Twin dimer

Fig. 21 Chirality control by circularly polarized light. The molecules used are bent-shaped twin dimer shown in the top, which has azo-linkages at both arms and shows ShiCa to B4-like phase. By CPL irradiation, almost 100% ee is obtained. In the photo taken between decrossed polarizers, only a very tiny darker domain can be seen in the lower region in a 3-mm domain [21]...

Fig. 22 (a) IR absorption spectra of a bent-shaped twin dimer, (b) Vibrational CD spectra in two chiral domains stabilized by right- and left-CPL [64]... 

Fig. 15 Chemical structures of the monomer and twin dimer, and schematic representation of molecular arrangement in the mixture of the monomer and twin dimer in the...

These Twin dimers have recently received attention as monodisperse models for polymeric mesogens of similar constitution. ... 

Scheme 8. Generation of nonsymmetrical liquid crystalline dimers, twin dimers and side chain liquid crystalline polymers by specific hydrogen bonding interactions.

After reaction of the first twin side of 33 by spiro dimerization, for instance as dienophile, the second half can theoretically react either as dienophile or as diene (Fig. 6.27). Thus, a pyrano/spiro pair (reaction of the left twin as diene and the right twin as dienophile), a pyrano/pyrano pair, or a spiro/spiro couple (reaction of... 

FIGURE 6.27 Regioselectivity of spiro-pyrano link formation upon dimerization of the o-QMs derived from twin-tocopherol 33. 

Twin molecules consisting of oxadiazoles have been made by coupling smaller oxadiazoles such as OXD-7 (17) which was introduced by Saito and Tsutsui [59] to dimers (18). The glass-forming capability was improved with an increase in Tg from 77°C (OXD-7) to 186°C (dimer) [60, 61]. 

Note 2 A liquid-erystal dimer or mesogenic dimer is sometimes known as a twin mesogen. Use of the terms dimesogenic compounds and Siamese-twin mesogen for liquid-crystal dimer or mesogenic dimer is not recommended. 

A classical type of dimerization of heterocyclic compounds is the formation of a twin molecule consisting of the same fragments. Such a reaction is known for 2-benzopyrylium salts. Thus, the reduction of the 2-benzopyry-lium salt 261 by zinc dust leads to the intermediate radical 262, which is dimerized in situ to the bisisochromene 263 (76KGS999) (cf. Section IV, B). 

How is the dimeric molecular nature of elemental H reflected in its physical properties The boiling point is low (20 K) such that hydrogen is a gas at room temperature and the associated heat of vaporization (0.8 kJ mole-1) is very low in comparison to the H-H bond dissociation energy. That is, there are strong interactions between pairs of H atoms but very weak interactions between the dimers themselves. H2 is just He (bp = 4K, AHVi = 0.08 kJ mole-1 with atoms containing twin nuclei It has molecular orbitals that are modified atomic orbitals and can be understood in the same fashion. 

Figure 23 Synthesis of twin discotic dimer and branched oligomers from CTTV-7 mesogens connected with a hexadecane spacer. (From Ref. 76.)...

Fig. 6. Cyclization and polymerization of proteins. Two approaches that employ inteins for the generation of circular recombinant protein, split intein system (A), and TWIN system (B), are demonstrated. (A), The target protein is inserted between the C-terminal intein (C-intein) and the N-terminal intein (N-intein) segment. After spontaneous intein assembly, the standard splicing reaction results in excised intein and cyclized target protein. (B), The two intein systems sandwich the target protein between two intein-CBD tags. Controlled C- and N-terminal intein cleavages lead to target protein owning both N-terminal cysteine and C-terminal thioester. Whereas the intramolecular condensation forms cycUzed proteins, intermolecular reaction gives dimeric and polymeric proteins.

Figure 6.4. (a) Schematic view of a penetrating twin (b) cross section of the nucleus of a penetrating twin viewed along the [110] direction. The dashed lines are dimer bonds. Surface-bonded hydrogen atoms are not depicted [99],... 

Rectystallization of 7 from dichloromethane affords single crystals which are suitable for X-ray diffraction analysis. Unfortunately, Because of a twinning problem, the results of the crystal measurements were not satisfactory for the determination of precise geometric parameters. However, the molecular array of 7 has been elucidated and the results are shown in Fig. 1. The analysis revealed that 7 is a new type of silicate dimeric species. 

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