Molar optical rotation

The molar rotation of the dendrimers 49-51 is proportional to the excess of (R,R)- or (S,S)-threitol units. This means that the chiroptical effects of threitol building blocks of opposite chirality cancel out each other. For the homo dendrimers an average positive molar optical rotation value of 146 for each (i, k)-threitol unit was calculated whereas a value of -185 resulted for each... 

A unique chiral phosphine-phosphate ligand has been applied for hydrofor-mylation reaction of alkenes. In the case of 170 this ligand can be applied for obtaining poly(propylene-aZt-Co) with the highest molar optical rotation and with the highest molecular weight ([ ]d4 = + 40°, Mw = 104400, MJMn = 1.6) [284]. 

Sharpless et al. noted an increase of the specific rotation with increasing generation number in the case of dendrimers having trimesic acid as achiral core unit and a completely chiral polyether dendrimer skeleton based on 1,2-diol branching units (Fig. 4.72) [27]. The observed molar optical rotations corresponded to... 

This indicates that the measured molar optical rotation is caused by the chiral building blocks and not by a stable conformational array of the dendrimer scaffold [83]. 

One interesting example is (+)-trans -2-ehloro-5-methyleyelohexanone (32). The sign of the Cotton effeet in its ORD spectrum is reversed on transferring it from water to -heptane (molar optical rotation at X — 330 nm and 25 °C [< ] = +382 and — 1486, respectively) [189], This can be ascribed to a diaxial/diequatorial conformational equilibrium (32a) (32b), which lies more to the left-hand side in n-heptane than in water. 

For some carbonyl compounds, a reverse in optical rotation sign has been observed when the ORD spectra were measured in solvents of different polarity. For example, (5)-5-hydroxy-l,7-diphenyl-3-heptanone is dextrorotatory in trichloromethane (molar optical rotation [interaction between the y9-ketol moiety and the solvent is responsible for the change and reversal in optical rotation with increasing solvent polarity. 

Usually, the chiroptical properties of highly cross-linked polymers cannot be measured. The asymmetry of the empty cavities can be deduced from their excellent racemate resolution ability, but under special conditions it can also be directly detected by optical activity measurements [41]. For this, the polymer is suspended in a solvent that has the same refractive index as the polymer, a technique which was developed for other types of insoluble polymers. The values of molar optical rotation thus determined are shown in Table 4.3. 

If we compare the value (—61.7°) for a polymer prepared from 1 (calculated for the molar content of 1), still containing the template, with the value —448.9° for the template monomer 1, it becomes apparent that the molar optical rotation value is considerably decreased as a result of polymerisation. This can have several causes, one being the influence of the polymer matrix. Its effect can be determined by removing the optically active template la. If the boronic acids are then converted with ethylene glycol to the corresponding achiral ester, the polymer shows a positive molar rotation [M] °546 = -1- 110.0°. Apparently, in P-E the imprints generated in the polymer make a positive contribution to the optical rotation value. Measuring the optical rotation in the solid phase allows the... 

MOLAR OPTICAL ROTATION VALUES FOR POLYMERS WITH CHIRAL CAVITIES [41]... 

The inclusion of Frechet-type dendrons around stereogenic cores such as (3/v ,4.S, 5A )-3,5-dihydroxy-4-hydroxymethyl-2,2-dimethylhexane,288 289 (1 / , 2 S) -2-amino-l-phenyl- 1,3-propanediol,290 2,5-anhydro-D-mannitol,291 and TADDOL292 produced the opposite effect. As the generation number of the attached dendrons increased, the molar optical rotation of these materials generally decreased. This trend is believed to result from perturbation of the chiral conformation by the bulky dendrons.86... 

As to the chiroptical properties of 1,6-anhydrohexopyranoses, their [M]d values can be calculated by summation of the molar, optical rotation values for the fundamental skeleton, that is, l,6-anhydro-2,3,4-trideoxy-j8-D-gZycero-hexopyranose (26), and, either the values of the partial, molar contributions of the hydroxyl groups372,373 (see Scheme 3)... 

Since the magnitude of the Effect is proportional to the concentrations of both the environment substance and the complex, a series of equations have been developed for observed Pfeiffer rotation, specific Pfeiffer rotation, and molar Pfeiffer rotation which are analagous to those for observed optical rotation, specific optical rotation, and molar optical rotation (3.it,6,10). These are... 

Despite the presence ofcw-substituted units, the molar optical rotations are considerably higher than those of the low molecular analog (12 .32 )-/rauy-l,3-dimethylcyclopentane. suggesting that chiral conformations are adopted by the dissolved polymer58. 

Poly(methylene-1,3 -cyclopentane) synthesized in the presence of (-)-(R,R)-3 and methylalumoxane revealed a molar optical rotation of [0] 4O5 = +51.0° (c 8.0, CHCI3), whereas the polymer analogously prepared using the enantiomer (+)-(S,S)-3 showed a value of [0]284O5 = -51.2° (c 8.0, CHCI3). These findings are consistent with the formation of polymers with main-chain chirality. [9a]... 

Table 2-4 Molar optical rotation values for polymers with chiral cavities [133].

Figure 2. Extinction (-------), molar optical rotation ( ), and dichroic absorp-...

Table 4-8. Molar Optical Rotation [ ]fs of Various Low-Molar-Mass Compounds R— CH(CH3)—(CH2)>-—CHb in the Liquid State at 589 nm and 25° C...

The molar optical rotation of optically active it-poly(a-olefins) depends not only on the wavelength and temperature, but also on the optical purity of the monomers (and thus, also, of the polymers) (Figure 4-23). The molar optical rotation of these polymers remains constant when the optical purity of the monomer is high. 

The molar optical rotation of a polymer obtained by polymerizing a monomer of given optical purity under various conditions depends on the tacticity of the resulting polymer (Figure 4-24). Extrapolation of the reciprocal optical rotation to that of the tactic polymer allows the molar optical rotation of the latter to be obtained. 

The dependence of the molar optical rotation of poly(a-olefins) on the wavelength of the polarized light used can be well represented by the one-term Drude equation. The constant Xo is of approximately the same magnitude for polymers and their hydrogenated monomers (Table 4-11). For polymers. 

Figure 4-23. Molar optical rotation [< >] of various methanol insoluble poly (a-olefins) in hydrocarbon solutions as a function of the optical purity,/, of the initial monomer (P. Pino, F. Ciardelli, G. Montagnoli, and O. Pierono).

The molar optical rotation of poly(a-olefins) decreases with increasing temperature. This is interpreted as the melting of relatively long, left-... 

The molar optical rotation of configurational copolymers of (S) and (R) isomers of the same monomer is generally, in the case of poly(a-olefins), a hyperbolic and not a linear function of the optical purity of the monomers. Thus, the molar optical rotation of the copolymers is always greater than that obtained by additivity rules. Whether this is caused by tactic blocks in the polymers or by mixtures of (S) and (R) unipolymers has not been established yet. 

With the Kramers-Kronig transforms (eqn [9]), the frequency dependence of the molar optical rotation (ORD) can be obtained as follows ... 

The molar optical rotation of a polymer obtained by polymerizing a monomer of given optical purity under various conditions depends on the... 

---