Cyclohexane drawing chair conformation

Problem-Solving Strategy Drawing Chair Conformations 116 3-14 Conformations of Monosubstituted Cyclohexanes 117 3-15 Conformations of Disubstituted Cyclohexanes 120... 

You often will be asked to draw chair conformations of cyclohexane because these conformations allow you to identify which substituents are axial and which are equatorial. Although drawing chair conformations takes practice, following a few simple guidelines will make you an expert at drawing even complicated substitution patterns. 

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. 

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

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... 

SAMPLE SOLUTION (a) The most stable conformation is the one that has the larger substituent, the fe/t-butyl group, equatorial. Draw a chair conformation of cyclohexane, and place an equatorial tert-butyl group at one of its carbons. Add a methyl group at C-3 so that it is trans to the tert-butyl group. 

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. 

It molecule 19 is wntlen out in a zigzag fashion, the hydroxy groups at C-9 and C-l 1 arc seen to be treins to each other whereas those at C-3 and C-5 arc ris In the chair conformation oi the cyclohexane the two large substituents R of the C-3. C-5 acetal thus occupy equatorial positions (41). but this is not possible with the corresponding C-9, C-ll acetul 42. For this reason the latter is un likely to adopt a chair-like conformation. Even if these considerations represent only a first approximation, it is still possible to draw the correct conclusion, namely that the C-3.C 5 acetal 41 is thermodynamically favored, therefore leading to compound 43. 

In each of these problems, a tert-butyl group is the larger substituent and will be equatorial in the most stable conformation. Draw a chair conformation of cyclohexane, add an equatorial tert-butyl group, and then add the remaining substituent so as to give the required cis or trans relationship to the tert-butyl group. 

First write a chair conformation of cyclohexane, then add two methyl groups at C-1, and draw in the axial and equatorial bonds at C-3 and C-4. Next, add methyl groups to C-3 and C-4 so that they are cis to each other. There are two different ways that this can be accomplished either the C-3 and C-4 methyl groups are both up or they are both down. 

Draw the chair conformation of cyclohexane and show clearly the distinction between axial and equatorial bonds. 

In the space provided on the Report Sheet (2e), draw the structure of cyclohexane in the chair conformation with all 12 hydrogens attached. Label all the axial hydrogens, Ha, and all the equatorial hydrogens, He. How many hydrogens are labeled Ha (2f) How many hydrogens are labeled He (2g) ... 

Draw the two chair conformations of cyclohexane derivatives and determine which is more stable. (Problems 6.21, 6.22, and 6.25)... 

Draw the two chair conformations of each of the following substituted cyclohexanes. In each case, label the more stable conformation. 

Some students find it difficult to look at a chair conformation and tell whether a disubstituted cyclohexane is the cis isomer or the trans isomer. In the following drawing, the two methyl groups appear to be oriented in similar directions. They are actually trans but are often mistaken for cis. 

Let s consider whether cis-l, 2-dibromocyclohexane is chiral. If we did not know about chair conformations, we might draw a flat cyclohexane ring. With a flat ring, the molecule has an internal mirror plane of symmetry (cr), and it is achiral. 

Trying to draw the chair conformation of cyclohexane in one continuous line can lead to some dreadful diagrams. The easiest way to draw a chair conformation is by starting off with one end. 

The chair conformer of cis-1,4-disubstituted cyclohexane has one substituent equatorial, the other axial. This will not necessarily be the case for other substitution patterns for example, the chair conformer of a cis-1,3-disubs tituted cyclohexane has either both substituents axial or both equatorial. Remember, the raV and trans prefixes merely indicate that both groups are on the same side of the cyclohexane ring. Whether the substituents are both axial/equatorial or one axial and the other equatorial depends on the substitution pattern. Each time you meet a molecule, draw the conformation or make a model to find out which bonds are axial and equatorial. 

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... 

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