical shifts indicate conformational distortion of the parent compound, and that such SCS values cannot be calculated for five-membered ring alcohols (406). 

The conformational equilibria of various methylated cyclohexanols have been... 

Kinetic studies of hexacyanoferrate(III) oxidations have included the much-studied reaction with iodide and oxidation of the TICI2 anion, of hydrazine and hydrazinium, and of phenylhydrazine and 4-bromophenylhydrazine. These last reactions proceed by outer-sphere mechanisms, and conform to Marcus s theory. Catalyzed [Fe(CN)g] oxidations have included chlororuthenium-catalyzed oxidation of cyclohexanol, ruthenium(III)-catalyzed oxidation of 2-aminoethanol and of 3-aminopropanol, ruthenium(VI)-catalyzed oxidation of lactate, tartrate, and glycolate, and osmium(VIII)-catalyzed oxidation of benzyl alcohol and benzylamine. ... 

The cyclizations of cis- and lrans-2-hydroxymethyl-l-cyclohexylamine and cis- and lram-2-aminomethyl-l-cyclohexanol with 4-nitrobenzaldehyde have been studied by means of H NMR spectroscopy in CDCI3 solution (90ACSA364 91T2229). The time-dependent spectra confirmed that the reactions of all these amino alcohols proceeded via Schiff bases. With the exception of cis-2-hydroxymethyl-l-cyclohexylamine, the thermodynamically more stable perhydrobenzoxazine epimer is also the kinetically favored product. In the former case, from amino alcohol 21 (R = H), the Schiff base 37 with N-outside predominant conformation is formed first due to kinetic control, the less stable epimeric ring form 38 is obtained with N-outside predominant conformation. The thermodynamically controlled product 33 is formed subsequently, via the less stable open-chain form 37, in a slow equilibration process (90ACSA364). 

By choosing an appropriate titanium complex, a /ra r-isomer of 1,2-cyclohexanols can be prepared selectively. Because intramolecular pinacol coupling of hexanedials with Sml2 usually produces t-isomers of cyclohexane-1,2-diols, the titanium-mediated reaction complements the samarium-mediated cyclization (Equation (17)). In addition, when a /-butyl group fixes the conformation of the substrate, one of the diastereomers is produced selectively (Equation (18)). ... 

Cycloalkanes can be oxygenated when irradiated in the presence of nitrobenzene.196 A 50% yield of cyclohexanol and cyclohexanone is achieved from cyclohexane. Since the product ratio is independent of reaction time, the alcohol is not an intermediate in ketone formation. Isomeric 1,2-dimethylcyclohexanes give an identical mixture of the isomeric tertiary alcohols, indicative of conformational equilibration and the presence of a radical intermediate. 

Small molecules may also form condis crystals, provided they posses suitable conformational isomers, It is of interest to note that several of the organic molecules normally identified as plastic crystals are probably better described as condis crystals. Their motion was, as already shown in Sect. 5.2.2, not the complete reorientation of the presumed rigid molecule, but rather an exchange between a limited number of conformational isomers. The examples treated in Sect. 5.2.2 are 2,3-dimethyl-butane, cyclohexanol and cyclohexane. 

The first tiiree types of isomerism are familiar and have been discussed previously. The conformational isomerism is very understandable if it is remembered tiiat axial and equatorial valences exchange upon chair-chair interconversion. For example, to draw die trans isomer of 3-metiiylcyclohexanol, one of the groups must be equatorial and die otiier axial. The otiier chair form must have die groups in opposite valences. Similarly frans-2-metiiyl-cyclohexanol has both groups equatorial in one chair form. The otiier chair form must therefore have both groups axial. 

Steric effects also play a significant role, as is apparent in the monosubstituted cyclohexanols series (entries 7-9 in Table 13.3) and from comparison between linear and branched substrates (entry 1 vs. entry 3). This effect is so strong that in disubstituted cyclohexanols the reaction takes place at reasonable rates only when the —OH group is in axial conformation, as shown by the comparison of (-)-menthol (entry 16) and neomenthol (entry 17). This particular behavior could once more be exploited for synthetic purposes, in order to set up a kinetic resolution process. This has indeed been achieved in the one-pot hydrogenation of pennyroyal oil into menthol [67]. 

The positions of the equilibria between the di-equatorial and di-axial conformers of trans-1,2-dimethoxycyclohexane and trans-2-methoxy-cyclohexanol were determined accurately by 13C NMR spectroscopy at —80 °C using a number of solvents ranging from non-polar pentane to the strongly polar methanol (cf. Table IV) (96AJC379). The di-equatorial conformer is preferred under all conditions but the extent increases... 

As for inter molecular substitutions, the incoming nucleophile must still attack into the a orbital of the leaving group. In the formation of an epoxide, such an attack can take place only if both groups are axially substituted. As a consequence, only a trans 2-chloro cyclohexanol can form an epoxide, and then only when in the less energetically favourable conformation with both groups axial, Of course, as the diaxial conformer reacts, rapid ring inversion of the major equatorial isomer ensures that it is replaced. 

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