Decalin isomers

Examine the structures of trans and cis-decalin. What is the conformation of the two cyclohexane rings in each isomer Obtain the energy of each decalin isomer. Which is more stable and why ... 

Make a sketch of each decalin isomer, and label the orientation of the bridgehead hydrogens with respect to each ring (equatorial or axial). Build a plastic model of each isomer and determine its conformational flexibility (a flexible molecule can undergo a ring flip, but a locked molecule cannot). Is flexibility responsible for stabihty ... 

Appropriate choice of catalyst permitted formation of either of two dihydro derivatives of mevinolin in high yield (67). Hydrogenation of mevinolin over platinum oxide in ethyl acetate gave the tetrahydro derivative as a 1 3 mixture of CIS- and rrd 5-decalin isomers. 

Contrast between decalin isomers on the molecular structures of adsorption resulting in different dehydrogenation activities. 

Reported vapor pressures and Henry s law constants of decalin (isomer not specified) at various temperatures and the coefficients for the vapor pressure equations... 

Using what you know about the conformational energetics of substituted cyclohexanes, predict which of the two decalin isomers is more stable. Explain your reasoning. 

Our own interest in CyD modeling has evolved from the experimental study of molecular and chiral recognition of decalin isomers 1 by j8-CyD 2 [20, 8, 21]. These molecules provide a unique set for such studies since at room temperature the cis-isomer undergoes rapid ring inversions between the lb and Ic forms, which are enantiomers as well. Thus, decalin isomers allow us to study both molecular and chiral recognition. Chromatographic analysis by Sybilska s group [20] has shown that the trans isomer la forms weak complexes with 2 while the complexes with... 

As mentioned before, decalin isomers present an interesting case for analysis of the reliability of modeling of CyD complexation since they enable us to study molecular and chiral recognition for one set of isomeric guests. However, the lack of experimental data on the energy difference between the complexes involving the cis-decalin enantiomers prompted us to use another example to model chiral recognition, namely, the 1 2 complexes of enantiomers of a-pinenes 12 with a-CyD. 

Property Tetralin cis Decalin Mixed isomers trans... 

The decalin (bicyclo[4.4.0]decane) ring system provides another important system for study of conformational effects in cyclohexane rings. Equilibration of the cis and trans isomers reveals that the trans isomer is favored by about 2.8 kcal/mol. Note that this represents a change in configuration, not conformation. The energy difference can be analyzed by noting that the cis isomer has three more gauche butane interactions that are... 

There are probably several factors which contribute to determining the endo exo ratio in any specific case. These include steric effects, dipole-dipole interactions, and London dispersion forces. MO interpretations emphasize secondary orbital interactions between the It orbitals on the dienophile substituent(s) and the developing 7t bond between C-2 and C-3 of the diene. There are quite a few exceptions to the Alder rule, and in most cases the preference for the endo isomer is relatively modest. For example, whereas cyclopentadiene reacts with methyl acrylate in decalin solution to give mainly the endo adduct (75%), the ratio is solvent-sensitive and ranges up to 90% endo in methanol. When a methyl substituent is added to the dienophile (methyl methacrylate), the exo product predominates. ... 

Figure 4.17 Representations of cis- and frans-decalin. The red hydrogen atoms at the bridgehead carbons are on the same face of the rings in the cis isomer but on opposite faces in the trans isomer.

Problem 4.20 Which isomer is more stable, c/s-decalin or fram-decalin Explain. 

Thermolysis of the hexamethyl-substituted Dewar benzene-phenylazide adduct 1 in refluxing Decalin affords the 1.2,3-triazonine derivative 2 as the major product in form of a yellow-orange powder.30 A bicyelic isomer is also isolated which arises from rearrangement of 2 by purification on alumina and is readily converted back to 2 on heating to 80 C. 

In the course of studying the bromination reactions of the bicyclic systems we noticed that the reaction temperature has a dramatic influence on the product distribution. Increasing of the temperature gives non-rearranged reaction products (refs. 1,2). For this reason, we submitted 1 to high temperature bromination. To a solution of 1 in decalin at 150 C was added a hot solution of bromine in decalin in one portion. The colour of bromine disappeared immediately. After silica gel chromatography followed by fractional crystallization we isolated four products 2-6 in yields 8, 35, 37, and 9 % respectively. The structure of these compounds has been elucidated on the basis of spectral data by iH NMR and NMR experiments and by comparison with those reported in the literature. Symmetrical endo-c/5-isomer 6 has been observed for the first time. Studies concerning the mechanism of syn-addition show that the syn-adduct can arise either from direct... 

The isomerization observed in the methylenation of c/s-a-decalones has been turned to good advantage. Mixtures of cis- and tra/is-isomers of the a-decalones (44) and (46) gave only the /ra/i -decalins (45) and (47). 

A mixture of decalin (bicyclo[4.4.0]decane) isomers (Fluka, >98%) with a cis-to-trans ratio of 2-to-3 was used as a starting material. The experiments were performed in an electrically heated 300-mL stainless steel autoclave (Parr Industries) at 523 K and 2 MPa. The stirring rate and the starting material-to-catalyst ratio were kept at constant values equal to 1500 rpm and 22 (w/w), respectively. The screened catalysts were crushed and the fraction bellow 63 pm was used in the experiments to suppress internal diffusion. 

Furthermore, while no significant difference in the product distribution, with the exception of the trans-decalin/cis-decalin ratio, is observed for the tested proton-form zeolites, dissimilarity between Pt/H-Y on one hand and both Pt/H-Beta zeolites on the other hand is found (Figure 6). More ROP and CP, accompanied by less Iso, are formed on Pt/H-Y than on Pt/H-Beta zeolites. This implies that the consecutive ring opening and cracking are faster over Y-zeolite than over Beta-zeolites resulting in lower concentration of isomers and higher concentrations of ROP and CP. 

ROP. Their concentration is lower than the one of Ethyl- and Propyl-ROP at low conversions, but with increasing conversion they become the most abundant ROP group. Nevertheless, a noteworthy trend is observed for concentrations of all ROP groups, except Butyl-ROP, which increase rapidly after reaching conversion higher than 60%. This links the ROP formation to the secondary formed skeletal isomers of decalin (DMBCO) rather than to MBCN, which are present already at lower conversions in sufficient amounts. 

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