Trans-dimethyl cyclohexane

The most stable conformation of trans 1 4 dimethylcyclohexane has both methyl groups in equatorial orientations The two chair conformations of trans 1 4 dimethyl cyclohexane are not equivalent to each other One has two equatorial methyl groups the other two axial methyl groups... 

Both methyl groups are equatorial m the most stable conformation of trans 1 2 dimethyl cyclohexane... 

Two alkenes undergo hydrogenation to yield a mixture of as and trans 1 4 dimethyl cyclohexane A third however gives only as 1 4 dimethylcyclohexane What compound is this" ... 

The relative amounts of the two products however are not equal more as 1 2 dimethyl cyclohexane is formed than trans The reason for this is that it is the less hindered face of the double bond that approaches the catalyst surface and is the face to which hydro gen IS transferred Hydrogenation of 2 methyl(methylene)cyclohexane occurs preferen tially at the side of the double bond opposite that of the methyl group and leads to a faster rate of formation of the cis stereoisomer of the product... 

Cyclohexanedimethanol (47) starts from dimethyl terephthalate. The aromatic ring is hydrogenated in methanol to dimethyl cyclohexane-l,4-dicarboxylate (hexahydro-DMT) and the ester groups are further reduced under high pressure to the bis primary alcohol, usually as a 68/32 mixture of trans and cis forms. The mixed diol is a sticky low melting soHd, mp 45—50°C. It is of interest that waste PET polymer maybe direcdy hydrogenated in methanol to cyclohexanedimethanol (48). 

Obtain energies for diequatorial and diaxial conformers of cis-l,3-dimethylcyclohexane, trans-1,2-dimethyl-cyclohexane and trans-l,4-dimethylcyclohexane. 

Bei der Reduktion von tram- und m-(l,2-Dimethyl-cyclohexyl)-cyanamid mit Lithiumalanat werden iiberraschend als Hauptprodukte trans- bzw. cis-1 -Methylamino-1,2-dimethyl-cyclohexan gebildet3 ... 

Since the rate of opening of the two paths are equal, the enantiomorphs are formed in equal amount. Let us now take another interesting example of 1, 3 dimethyl cyclohexane. It exists in the cis and trans forms. Since the cis form has a plane of symmetry, it is the meso compound. 

When we considered trans- and c -1,2-dimethyl-cyclohexane, we found that only three configurational isomers exist, enantiomeric forms of the trans isomer, together with the cis isomer, which is an optically inactive meso compound (see Section 3.4.5). The meso relationship could be deduced from the plane of symmetry in the hexagon representation. 

Perfluoro- 1,3- dimethyl- cyclohexane Perfluoro- n-octane Perfluor- decaline (cis+trans Isomere) Perfluoro- perhydro- phenan- threne... 

The more stable chair—the one with both methyl groups equatorial—is the conformation adopted by most of the trans-1,4-dimethyl cyclohexane molecules. 

No. The major product cis- 1,2-dimethyl cyclohexane is less stable than the minor product trans-1,2-dimethylcyclohexane. 

Exercise 12-9 Draw the possible chair conformations of trans- and c/s-1,3-dimethyl-cyclohexane. Is the cis or the trans isomer likely to be the more stable Explain. 

Do not confuse this with cis and trans double bonds. There are no double bonds here. Don t draw any double bonds. It is amazing how many students will draw a double bond when you ask them to draw r/.v-l,2-dimethyl cyclohexane. Remember that the ending -ane- means that there are no double bonds anywhere in the molecule. The only comparison between double bonds and disubstituted cylohexanes is that, in both cases, cis means on the same side and trans means on opposite sides. ... 

Let s begin by considering a simple disubstituted cyclohexane, 1,2-dimethyl-cyclohexane. If the ring is drawn flat, in the plane of the page, then one substituent on each carbon projects above the page and the other projects below the page. The situation is somewhat similar to the cis-trans isomerism that occurs with alkenes. Both... 

Dimethyl- cyclohexan Solvent1) Temp. % cis % trans Overall yield [%]... 

In contrast to the m-enolizing 1,3-dicarbonyl compounds, the tran -enolizing cycloalkane-l,3-diones with four- to six-membered rings show exactly the opposite dependence on solvent polarity [46]. In these compounds, intramolecular hydrogen bonding is excluded on steric grounds. For example, 5,5-dimethyl cyclohexane-1,3-dione (5a,b) is 95% enolized in aqueous solution [51], However, in dilute solution in toluene, an apolar solvent, it is only 7% enolized [52, 134] x(enol) = 7 cmol/mol cf. Table 4-2. 

Trans-3-dimethyl- cyclohexane 8 7.99 Aliphl 0.05-0.12 Gasoline LUFT 1988... 

Conformational relationships for the three cis-trans pairs of dimethyl-cyclohexanes were examined by Beckett et al. (34). Here the situation becomes more involved than for methylcyclohexane because some of the isomers are dl pairs, each of which can exist as a pair of chair conformations. However, the conformational analysis of this system merits attention because it will provide a nearly complete basis for the conformational analysis of the deoalins, methyldecalins, and dimethyl-decalins in the following sections. 

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