Cyclohexane chair, drawing

Practice drawing cyclohexane chairs oriented in either direction... 

Pr actice drawing cyclohexane chair s oriented in either dir ection. 

Fig. 7.1 Symbolic drawings of cyclohexane chair and boat conformations in two dimensions using different line thickness and wedge symbols.

Note that the wedges and bold bonds help to show how we are looking at the cyclohexane chair. In practice, particularly to speed up the drawing of structures, we tend to omit these. Then, by convention, the lower bonds... 

The cyclohexane chair just drawn has the headrest to the left and the footrest to the right. Draw a cyclohexane chair with its axial and equatorial bonds, having the headrest to the right and the footrest to the left. 

It would seem that this uncommon behaviour of a six-membered ring is due to the two pairs of sulphur atoms long sulphur-sulphur and sulphur-carbon bonds make the interactions in a chair conformation very different from those of the cyclohexane chair, so that it would be dangerous to draw conclusions for cyclohexane on the basis of 35 and 36. 

Name an Alkane Using the lUPAC System 122 Name a Cycloalkane Using the lUPAC System 126 Draw a Newman Projection 132 Draw the Chair Form of Cyclohexane 140 Draw the Two Conformations for a Substituted Cyclohexane 143 Draw Two Conformations for a Disubstimted Cyclohexane 146 Stereochemistry... 

In drawing the cyclohexane chair, keep in mind that there are four carbons in a plane. On one end there is a carbon oriented above the plane and on the other end there is a carbon oriented below the plane. Each carbon has an equatorial hydrogen oriented along the perimeter. There are three axial hydrogens on alternating carbons above the ring and three on the other carbons below the ring. 

To understand cis and trans on the cyclohexane chair, first draw the chair and insert bonds for the axial and equatorial positions (these are labeled in the diagram). Then note on each carbon, one bond can be considered up (u) and one down (d) relative to one another. In disubstituted cyclohexanes, if both groups are up or both down the isomer is cis. If they are up/down or down/up, the isomer is trans. Rationalize this with the chart in the textbook Problem 2.36. For example,in 1,2-disubstituted cyclohexanes, up/up or down/down is ax/eq or eq/ax and up/down or down/up is ax/ax or eq/eq. 

Flexibility. Many rings are highly mobile. One example of this phenomenon is the ring flip of cyclohexane. You must be able to flip cyclohexanes and draw the two interconverting chair forms well. 

Being able to draw cyclohexane chair conformations will help you learn the chemistry of six-membered rings. Several rules are useful. 

Bromoalcohol A transforms rapidly in the presence of sodium hydroxide to give the corresponding oxacyclopropane, whereas its diastereomer B does not. Why [Caution Unlike the previous problem, both substrates are frans-bromoalcohols. Hint Draw the most stable cyclohexane chair conformers of both isomers (Section 4-4) and picture the respective transition states for the intramolecular Williamson ether synthesis.]... 

To convert a Haworth projection into a 3-D representation with a chair cyclohexane [ 1 ] Draw the pyranose ring as a chair with the O as an up atom. 

The conformational features of six membered rings are fundamental to organic chemistry so it is essential that you have a clear understanding of the directional prop erties of axial and equatorial bonds and be able to represent them accurately Figure 3 17 offers some guidance on the drawing of chair cyclohexane rings... 

It IS no accident that sections of our chair cyclohexane drawings resemble saw horse projections of staggered conformations of alkanes The same spatial relationships seen m alkanes carry over to substituents on a six membered ring In the structure... 

The easiest way to visualize chair cyclohexane is to build a molecular model. (In fact do it now.) Two-dimensional drawings like that in Figure 4.7 are useful, but there s no substitute for holding, twisting, and turning a three-dimensional model in your own hands. The chair conformation of cyclohexane can be drawn in three steps. 

Figure 4.10 A procedure for drawing axial and equatorial bonds in chair cyclohexane.

Amantadine is an antiviral agent that is active against influenza A infection and against some strains of H5NX avian flu. Draw a three-dimensional representation of amantadine showing the chair cyclohexane rings. 

An interesting case of conformational analysis comes to play when we consider a six-membered ring (cyclohexane). There are many conformations that this compound can adopt. You will see them all in your textbook the chair, the boat, the twist-boat. The most stable conformation of cyclohexane is the chair. We call it a chair, because when you draw it, it looks like a chair ... 

EXERCISE 6.30 Below you will see one chair conformation of a substituted cyclohexane. Draw the other chair (i.e., do a ring flip) ... 

Fig. 18. Top transition coordinates (with symmetry species) of conformational transition states of cyclohexane (top and side views). Hydrogen displacements are omitted. The displacement amplitudes given are towards the C2v-symmetric boat form, and towards >2-symmetric twist forms (from left), respectively. Inversion of these displacements leads to the chair and an equivalent T>2-form, respectively. Displacements of obscured atoms are given as open arrows, obscured displacements as an additional top. See Fig. 17 for perspective conformational drawings. Bottom pseudorotational normal coordinates (with symmetry species) of the Cs- and C2-symmetric transition states. The phases of the displacement amplitudes are chosen such that a mutual interconversion of both forms results. The two conformations are viewed down the CC-bonds around which the ring torsion angles - 7.3 and - 13.1° are calculated (Fig. 17). The displacement components perpendicular to the drawing plane are comparatively small. - See text for further details.

Figure 4.12 Representations of the chair conformation of cyclohexane (a) Carbon skeleton only (b) Carbon and hydrogen atoms (c) Line drawing (d) Space-filling model of cyclohexane. Notice that there are two types of hydrogen substituents—those that project obviously up or down (shown in red) and those that lie around the perimeter of the ring in more subtle up or down orientations (shown in black or gray). We shall discuss this further in Section 4.13.

You can only appreciate stereochemical features if you can draw a representation that correctly pictures the molecule. One of the most challenging is the chair conformation of cyclohexane. Practice makes perfect so this is how it is done. 

We saw early in Section 3.3.2 that, if we draw cyclohexane in typical two-dimensional form, the bonds to the ring could be described as up or down , according to whether they are wedged or dotted. This is how we would see the molecule if we viewed it from the top. When we look at the molecule from the side, we now see the chair conformation the ring is not planar as the two-dimensional form suggests. Bonds still maintain their up and down relationship, but this means bonds shown as up alternate axial-equatorial around the ring they are... 

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