Enantiomorphous group

Note that these are specified by Ul and Lk, respectively, i.e., begin with a capital letter (see Section 1.1.2.1.). Analogous models with three-dimensionally enantiomorphic groups F,F are known as geometric enantiomers (see Section 1.1.3.3.). Given the modern use of fundamental terms (see Section 1.1.2.1.), this designation appears inappropriate today. 

Four stereoisomers can be produced in the reaction. All reaction products have chirality centres at C2 and C6, the absolute configuration of which can be specified by R and S. Compounds A and B additionally possess a pseudo chirality centre at Cl since there are two constitutionally identical but enantiomorphic groups attached to this position. By applying the CIP rules, Cl in A has the stereodescriptor r, whilst Cl in B has the stereodescriptor s. The groups attached to Cl in C and D are homomorphic, therefore Cl in these compounds is a pro chirality centre. 

Tropatepine exhibits a very interesting structural feature. Normally, compounds with differently configured double bonds are diastereomers of each other. However, in this instance, since two enantiomorphic groups are attached to one end of the double bond, they are in fact enantiomers. It is quite easy to see that both formulae can be transformed into one another by mirror reflection. Tropatepine is therefore chiral. It is used clinically as the racemate. 

Morphine alkaloids are a subgroup of isoquinoline alkaloids and are derived biogenetically from laudanosine bases by oxidative phenolic coupling/6,7 Alkaloids of the opposite enantiomorphic group occur in several Japanese Sinomenium and Stephania species, the most important compounds being sinomenine, hasubanonine, metaphenin, and protometaphenine. 

Optical activity is observable in any direction for crystals belonging to the two cubic enantiomorphic classes 23 and 432, but, in general, optical activity can only be observed in certain symmetry limited directions. For example, optical activity in the other enantiomorphic classes is only readily observed in a direction fairly close to an optic axis. This is because the different refractive indices that apply to light polarised vertically and horizontally masks the effect in directions further from an optic axis. In the non-enantiomorphic groups, no optical activity is found along an inversion axis or perpendicular to a mirror plane. Thus no optical activity occurs along the optic axis... 

Classically, there is only one way to obtain a noncentrosymmetric crystal packing. The use of enantio-merically pure dipolar compounds ensures crystallization in one of the 11 enantiomorphic groups, whereof 10 show a piezoelectric effect. Only five (namely, those featuring an unique rotational axis 1, 2, 3, 4. 6) of the enan-tioinorphic groups that are piezoelectric also allow for pyroelectricity (see Table 1). At present, there is no design eoneept with whieh to obtain a polar point group by spontaneous nueleation. 

The base boiled in methyl alcoholic solution with methyl iodide and potassium hydroxide, forms a gelatinous methiodide, which was converted by silver chloride into the methochloride. The latter when boiled with 20 per cent, solution of sodium hydroxide, produced a mixture of methine bases, which were separated as the methiodides into 0-methylbebeerine-methine methiodide B, m.p. 237° (cf. p. 375), and a lasvorotatory form, m.p. 190°, which proved to be the lasvo-enantiomorph of d-O-methyl-bebeerinemethine methiodide (form C, p. 375). Chondrofoline therefore belongs to the bebeerine type represented by formula (III). In it R = H, the single phenolic hydroxyl is at ORj or OR4 and the remaining groups, OR2, OR 3, OR or alternatively ORj, OR2, OR 3 are methoxyl groups (King,i 1940). 

In literature, SOHNCKE space-group types are often termed chiral space groups , which is not correct. Most chiral molecular compounds do not crystallize in a chiral (enantiomorphic) space group. For details see [86]. 

Finally, one should be cautioned that, occasionally, substances form chiral single crystals of nearly racemic composition. For example, hexahelicene crystals grown from racemic solutions apparently undergo spontaneous resolution, displaying the enantiomorphic space group P2[2,2, however, the e.e. in the crystal is only —2%. This material (and probably others as well) has a lamellar, twinned structure in which alternating layers, 20 p,m thick, of optically pure (/ )-( + )-and (M)-( — )-hexahelicene are perfectly aligned to build up the observed crystal (266). 

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