Positive only

The reduction of 1 l-keto-9 -H steroids gives an lla-ol, due to the fact that ring B or C must be in the boat form. The presence of bromine at the 2a-, 5a- and 12a-positions does not afifect greatly the isomer composition resulting from reduction of 3-, 6- and 11-ketones respectively. When in a 7-keto steroid the bromine is in the 6a-position a mixture of la- and 7 -ols results when the bromine is in the 6 -position only the 7jS-hydroxy compound is obtained. " The presence of bromine in the 16a- or 16 -positions seems to reduce the amount of 17 -alcohol formed. ... 

Electron pair on ring oxygen can stabilize carbocation at anomeric position only. 

Draw a Lewis structure (or a series of Lewis structures) for nitrobenzenium ion. Where is the positive charge Examine the electrostatic potential map for nitrobenzenium ion. Where would you expect electron-donor substituents to have the greatest stabilizing effect (consider meta and para positions only) Which is the more stable, meta or para-nitrotoluenium ion (intermediates in nitration of toluene) Compare electrostatic potential maps to that for nitrobenzenium ion. Does your result suggest that methyl acts as an electron donor ... 

In the cases 6-R-3-Y and 5-R-2-Y, the relation of R to Y corresponds to the para relation in benzene. When Y is in the 4-position, only meta-type (2-R or 6-R) substituents are possible. With R in the 2-position, aside from the one para-type relation (5-R-2-Y), two different metatype relations (4-R- and 6-R-2-Y) are possible, and the reactivity need not be the same for these two. Two ways suggest themselves to overcome this difficulty One might attempt to define separate a-values for substituents, depending not only on the relative position with respect to the side-chain, as in and Op, but also in relation to the heteroatom ... 

An acid-catalyzed substitution of a 6-oxo group on 2-aminopteridine-4,6-dione with hydrogen chloride in alcohols (65-100°, 3 hr, 80% yield) represents a convenient synthesis of the 6-alkoxy analogs. The reaction proceeds also with pteridine-2,4,6-trione and its 1-methyl and 1,3-dimethyl derivatives. While methoxylation of 2,4,7-trichloro-quinoline gives about equal amounts of 2- and 4-substitution, acid-catalyzed hydrolysis gives specific reaction at the 2-position only. ... 

The information on intranuclear and irdemuclear activations in bieyelie azines and nitronaphthalenes is summarized here. In the transition states for azanaphthalenes and their nitronaphthyl analogs illustrated in Sehemes II-IV, the leaving group position is kept eonstant in each comparison and it is assigned either the 2- or the 4-position only, for reasons diseussed under the aetivation-numbering system later in this subseetion. 

For exponential kernel (1.77) t2 = 2t2 = t2. Consequently d2g(o))/da>2 o becomes positive only at k > 1/2. For this condition, which is also seen from Eq. (1.94), Kj(t) changes sign at sufficiently large t and the spectrum g(co) is split into two lines with a minimum in between. In contrast, the second moment of the kernel (1.95) diverges and... 

Alkanes, arylalkanes, and cycloalkanes can be aminated, at tertiary positions only,... 

The structure of amylopectin according to Meyer is shown in Fig. 65. The single reducing end group is indicated by A all other terminal units are attached at the 1-position only. 

Fig. 45. Molecular structure of the anhydrous imidazole associate of / 1111 (H atoms of the carboxyl groups indicate putative atomic positions only O atoms dotted N atoms hatched)...

Note that thanks to our assumption of charge-state equilibration, this depends on position only via the em(r) occuring in (3) and (4). 

Distorted trigonal bipyramidal configuration, 170 with N and Br atoms in frows-positions. Only one diastereoisomer of 36 appears in die solid state. 

Hamilton s principle is equivalent to the statement that for the actual motion the average kinetic energy approaches the average potential energy as closely as possible. If the potential energy is a function of position only the equivalent mathematical statement is... 

Since the nuclei are massive compared to electrons, m/M << 1, they move so slowly in a molecule that the electrons can always maintain their optimal motion at each Q. The electronic wave functions may therefore be assumed to depend on the nuclear positions only and not on their momenta, i.e. Naip Q,q) — 0. The electrons are said to follow the nuclei adiabatically. Under these assumptions equation (30) reduces to... 

Even though this contribution is always negative, the total capacity must be positive - otherwise the capacitor would accumulate charge spontaneously. Thus Eq. (17.4) is only valid if f > rjm, so that there is no electronic overlap between the two plates. Similarly the use of a macroscopic dielectric constant in Eq. (17.5) presupposes a plate separation of macroscopic dimensions, and again the total capacity is positive. Only unphysical models or bad mathematical approximations can produce negative interfacial capacities, which enjoyed a brief spell of fame under the name of the Cooper-Harrison catastrophe [2]. 

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