Cyclohexane geometry

In both cts-and rrans-4-tertiary butyl-l-chlorocyclohexane30Sb the bulky tertiary butyl group will be equatorial. In these two molecules only a small deviation from the ideal cyclohexane geometry was found for their rings. 

The same group has investigated medium effects on the conformational equilibria of halogenocyclohexanes. A model of fixed cyclohexane geometry and constant C-hal bond dipole moment has been employed to calculate the dipole moments and solvent dependence of conformational equilibria of a series of mono- and di-halogenocyclohexanes. It is then possible to calculate the vapour state —AG values. 

Pentaphenylantimony [2170-05-0], C3QH23Sb, has attracted considerable attention because it possesses square-pyramidal rather than the expected trigonal-bipyramidal geometry, both ia the sohd state and ia solution. The cyclohexane solvate (C3H ) Sb 1/2 and penta-4-tolylantimony... 

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°. ... 

Sclutlcn The geometry optimization reveals that the structure of formaldehyde in cyclohexane is essentially the same as it is in acetonitrile. Here are the predicted frequency shifts with respect to the gas phase for the two media ... 

Examine the geometry of norcarane. What is the conformation of the cyclohexane ring Choose a name (chair, twist boat, half-chair, etc. see Chapter 5, Problem 4) that accurately describes its shape. The bridgehead hydrogens in norcarane are cis. Do you think a trans stereoisomer is possible Explain. 

In addition to the chair conformation of cyclohexane, a second arrangement called the twist-boat conformation is also nearly free of angle strain. It does, however, have both sleric strain and torsional strain and is about 23 kj/mol (5.5 kcal/mol) higher in energy than the chair conformation. As a result, molecules adopt the twisl-boat geometry only under special circumstances. 

Anti periplanar geometry for E2 reactions is particularly important in cyclohexane rings, where chair geometry forces a rigid relationship between the substituents on neighboring carbon atoms (Section 4.8). As pointed out by Derek Barton in a landmark 1950 paper, much of the chemical reactivity of substituted cyclohexanes is controlled by their conformation. Let s look at the E2 dehydro-halogenation of chlorocyclohexanes to see an example. 

Substituent groups on the steroid ring system can be either axial or equatorial. As with simple cyclohexanes (Section 4.7), equatorial substitution is generally more favorable than axial substitution for steric reasons. The hydroxyl group at C3 of cholesterol, for example, has the more stable equatorial orientation. Unlike what happens with simple cyclohexanes, however, steroids are rigid molecules whose geometry prevents cyclohexane ring-flips. 

Eulerian two-fluid model coupled with dispersed itequations was applied to predict gas-liquid two-phase flow in cyclohexane oxidation airlift loop reactor. Simulation results have presented typical hydrodynamic characteristics, distribution of liquid velocity and gas hold-up in the riser and downcomer were presented. The draft-tube geometry not only affects the magnitude of liquid superficial velocity and gas hold-up, but also the detailed liquid velocity and gas hold-up distribution in the reactor, the final construction of the reactor lies on the industrial technical requirement. The investigation indicates that CFD of airlift reactors can be used to model, design and scale up airlift loop reactors efficiently. 

The energy and geometry data listed in Table 2.5 show that the effect of solvent bulk (computed for cyclohexane, toluene, diethylether chloroform, THF, and methanol by PCM model), decreases the activation energy, increasing asynchronicity for the [4 + 2] cycloaddition reactions. 

Zinc complexes of cyclohexane-1,2-dione bis(thiosemicarbazone) have been formed in the neutral and doubly deprotonated form. The X-ray structures show distorted square-based pyramidal geometries for both complexes [ZnL(OH2)] and [Zn(H2L)Cl]Cl with the water or chloride occupying the axial position.886 The binuclear complex bis[l-phenylglyoxal bis(3-piperidylthiose-micarbazone)zinc] was synthesized by electrochemical methods and reveals a Zn2L2 with two tetradentate bis-thiosemicarbazone ligands bridging the metal centers.887... 

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