N-electron acceptor

Small chiral molecules. These CSPs were introduced by Pirkle about two decades ago [31, 32], The original brush -phases included selectors that contained a chiral amino acid moiety carrying aromatic n-electron acceptor or n-electron donor functionality attached to porous silica beads. In addition to the amino acids, a large variety of other chiral scaffolds such as 1,2-disubstituted cyclohexanes [33] and cinchona alkaloids [34] have also been used for the preparation of various brush CSPs. 

As discussed above, monomer molecules are capable of functioning either as it-electron donors and n-electron acceptors (e.g. C=C double bond containing compounds), respectively, or as n-electron donors (e.g. epoxides). Therefore, their ground or excited states can interact with donor or acceptor molecules, which are unable to polymerize. For that interaction the general Scheme 3 holds, too. Clearly, in these cases only a homopolymerization of the monomer used takes place. The mechanism of that reaction depends on the electronic properties existing (e.g. monomer acts as donor or acceptor), and on the structural conditions in both molecules. Again, in some cases a proton transfer reaction could occur. 

Most alkyl carbanions undergo facile pyramidal inversion. Cyclopropyl anions are an exception, presumably because the transition state, with a planar trigonal carbon, is more strained than the ground state. The configurational stability of cyclopropyl anions is of value in the synthesis of deuterated cyclopropanes by the Haller-Bauer reaction (see Section II.B). An interesting dilemma arises when a cyclopropyl anion is stabilized by a n-electron acceptor substituent such as a nitrile or an ester. Will the anion then retain its pyramidal equilibrium geometry for the strain reasons alluded to above, or will it become planar in order to maximize overlap of the filled orbital on carbon with the n orbital of the substituent Walborsky and coworkers addressed this question in a series of experiments in which rates of H/D exchange and racemization were compared for an optically active cyclopropane exposed to a base in a deuterated hydroxylic solvent. The outcome can be illustrated with the particular example of 1,1-diphenylcyclopropane-2-... 

Heterocyclic n-electron acceptor Polarizable n-electron Bridge Heterocyclic n-electron acceptor... 

Hi) n-electron acceptor/yc-electron donor stationary phases l-(3,5-Dinitrobenzamido)-l,2,3,4-tetrahydrophenanthrene W-(3,5-Dinitrobenzoyl)-l,2-diphenyl-1.2-diaminoethane yV-(3,5-Dinitrobenzoyl)-l,2-diaminocyclohexane yV-(3,5-DinitrobenzoyI)-(l-naphthyl)glycine amide Whelk-O 1 ULMO DACH DNB CHIREX 3005... 

A recent compilation [306] contains Gp, and the redefined and values of 530 substituents, together with Gp,Op, M values (eq. 44, values of 7i-electron donor substituents eq. 45, 3 values of n-electron acceptor substituents), and values (eq. 46, values of 7t-electron donor substituents) of 223 substituents as well as some other electronic parameters derived from spectroscopic data as compared to normal values, the and values of 7t-electron donor... 

The P values for the unsaturated ligands of our study, usually at ReCI(dppe)2, have been estimated by using eq.7 or derived ones, the measured or Ep/2° values (the Isriter for the irreversible anodic processes), and the knowledge [3] of Eg (0.68 V) and p (3.4) for this centre. This has allowed to order them as follows (with the P values in parentheses), according to their net n-electron acceptor / a-donor character ... 

Fukiizinm S, Kajima T (2008) Photofimctional nanomaterials composed of multiporphyrins and carbon-based n-electron acceptors. J Mater Chem 18 1427—1439... 

After the photoinduced switching process, back switching should be easily effected by allowing O2 to enter the irradiated solution. The reduction of n-electron acceptors (bipyridinium-type systems) is easy and reversible, whereas oxidation of Ji-electron donors (aryloxy-type systems) is difficult and often irreversible. Thus, it is more convenient to use systems which contain the n-electron acceptor in the dumbbell component and the jt-electron donor in the ring component. 

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