Methylcyclohexane, 1,3-diaxial interactions

Methyl-3-buten-l-ol, NMR spectrum of, 647 Methylcyclohexane, 1,3-diaxial interactions in, 123 conformations of, 123 mass spectrum of, 4H molecular model of, 123, 293... 

Figure 4.14 The origin of 1,3-diaxial interactions in methylcyclohexane. The steric strain between an axial methyl group and an axial hydrogen atom three carbons away is identical to the steric strain in gauche butane. Note that the -CH3 group in methylcyclohexane moves slightly away from a true axial position to minimize the strain.

Figure 4.20 (a) The conformations of methylcyclohexane with the methyl group axial (1) and and equatorial (2). (b) 1,3-Diaxial interactions between... 

We saw in Problem 4.20 that c/.s-decalin is less stable than fm/rs-decalin. Assume that the l/t-diaxial interactions in frnn.s-decaiin are simiiai to those in axial methylcyclohexane [that is, one Cl h —>11 interaction costs 3.8 kj/rnol (0.9 kcal/mol), and calculate the magnitude of the energv difference between d.s- and /wns-decalin. 

As a simple example of the importance of 1,3-diaxial interactions, let us consider methylcyclohexane. In estimating relative stabilities of various conformations of this compound, we must focus our attention on methyl, since it is the largest substituent on the ring and hence the one most subject to crowding. There are two... 

Figure 9.10. 1,3-Diaxial interaction in methylcyclohexane. Axial —CH3 more crowded than equatorial —CH3.

One of the two chair structures of cis-l-chloro-3-methylcyclohexane is more stable than the other by 15.5 kJ/mol (3.7 kcal/mol). Which is it What is the energy cost of a 1,3-diaxial interaction between a chlorine and a methyl group ... 

Assume that the 1,3-diaxial interactions in tn / .s-decalin are similar to those in axial methylcyclohexane [that is, one interaction costs 3.8 kj/mol... 

The strain caused by a 1,3-diaxial interaction in methylcyclohexane is the same as the strain caused by the close proximity of the hydrogen atoms of methyl groups in the gauche form of butane (Section 4.9). Recall that the interaction m gauche-h xtda t (called. 

Consider methylcyclohexane (Figure 2.21). When —CHj is axial, it is parallel to the axial C—H bonds on carbons 3 and 5. Thus, for axial methylcyclohexane, there are two unfavorable methyl-hydrogen diaxial interactions. No such unfavorable interactions exist when the methyl group is in an equatorial position. For methylcyclohexane, the equatorial methyl conformation is favored over the axial methyl conformation by approximately 7.28 kj (1.74 kcal)/mol. 

Two chair conformations of methylcyclohexane.The steric strain introduced by two diaxial interactions makes the axial methyl conformation less stable by approximately 7.28 kj (1.74 kcal)/mol. 

A gauche conformer of butane and the axially substituted conformer of methylcyclohexane are compared in Figure 3.15. Notice that the gauche interaction in butane is the same as a 1,3-diaxial interaction in methylcyclohexane. 

Butane has one gauche interaction between a methyl group and a hydrogen, whereas methylcyclohexane has two 1,3-diaxial interactions between a methyl group and a hydrogen. 

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