Cyclohexane drawing chair form

Draw the three-dimensional structures of the following, indicating the interactions that may exist (a) -butane in its staggered form (b) -butane in its eclipsed form about the 2,3-bond (c) 1,2-dibromoethane in its most stable form (d) cyclopropane (e) 1,2-epoxyethane (ethylene oxide) showing the lone pairs of electrons on the oxygen (f) cis- and rart.v-1,4-dimethylcyclohexane in the chair form (g) /ran.v-cyclohexane-l,2-dicarboxylic acid (h) cyclohexene. 

A three-dimensional representation of the chair form is drawn in Figure 4.12. Before continuing, we must first learn how to draw the chair form of cyclohexane. 

Remember In determining chirality in substituted cycloalkanes, always draw the rings as flat polygons. This is especially true for cyclohexane derivatives, where having two chair forms that interconvert can make analysis especially difficult. 

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... 

The first concept that needs to be introduced here is the half-chair. Assuming you know how to draw the chair form of a cyclohexane, then the half-chair is a way to describe cyclohexene. One half of the normal chair has been flattened - hence the term half-chair . 

Draw skeletal structures of the boat and chair forms of cyclohexane. 

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. 

PROBLEM 5.52 Draw both chair forms for the following cyclohexanes. Indicate the more stable chair form in each case. Not all examples will be obvious some choices may be too close to call. 

HOWTO Draw the Chair Form of Cyclohexane Step [1] Draw the carbon skeleton. 

The cyclitols are a group of carbocyclic sugar derivatives having the general formulation cyclohexane-1,2,3,4,5,6-hexol. How many stereo-isomeric cychtols are possible Draw them in their chair forms. 

The structure on the far left, of course, does not imply any three-dimensional geometry, and certainly a chemist would know that this is not a planar molecule. The middle and right structures do try to show the structure of this molecule in three dimensions. This particular conformation is known as the "chair" form of cyclohexane. Perhaps the "chair" reference can be seen in the structure on the right Hopefully, readers of this book who are not familiar with chemical drawings have learned enough in these few pages to appreciate the complexity of the molecules shown, and visualize the mirror-image relationships of chiral centers. 

The bond angles are approximately 109.5° in both the chair and the boat forms of cyclohexane. However, the chair form of cyclohexane is slightly lower in energy. Why is this To answer this question, we will first describe how to draw the chair form of cyclohexane and then use a Newman projection to provide the insight needed. 

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.

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... 

As was indicated in Table 3.6 (p. 95), cyclodecane is significantly more strained than cyclohexane. Examination of the boat-chair-boat conformation reveals that the source of most of this strain is the close van der Waals contacts between two sets of three hydrogens on either side of the molecule. The hydrogens involved are shown in the drawing. Distortion of the molecule to twist forms to relieve this interaction introduces torsional strain. It seems reasonable to assume that suitably substituted cyclodecanes may be found in which the transannular van der Waials repulsion is sufficiently large to allow a conformation other than the boat-chair-boat to be the most stable. 

Draw the alternative chair conformations for the product formed by the addition of bromine to 4-tert-butylcyclohexene.The Gibbs free energy differences between equatorial and axial substituents on a cyclohexane ring are 21 kj (4.9 kcal)/mol for ferf-butyl and 2.0-2.6 kJ (0.48-0.62 kcal)/mol for bromine. Estimate the relative percentages of the alternative chair conformations you drew in the first part of this problem. 

Draw each of the following substituted cyclobutanes in its two interconverting puckered conformations (Figure 4-3). When the two conformations differ in energy, identify the more stable shape and indicate the form(s) of strain that raise the relative energy of the less stable one. (Hint Puckered cyclobutane has axial and equatorial positions similar to those in chair cyclohexane.)... 

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