Donor-acceptor interaction. See

Aromatic, donor-acceptor interactions (see section 1.3.2) Clipping is the most... 

A complex in general is any species formed by specific association of molecules or ions by donor-acceptor interactions (see Topic C9). In aqueous solution the most important complexes are those formed between a metal cation and ligands, which may be ions (e.g. halides, cyanide, oxalate) or neutral molecules (e.g. ammonia, pyridine). The ligand acts as a donor and replaces one or more water molecules from the primary solvation sphere, and thus a complex is distinct from an ion pair, which forms through purely electrostatic interactions in solvents of low polarity (see Topic El). Although complex formation is especially characteristic of transition metal ions it is by no means confined to them. 

For example (a) Bengs H, Renkel R, Ringsdorf H, Baehr C, Ebert M, Wendorff JH (1991) Makromol Chem Rapid Commun 12 439 (b) Praefcke K, Singer D, Kohne B, Ebert M, Liebmann A, Wendorff JH (1991) Liq Cryst 10 147. For electron-donor acceptor interactions, see for example (a) Kosaka Y, Kato T, Uryu T (1994) Macromolecules 27 2658 (b) Schleeh T, Imrie CT, Rice DM, Karasz FE, Attard GS (1993) J Polym Sci Part A Polym Chem 31 1859... 

An expedient and stereoselective synthesis of bicyclic ketone 30 exemplifies the utility and elegance of Corey s new catalytic system (see Scheme 8). Reaction of the (R)-tryptophan-derived oxazaboro-lidine 42 (5 mol %), 5-(benzyloxymethyl)-l,3-cyclopentadiene 26, and 2-bromoacrolein (43) at -78 °C in methylene chloride gives, after eight hours, diastereomeric adducts 44 in a yield of 83 % (95 5 exo.endo diastereoselectivity 96 4 enantioselectivity for the exo isomer). After reaction, the /V-tosyltryptophan can be recovered for reuse. The basic premise is that oxazaborolidine 42 induces the Diels-Alder reaction between intermediates 26 and 43 to proceed through a transition state geometry that maximizes attractive donor-acceptor interactions. Coordination of the dienophile at the face of boron that is cis to the 3-indolylmethyl substituent is thus favored.19d f Treatment of the 95 5 mixture of exo/endo diastereo-mers with 5 mol % aqueous AgNC>3 selectively converts the minor, but more reactive, endo aldehyde diastereomer into water-soluble... 

In this section, we present a unified picture of the different electronic effects that combine to determine methyl rotor potentials in the S0, Sp and D0 electronic states of different substituted toluenes. Our approach is based on analysis of ab initio wavefunctions using the natural bond orbitals (NBOs)33 of Weinhold and cowork-ers. We will attempt to decompose the methyl torsional potential into two dominant contributions. The first is repulsive steric interactions, which are important only when an ortho substituent is present. The second is attractive donor-acceptor interactions between CH bond pairs and empty antibonding orbitals vicinal to the CH bonds. In the NBO basis, these attractive interactions dominate the barrier in ethane (1025 cm-1) and in 2-methylpropene (1010 cm-1) see Figure 3. By analogy, donor-acceptor attractions are important in toluenes whenever there is a substantial difference in bond order between the two ring CC bonds adjacent to the C-CH3 bond. Viewed the other way around, we can use the measured methyl rotor potential as a sensitive probe of local ring geometry. 

Stoddart and coworkers [112-115] cyclized bis(bipyridyl)s in the presence of crown ethers to obtain a [2]catenane at a yield of 70%. It is illustrated in Fig. 37. The high yield can be attributed to the 7i-donor-acceptor interaction between the ring and the axle. It was shown that one of the two intercrossed rings moves around the other. The group of Stoddart [116-118] reported [3-5] catenanes (see Fig. 38 for [3]catenane). The [5]catenane of Stoddart et al. [118] was named olympiadane , because it resembles the symbol logo of International Olympic Games, as seen in Fig. 39. 

Figure 2.21 Leading sigma- (left) and pi-type (right) donor-acceptor interactions of representative TM monofluorides (see Table 2.5).

Figure 3.109 Leading donor-acceptor interactions of cbb bbb(A)+ (left) and obb- bbb (right) type in B6H10 see Eqs. (3.256a) and (3.256b) in the text.

As expected, the strongest delocalizations are the four cr—>-t donor-acceptor interactions around each ctBb bond, including two strong interactions with t,W antibonds of the second type (see Fig. 3.113, left)... 

Figure 5.6 Correlated variations of energetic (AE0...h), geometrical (Ro-e and Ai AH), and vibrational (Avah) properties of H-bonded water complexes (H20- -HA, A = F [crosses], OF [circles], NH2 [triangles], and CH3 [squares] with respect to donor-acceptor interaction AEn(Jd2) (abscissa, 1 kcalmol 1 tick marks). Vertical tick marks in each panel correspond to the quantity being plotted (a) AAo-h, 1 kcalmol 1 (b) Ro-e, 0.1 A (c) A Ah, 0.001 A and (d) Avah, 100 cm 1. (See Table 5.7 for numerical values.)...

The principal intermolecular donor-acceptor interactions of this weakly bound complex are found to be of 7tcc-OBrBr form (3 x 0.20 kcalmol-1), as illustrated in Fig. 5.41(b). A prominent feature of Br2 (and other heavy halogens) is the nearly pure-p character of the bromine bonding hybrid, resulting in a conspicuous backside lobe on the OBrBr antibond (see Fig. 5.41(b)) that is effective in end-on complexation to the pi-donor face of benzene. The unusually small energy separation between donor and acceptor NBOs,... 

See also Axial dispersion aerosols, 1 774-775 aqueous, 18 292 behavior of, 15 685-690 chemical processing aids, 8 705-711 chromatic, 11 134 classification, 8 698-699 colorants for plastics, 7 360-361 donor-acceptor interactions, 8 707-708 electrostatic repulsion, 8 732-734 in filled networks, 22 572 of filled polymers, 11 307-308 flow, 8 726-730 flushing, 8 711... 

New brush-type phases (donor-acceptor interactions) are appearing all the time. " Examples are stationary phases comprising quinine derivatives and trichloro-dicyanophenyl-L-a-amino acids as chiral selectors. Quinine carbamates, which are suitable for the separation of acidic molecules through an ionic interaction with the basic quinine group, are also commonly used but in general they are classified with the anion-exchange type of chiral selectors (see further) because of their interaction mechanism, even though r-donor, r-acceptor properties occur. (Some separations on Pirkle-type CSPs are shown in Table 2.)... 

It would be of interest to see if our E and C parameters for the substituted phenol-base interactions can be transformed into Hammett ff and g parameters, i.e., to see how well the constraints of a Hammett treatment are adhered to by our E and C parameters derived from all types of donor-acceptor interactions. Unfortunately, the form of the... 

In the absence of electron donor-acceptor interactions, the London dispersive energy is the dominant contributor to the overall attractions of many molecules to their surroundings. Hence, understanding this type of intermolecular interaction and its dependency on chemical structure allows us to establish a baseline for chemical attractions. If molecules exhibit stronger attractions than expected from these interactions, then this implies the importance of other intermolecular forces. To see the superposition of these additional interactions and their effect on various partitioning phenomena below, we have to examine the role of dispersive forces in more detail,... 

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