Chair conformation The most stable

Siegel and Smith (57) suggested that, in the transition state for adsorption, the cycloalkene adopts a pseudo-chair conformation, the most stable geometry of an isolated cyclohexene (81) (Fig. 16). For example, this... 

Chair conformer The most stable conformer of cyclohexane. 

A final consideration in describing the structure of a monosaccharide is its conformation. Most aldopyra-noses adopt a chair conformation, the most stable form being that in which as many as possible of the bulkier OH and CH2OH groups are equatorial, as shown for glucose in Fig. 2.8. A corresponding envelope confor-... 

Chair conformation The most stable conformation of cyclohexane ... 

Chair conformation The most stable puckered conformation of a cyclohexane ring all bond angles are approximately 109.5°, and bonds to all adjacent carbons are staggered. 

As ring size increases, there are progressively more conformations that need to be considered. For cycloheptane, four conformations have been calculated to be particularly stable. NMR investigations indicate that the twist-chair is the most stable. Various cycloheptane derivatives adopt mainly twist-chair conformations. ... 

Neutral hexakis(methylsulfonyl)benzene (see Scheme 6.23) adopts a chair conformation. On the contrary, the tube conformer appears to be inherent in the corresponding anion-radical. The methylsulfonyl fragments at positions 1 and 4 of the bent benzene ring are nonequivalent. Moreover, one methylsulfonyl moiety is nonequivalent to all of the other five (Fabre et al. 2002). Scheme 6.23 depicts an intuitively constructed picture. Localization of spin-charge density within one methylsulfonyl group causes the attraction of the other from position 4. This makes the tube conformation the most stable in the case of hexakis(methylsulfonyl)benzene anion-radical. 

By means of ab initio calculations at the 6-3IG level, the conformation and the spectroscopic and structural properties of cyclic Ofi have been calculated (88JPC959 93JPC4023) the chair was the most stable conformation, the twist conformation (15.9 kcal moP ) and the boat conformation (17.5 kcal moP ) being higher in energy. 

Cyclohexane achieves tetrahedral bond angles and staggered conformations by assuming a puckered conformation. The most stable conformation is the chair conformation shown in Figure 3-19. Build a molecular model of cyclohexane, and compare its shape... 

Conformational energy of cyclohexane. The chair conformation is most stable, followed by the twist boat. To convert between these two conformations, the molecule must pass through the unstable half-chair conformation. 

An examination of the temperature-dependent CD spectra of (-1-) [Co-(tnls] " " and the solid state CD of (-t-) [Co(tn)3]Br3, the structure of which is known, has led to the conclusion that in solution the tris-chair is the most stable conformer by about 0.5 kJ mol over the Ids skew boat... 

Although cyclohexane is a ring structure it does have free rotation around single bonds. Cyclohexane has two main conformations. The most stable form is called the chair form, the les stable is called the boat form ... 

In the solid state and in solution, six-membered tetrahedral phosphorus compounds generally adopt a chair as the most stable ground-state conformation. However, Bentrude has shown, by nmr analysis, that the barrier to chairs twist interconversion is low in some six-membered systems (Day et al, 1984 Bentrude et al, 1984 Beres et al., 1987 Nelson et al., 1987). The twist/chair activation barrier for 1,3,2-oxazaphosphorinanes is low. Compound [79] exists in the twist conformation in the solid state and solution. Compound [80] adopts a full boat conformation, from solution nmr spectroscopy and crystal-structure analysis. 

Cyclohexane adopts a number of puckered conformations, the most stable of which is a chair conformation. In this conformation (Figure 3.7), all C—C—C bond angles are 109.5° (minimizing angle strain), and hydrogens on adjacent carbons are staggered with respect to one another (minimizing torsional strain). Thus, there is very little strain in a chair conformation of cyclohexane. 

Figure 16.8 Cyclohexane can exist in various shapes (or conformations). The most stable conformation is the chair form and a less stable one is the boat form. The two types of H atoms are labeled axial and equatorial, respectively.

Energy diagram for interconversion of chair, twist-boat, and boat conformations of cyclohexane.The chair conformation is most stable because angle, torsional, and steiic strain are at a minimum. 

The most stable conformation of trans 1 4 dimethylcyclohexane has both methyl groups in equatorial orientations The two chair conformations of trans 1 4 dimethyl cyclohexane are not equivalent to each other One has two equatorial methyl groups the other two axial methyl groups... 

If a disubstituted cyclohexane has two different substituents then the most stable conformation is the chair that has the larger substituent m an equatorial orientation This IS most apparent when one of the substituents is a bulky group such as tert butyl Thus the most stable conformation of cis 1 tert butyl 2 methylcyclohexane has an equatorial tert butyl group and an axial methyl group... 

Section 3 7 Three conformations of cyclohexane have approximately tetrahedral angles at carbon the chair the boat and the skew boat The chair is by far the most stable it is free of torsional strain but the boat and skew boat are not When a cyclohexane ring is present m a compound it almost always adopts a chair conformation... 

The following are representations of two forms of glucose The six membered ring is known to exist in a chair conformation in each form Draw clear representations of the most stable con formation of each Are they two different conformations of the same molecule or are they stereoisomers Which substituents (if any) occupy axial sites ... 

Typical carbon-oxygen bond distances m ethers are similar to those of alcohols (—142 pm) and are shorter than carbon-carbon bond distances m alkanes (—153 pm) An ether oxygen affects the conformation of a molecule m much the same way that a CH2 unit does The most stable conformation of diethyl ether is the all staggered anti conformation Tetrahydropyran is most stable m the chair conformation—a fact that has an important bearing on the structures of many carbohydrates... 

The most stable conformation of 1 3 dioxan 5 ol is the chair form that has its hydroxyl group in an axial orientation Suggest a reasonable explanation for this fact Building a molecular model IS helpful... 

All the ring substituents m p D glucopyranose are equatorial m the most stable chair conformation Only the anomenc hydroxyl group is axial m the a isomer all the other substituents are equatorial... 

The most stable conformation of cyclohexane is the chair. Electron diffraction studies in the gas phase reveal a slight flattening of the chair compared with the geometry obtained when tetrahedral molecular models are used. The torsion angles are 55.9°, compared with 60° for the ideal chair conformation, and the axial C—H bonds are not perfectly parallel but are oriented outward by about 7°. The length of the C—C bonds is 1.528 A, the length of the C—H bonds is 1.119 A, and the C—C—C angles are 111.05°. ... 

For cyclooctane, a total of 11 conformations have been suggested for consideration and their relative energies calculated. The boat-chair was calculated to be the most stable conformation. This prediction was confirmed by analysis of the temperature dependence of the F-NMR spectra of fluorocyclooctanes. The activation energy for interconversion of conformers is 5-8 kcal/mol. A few of the most stable conformations are shown below. 

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