Molecule dimer

Here, superscript F denotes relatively "free" molecules (weak physical forces), and D denotes relatively "bound" or "dimerized" molecules ("chemical" forces). 

All the other aluminium halides are covalently bonded with aluminium showing a coordination number of four towards these larger halogen atoms. The four halogen atoms arrange themselves approximately tetrahedrally around the aluminium and dimeric molecules are produced with the configuration given below ... 

Irradiation of an aqueous solution of thymine (111 R = Me) in the presence of air produces (irreversibly) at least four products (111 R = CH20H, CHO, CO2H or H), possibly via dithymine peroxide , a linear dimeric molecule (112), The significance of these reactions has been discussed (65MI21300). 

Many proteins that switch off or on gene expression in bacteria are dimeric molecules, and the DNA sequences that they specifically recognize are palindromic at their ends. The twofold symmetry of the protein is therefore matched by twofold symmetry at the ends of the recognition sequence. 

Each of the membranes acts like a hard wall for dimer molecules. Consequently, in parts I and III we observe accumulation of dimer particles at the membrane. The presence of this layer can prohibit translation of particles through the membrane. Moreover, in parts II and IV of the box, at the membranes, we observe a depletion of the local density. This phenomenon can artificially enhance diffusion in the system. In order to avoid the problem, a double translation step has been applied. In one step the maximum displacement allows a particle to jump through the surface layer in the second step the maximum translation is small, to keep the total acceptance ratio as desired. 

This peculiar form applies when a dimeric molecule dissociates to a reactive monomer that then undergoes a first-order or pseudo-first-order reaction. This scheme is considered in Section 4.3. Unless one can work at either of the limits, the form is such that a numerical solution or the method of initial rates will be needed, since the integrated equation has no solution for [A]r. 

The last case we shall treat is a more difficult one mathematically. Consider a dimeric molecule A that is converted to products upon reaction with B by way of a monomeric A intermediate. The net reaction is A2 + B = P + P2, and the scheme is... 

The solid state structure of 33 reveals a dimeric molecule with an eight-membered B2C2N2O2 heterocyclic ring in a chair conformation. The N—B and B—O bond lengths of 1.585(2) and 1.541(2) A, respectively, as well as the C—N and C—O bond lengths of 1.294(3) and 1.285(3) A, respectively, indicate delocalization of the Ti-electron density in the acylamino moiety [65]. 

A series of (phoshinoyloxy)- [71], (phosphorylamino)- [72], (sulfonyloxy)-[73-78] and (seleninoyloxy)boranes [79] are also known, however, only monomeric or dimeric molecules with similar structures and conformations to I-III (Fig. 12) have been reported so far. 

Due to the steric requirement of these substituents the formation of a columnar structure with infinite M M interactions is inhibited, and only the association of pairs of molecular units is allowed. The Ni Ni distance is 3.21 A [164]. If the same compound is crystallized in the presence of benzimidazole, the [Ni(dmg-BF2)2]2 dimer units are sandwiched between sheets of benzimidazole molecules due to n-n interactions resulting in an increased Ni Ni separation of 3.358 A [165]. With anthracene the n-n interactions seem to be stronger, because in this case the parent dimer molecule is cleaved. Each monomer now has a conformation of type B (Fig. 32) and is sandwiched by anthracene molecules [166]. Compound 121 has the same configuration [163d]. 

Fig. 7. Snapshots from a smectic-A phase of liquid crystal dimer molecules composed of two Gay-Berne mesogens linked by a flexible alkyl chain. Data from [112] supplied by Dr M R Wilson, University of Durham...

The modification of molecular conformation from the highly strained non-isolable dimer molecule to the V-shaped dimer molecule (6 OPr-dimer) is explained in terms of relaxation of the strain energy due to the bond angle in the non-isolable dimer, which accumulated during the cyclobutane formation. Therefore, strictly speaking, the process going from the non-isolable dimer into the V-shaped dimer (6 OPr-dimer) is not a... 

Moreover, since the repeating unit in a-type linear polymers is about 7.5 A, according to a molecular model evaluation, the stacks in the starting crystals prefer to have repeating units of a similar length (L). However, L (5.932 A) in 2 OPr-a-dimer crystals is apparently shorter than the favourable distance (—7.5 A). On the other hand, in the 2 OPr-a-dimer-PrOH complex, reactant dimer molecules are separated from each other by a more suitable distance (L = 6.736 A). 

By arguments very similar to those used to derive Eqs. (87)-(89), one can show that the equilibrium constants for exchange reactions of ionic vapor dimer molecules... 

In case a polymer sample weighs W grams and contains n, monomer molecules each Molecular weight Mls n2 dimer molecules of Molecular weight M2, n3 trimer molecules of Molecular weight M3.ni i-mer... 

The structure of [Rh(CO)2Cl]2 in the solid state83) shows association between the dimer molecules, so that for any one dimeric unit there will be a share in five metal-metal bonds [one / (Rh-Rh) = 312 pm four r(Rh-Rh) = 331 pm]. The chlorine atoms bridge the short (intradimer) metal-metal bond. The b.e.cs to the heat of disruption can be written,... 

In principle, dimeric molecules may also be made out of different halves leading to asymmetric compounds. Different substituted arylamines have been coupled by Thompson et al. [66]. Tme bipolar compounds with a different electronic character in each half will be discussed in Section VI in the context of their redox properties. Despite their polar character, the tendency toward crystallization can be low, and amorphous films are obtained. 

Light is generated upon relaxation from the excited state to a ground state that is repulsive, e.g., Xe+Cl. This condition is extremely favorable for population inversion, i.e., the number of excited dimer molecules is greater than the number of dimer molecules in the ground state, a condition necessary for light amplification... 

Hogan (H12) obtained Rc values of 0.01-10 C/kg. With dibutyl phthalate, however, he reports a mode of atomization in which no liquid jets could be seen with a microscope and for which Rc values of 105 C/kg were measured, corresponding to singly ionized dimer molecules. No particles could be formed with silicone pump oil, whereas charges of 200-400 C/kg were obtained with suspensions of either Cab-0-Sil4a or carbon in glycerine. 

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