Positive rotation

Rgure 2-10 Positive Rotation of Principal Material Axes from x-y Axes... 

We may return now to the polysaccharides present in the peanut for a brief consideration of the relationship of the other components present in the pectic materials to the araban constituent. All the evidence indicates that the pectic acid portion of the peanut is identical with normal pectic acid and, as was indicated in the previous section, this material, which is very stable to acid hydrolysis and possesses a high positive rotation contains a main chain which is built up of D-galac-turonic acid residues of the pyranose type. If, therefore, the araban associated with the pectic acid had been derived directly from the pectic acid by decarboxylation without intermediate hydrolysis of the poly-galacturonide, the sugar residues in the araban should also be in the pyranose form. The experimental evidence shows clearly, however, that the arabinose residues in araban are furanose in type and it follows that any hypothesis concerning the direct conversion of pectic acid into the araban by decarboxylation is untenable. 

Although a pure dL sample had not been obtained, a sample possessing a high positive rotation and lower biological activity had been isolated.2... 

The measured rate is the superposed sum of the positive rotational flow and the negative pressure flow. The rotational flows can be obtained by subtracting the negative pressure flow from the measured rate as shown in Fig. 7.32 by the open square [ ] and x-markers [x] for screw and barrel rotation, respectively. As shown in this figure, screw rotation and barrel rotation flows were the same within experimental error. The solid black line is the rotational flow predicted using Eq. f.i3. Thus and as expected, barrel rotation and the screw rotation produce the same rotational rates. 

That is, the transformation is represented as successive rotations of y, P, a about the e3, e2, and axes. A positive rotation is a counterclockwise rotation.1 Since R is unitary, it follows that the Cartesian coordinates transform as... 

In the case of 3-L-arabinose the strongly positive rotation decreases and the conductivity increment likewise decreases. As A is rather large (for the equilibrium mixture, 119.7), furanoses or hydrates must be taken into account. However, both the constants of the mutarotation and of the change of A correspond very well, namely, k + k = 0.0582,... 

The absolute configuration of all chiral amines prepared was determined by comparison with literature rotation values to be S. The (S)-enantiomers possess a positive rotation and the derived a-naphthamides elute, as in other cases, after the (//(-enantiomer on a chiral Pirkle column. 

The results are explained as indicating that the addition of triplet arylcarbenes to intramolecular double bonds is accelerated by factor of 300-800 relative to inter-molecular addition. The intramolecular addition reactions of singlet arylcarbenes exhibit much smaller rate enhancements. The most stable planar conformer of singlet (102) cannot interact with the n bond of an allyl group attached to the ortho position. Rotation about the bond connecting the divalent carbon to the ring must occur in order for an electrophilic approach to take place. This rotation will result in the loss of benzylic stabilization. In marked contrast, the first step of the triplet addition can take place with no rotation of the divalent carbon. 

The absolute configurations of helicenes have been firmly established by calculations 95 98), by X-ray analysis 99) and by synthesis l00).6 The dextrorotatory enantiomers of hexahelicene and a thiahexahelicene have been shown to possess the right-handed (P) helicity. From the correspondence of the ORD- and CD-curves of these hexahelicenes and higher helicenes positive rotations correspond in all cases with P-helicenes. 

Both spectra were almost mirror images of one another as expected from their opposite rotations. The relative intensities of the peaks were nearly proportional to the ratio of the specific rotations. The peaks at 208 and 232 nm may be assigned to the absorptions of the phenyl and ester groups, respectively. The spectral pattern is very similar to that of the copolymer 9 of TrMA with a small amount of (S)-a-methylbenzyl methacrylate illustrated in Figure 5. This also indicates that the large positive rotations of the copolymers 7-9 in Table are attributed to the helical conformation of isotactic TrMA units preferential in one screw sense. 

Complete hydrolysis of the polyglycoses gave the starting monomer. Hydrolysis with dilute acid gave an initial rise in optical rotation which was attributed to the hydrolysis of furanosidic bonds. The positive rotations suggest the presence of o-d as well as of 0-D-glycosidic linkages. The isolation... 

Maximum observed value lb) Optically active paraffine m calculated according to Brewster [Af]z of the allowed conformation having the highest positive rotation... 

Consider first a Cartesian coordinate system with unit basis vectors ei, e2, e3. We define the effect of a positive rotation about the z axis through an angle 0, corresponding to a symmetry operation G, say, as a counterclockwise rotation since... 

A clockwise rotation, as the observer looks towards the beam, defines the substance as dextrorotatory (i.e., rotates to the right) and the angle a is taken as a positive (+) rotation. If the rotation is counterclockwise the substance is described as levorotatory (i.e., rotates to the left) and the angle a is taken as a negative (—) rotation. 

---