Axial bond

Draw the axial bonds before the equatorial ones alternating their direction on adjacent atoms Always start by placing an axial bond up on the uppermost carbon or down on the lowest carbon... 

Conformational inversion (ring flipping) is rapid in cyclohexane and causes all axial bonds to become equatorial and vice versa As a result a monosubstituted derivative of cyclohexane adopts the chair conforma tion in which the substituent is equatorial (see next section) No bonds are made or broken in this process... 

Axial bond (Section 3 8) A bond to a carbon in the chair conformation of cyclohexane oriented like the six up and down bonds in the following... 

The 12 hydrogen atoms of cyclohexane do not occupy equivalent positions. In the chair conformation six hydrogen atoms are perpendicular to the average plane of the molecule and six are directed outward from the ring, slightly above or below the molecular plane (see Fig. 1.6). Bonds which are perpendicular to the molecular plane are known as axial bonds, and those which extend outward... 

Fig. 1. (a) The glucopyranosyl basic unit, where e = equatorial and a = axial bond (b) amylose with equatorial—axial intemnit bonding (the C—H axial... 

In the absence of steric factors e.g. 5 ), the attack is antiparallel (A) (to the adjacent axial bond) and gives the axially substituted chair form (12). In the presence of steric hindrance to attack in the preferred fashion, approach is parallel (P), from the opposite side, and the true kinetic product is the axially substituted boat form (13). This normally undergoes an immediate conformational flip to the equatorial chair form (14) which is isolated as the kinetic product. The effect of such factors is exemplified in the behavior of 3-ketones. Thus, kinetically controlled bromination of 5a-cholestan-3-one (enol acetate) yields the 2a-epimer, (15), which is also the stable form. The presence of a 5a-substituent counteracts the steric effect of the 10-methyl group and results in the formation of the unstable 2l5-(axial)halo ketone... 

Axial bonds The six axial bonds, one on each carbon, are parallel and alternate up-down. 

Axial bond (Section 4.6) A bond to chair cyclohexane that lies along the ring axis perpendicular to the rough plane of the ring. 

Atorvastatin, structure of, 105. 516 ATP (see Adenosine triphosphate) ATZ, see Anilinothiazolinone, 1031-1032 Aufbau principle. 6 Axial bonds (cyclohexane), 119 drawing, 120 Azide, amines from, 929 reduction of, 929 Azide synthesis, 929 Azo compound, 944 synthesis of, 944-945 uses of. 945... 

The first of these is that when the symmetry of the two groups at the ends of the axial bond demands a barrier with six equivalent... 

The length of the axial bond would be expected on all theories to be important. The barrier height does decline from ethane to methyl silane to methyl germane, but of course the bonded atoms are different. Unfortunately reliable values are not available for dimethyl mercury, dimethyl acetylene, and similar molecules with still longer bonds. An apparent exception is provided by methyl mercaptan and methyl alcohol. The latter, with the shorter axial bond, has the lower barrier. 

Rearrangement of sulfoxides 38a, b exhibited the interplay of several conformational factors. Both diastereomers afford predominant axial (trans) alcohol, but with opposite absolute configuration. The (R, R)-diastereomer strongly prefers the exo-transition state, whereas the (R, S)-isomer prefers the endo conformation. Hoffmann interprets these results in terms of an approximately 3-fold preference for the exo-transition state but a 6-fold preference for formation of an axial bond, these effects reinforcing each other in one isomer but opposing each other in the second. 

Avogadro s constant The number of objects per mole of objects (Na = 6.022 14 X 102 mol ). Avogadro s number is the number of objects in one mole of objects (that is, the dimensionless number 6.022 14 XlO2 ). Avogadro s principle The volume of a sample of gas at a given temperature and pressure is proportional to the amount of gas molecules in the sample V n. axial bond A bond that is perpendicular to the molecular plane in a bipyramidal molecule, axial lone pair A lone pair lying on the axis of a bipyramidal molecule. 

I have developed a simple theory of these potential barriers, described in the following paragraphs. According to this theory, the potential barriers are not a property of the axial bond itself, but result from the exchange interactions of electrons involved in the other bonds (adjacent bonds) formed by each of the two atoms, as determined by the overlap between the parts of the adjacent bond orbitals that extend from each of the two atoms toward the other. 

The hybrid orbital has cylindrical symmetry, and accordingly the introduction of d character and f character in the axial bond itself does not lead to an interaction dependent on the relative azimuthal orientation of the two groups. 

Also, the height of the barrier changes from molecule to molecule in the predicted way. The barrier interaction involves the same integral over the radial parts of the wave functions as the axial bond itself, and it would accordingly be expected that... 

The general qualitative agreement with experiment provides support for the theory that the potential barriers to internal rotation result from the interaction of adjacent hybrid bond orbitals with a small amount of / character. The magnitude of the potential barriers, about 4 per cent of the energy of the axial bond in case that there are three interacting bonds on each of the two atoms and proportionately less for a smaller number of bonds, is also reasonable. A detailed quantum-mechanical treatment of restricted rotation carried out along the lines sketched here should yield results that would permit a detailed test of the theory to be made in the meantime I believe that the above simple treatment and the extensive empirical support of the theory provide justification for it. 

On each carbon, one bond is directed up or down and the other more or less in the plane of the ring. The up or down bonds are called axial (a) and the others equatorial (e). The axial bonds point alternately up and down. If a molecule were frozen into a chair form, there would be isomerism in monosubstituted cyclohexanes. For example, there would be an equatorial methylcyclohexane and an axial... 

Many types of phosphorus-phosphorus bonds are known, but it is rare to find such bonds in hexacoordinated phosphorus compounds (with the exception of 57). Cavell reported in 1998 the reaction of PCI5 with phenylbis(o-(trimethyl-siloxy)phenyl)phosphane, yielding the corresponding bischelate 61 in decent yield (52%) [99]. The octahedral nature of the central phosphorus atom was unambiguously determined by X-ray structural analysis. Two short axial bonds (2.202 A) lie perpendicular to the pseudo-octahedral equatorial plane. 

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