4-Methylcyclohexene

Alcohol dehydration is an acid-catalyzed reaction performed by strong, concentrated mineral acids such as sulfuric and phosphoric acids. The acid protonates the alcoholic hydroxyl group, permitting it to dissociate as water. Loss of a proton from the intermediate (elimination) brings about an alkene. Because sulfuric acid often causes extensive charring in this reaction, phosphoric acid, which is comparatively free of this problem, is a better choice. To make the reaction proceed faster, however, a minimal amount of sulfuric acid will also be used. 

The equilibrium that attends this reaction will be shifted in favor of the product by distilling it from the reaction mixture as it is formed. The 4-methylcyclohexene (bp 101-102°C) will codistill with the water that is also formed. By continuously removing the products, one can obtain a high yield of 4-methylcyclohexene. Because the starting material, 4-methylcyclohexanol, also has a somewhat low boiling point (bp 171-173°C), the distillation must be done carefully so that the alcohol does not also distill. 

Unavoidably, a small amount of phosphoric acid codistills with the product. It is removed by washing the distillate mixture with a saturated sodium chloride solution. This step also partially removes the water from the 4-methylcyclohexene layer the drying process will be completed by allowing the product to stand over anhydrous sodium sulfate. 

Compounds containing double bonds react with a bromine solution (red) to decolorize it. Similarly, they react with a solution of potassium permanganate (purple) to discharge its color and produce a brown precipitate (MnOj). These reactions are often used as qualitative tests to determine the presence of a double bond in an organic molecule (see Experiment 53). Both tests will be performed on the 4-meth-ylcyclohexene formed in this experiment. 

If performing the optional boiling point or infrared spectroscopy, also read  

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As a second example consider the regioselective dehydration of 2 methylcyclo hexanol to yield a mixture of 1 methylcyclohexene (major) and 3 methylcyclohexene (minor)... 

The reaction course taken by photoexcited cycloalkenes in hydroxylic solvents depends on ring size. 1-Methylcyclohexene, 1-methylcycloheptene, and 1-methylcyclooc-tene all add methanol, but neither 1-methylcyclopentene nor norbomene does so. The key intermediate in the addition reactions is believed to be the highly reactive -isomer of the cycloalkene. 

Cyclic perfluoroalkenes are oxidized to the corresponding epoxides in high yields by sodium hypochlorite in aqueous acetonitrile at 0-20 C [13, 75J (equations 9 and 10) Perfluorocycloheptene gives the epoxide after 1 h in 85% yield [17] Epoxidation of perfluoro-1-methylcyclohexene is accomplished with... 

The rate of transfer hydrogenation also varies markedly with donor structure. For cyclohexene, 1 -methylcyclohexene, l-methyl-4-isopropyl-cyclohexene,and l-methyl-4-f-butyIcycIohexene as donor in the above hydrogenations, after 1 min the reduction was 11, 78, 99, and 99% complete, respectively (97). 

For example, addition of H+ to 2-methylpropene yields the intermediate terticuy carbocation rather than the alternative primary carbocation, and addition to 1-methylcyclohexene yields a tertiary cation rather than a secondary one. Why should this be ... 

Dehydration is often carried out by treatment of an alcohol with a strong acid. For example, loss of water occurs and 1-methylcyclohexene is formed... 

Treatment of an alkyl halide with a strong base such as KOH yields an. alkene. To find the products in a specific case, locate the hydrogen atoms on each carbon next to the leaving group. Then generate the potential alkene products by removing HX in as many ways as possible. The major product will be the one that has the most highly substituted double bond—in tints case, 1-methylcyclohexene. 

Methylcyclohexene will have five sp3-carbon resonances in the 20 to 50 6 range and two s/ -carbon resonances in the 100 to 150 6 range. Methylenecyclohexane, however, because of its symmetry, will have only three sp3-carbon... 

Figure 13.11 The 13C NMR spectrum of 1-methylcyclohexene, the E2 reaction product from treatment of 1-chloro-1-methylcyclohexane with base.

As noted at the end of Section 7.8, the prefixes cis- and trans- would be ambiguous when naming the diols derived from 1-methylcyclohexene because the ring has three substituents. Instead, a reference substituent r is chosen and other substituents are either cis (c) or trans (f) to that reference. For the two l-methyl-l,2-cyc ohexanediol isomers, the -OH group at Cl is the reference (r-1), and the -OH at C2 is either cis (c-2) or trans (t-2) to that reference. Thus, the diol isomer derived by cis hydroxylation is named l-methyl-r-l,c-2-cyc ohexanediol, and the isomer derived by trans hydroxylation is named l-methyl-r-l,t-2-cyclohexanediol. 

Problem 19.4 How would you carry out the following reactions More than one step may be required, (a) 3-Hexvne 3-Hexanone, (b) Benzene —> m-Bromoacetophenone I (c) Bromobenzene —> Acetophenone (d) 1-Methylcyclohexene — 2-Methylcyclohexanone... 

Gas chromatographic analysis, using an HMDS-treated Chromo-sorb W column with 7% Craig polyester as the stationary phase, indicated the product to have a purity of 97%. The 3% impurity is most probably the isomeric 1-methylcyclohexene. 

Ion 21 can either lose a proton or combine with chloride ion. If it loses a proton, the product is an unsaturated ketone the mechanism is similar to the tetrahedral mechanism of Chapter 10, but with the charges reversed. If it combines with chloride, the product is a 3-halo ketone, which can be isolated, so that the result is addition to the double bond (see 15-45). On the other hand, the p-halo ketone may, under the conditions of the reaction, lose HCl to give the unsaturated ketone, this time by an addition-elimination mechanism. In the case of unsymmetrical alkenes, the attacking ion prefers the position at which there are more hydrogens, following Markovnikov s rule (p. 984). Anhydrides and carboxylic acids (the latter with a proton acid such as anhydrous HF, H2SO4, or polyphosphoric acid as a catalyst) are sometimes used instead of acyl halides. With some substrates and catalysts double-bond migrations are occasionally encountered so that, for example, when 1 -methylcyclohexene was acylated with acetic anhydride and zinc chloride, the major product was 6-acetyl-1-methylcyclohexene. ... 

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