Planar cyclohexane ring

A planar cyclohexane ring would experience angle strain, because the internal bond angle between the carbon atoms would be 120°, and torsional strain, because aU of the hydrogens on adjacent carbon atoms would be eclipsed. 

IV. Molecules with a Planarized or Planar Cyclohexane Ring... 

IV, MOLECULES WITH A PLANARIZED OR PLANAR CYCLOHEXANE RING... 

According to MM calculations (37, 41a, 128) 13 is expected to possess planar cyclohexane rings thus it belongs also to the group discussed in the... 

An X-ray structure of 5yn-triepoxide (38) (74AG(E)539) shows that the cyclohexane ring is planar, with the three oxygens and sbt hydrogens lying in parallel planes 1.19 and 0.42 A respectively from the carbon plane. With all oxygens on one face , (38) forms a crystalline 2 1 complex with potassium iodide. 

The annulation of 4//-thiopyran and cyclohexane rings in 50a results in the planarity of the heterocycle and a half-chair conformation of the carbocycle (81KGS1342). On the other hand, a boat conformation of the 2//-thiopyran ring was found in the crystal of224b [91JCS(P2)2061], Other geometrical parameters were within the limits of the expected values (Fig. 2). 

Note that it is not necessary to consider both forms of cyciohexane, where the methyl is either wedged (up) or dotted (down). If the cyclohexane ring were planar, the two structures would be the same, since one merely has to turn the structure over to get the other. Although the cyclohexane ring is not planar, it turns out that the two structures are still identical, because of the ring flip process. This is shown below. One set of conformers is simply the upside-down version of the other. 

Now, although the cyclohexane ring is not planar, the overall consequences for trans- and cis-dimethylcyclohexane can be predicted by looking at the two-dimensional representations. 

Note that a cyclohexane system will be forced into a similar half-chair conformation by fusing a planar aromatic ring onto a cyclohexane ring (a tetrahydronaphthalene system). 

Similarly, cyclohexene will form 1,2-dibromo-cyclohexane as a racemic product, again R,R and S,S. Note that the three-membered ring of the bromonium ion must be planar and can only be defused to the cyclohexane ring (see Section 3.5.2). 

Conformational isomerism in cyclohexane Cyclohexane (C6H12) is a six-carbon cyclic alkane that occurs extensively in nature. Many pharmaceutically important compounds possess cyclohexane rings, e.g. steroidal molecules. If we consider cyclohexane as a planar and regular hexagon, the angles are 120° (cf. 109.5° for sp hybrids). 

P2i/c Z = 4 Dx = 1.392 R = 0.22 (all crystals were twinned) for 3,298 intensities. The structure determination was undertaken in order to establish the configuration. The cyclohexane ring is slightly distorted, owing to st/n-axial 0-2-0-4 interaction. The acetate groups are planar within 6°. 

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