N electron donor

First examine the geometry of methyl radical. Is it planar or puckered Examine the geometries of 2-methy 1-2-propyl radical, trifluoromethyl radical, trichloromethyl radical and tricyanomethyl radical. Classify each of the substituents (methyl, fluoro, chloro and cyano) as a n-electron donor or as a Tt-electron acceptor (relative to hydrogen). Does replacement of the hydrogens by 7t-donor groups make the radical center more or less puckered Does replacement by Jt-acceptor groups make the radical center more or less puckered Justify your observations. 

The sterically unbiased dienes, 5,5-diarylcyclopentadienes 90, wherein one of the aryl groups is substituted with NO, Cl and NCCHj), were designed and synthesized by Halterman et al. [163] Diels-Alder cycloaddition with dimethyl acetylenedicarbo-xylate at reflux (81 °C) was studied syn addition (with respect to the substituted benzene) was favored in the case of the nitro group (90a, X = NO ) (syrr.anti = 68 32), whereas anti addition (with respect to the substituted benzene) is favored in the case of dimethylamino group (90b, X = N(CH3)2) (syn anti = 38 62). The facial preference is consistent with those observed in the hydride reduction of the relevant 2,2-diaryl-cyclopentanones 8 with sodium borohydride, and in dihydroxylation of 3,3-diarylcy-clopentenes 43 with osmium trioxide. In the present system, the interaction of the diene n orbital with the o bonds at the (3 positions (at the 5 position) is symmetry-forbidden. Thus, the major product results from approach of the dienophile from the face opposite the better n electron donor at the (3 positions, in a similar manner to spiro conjugation. Unsymmetrization of the diene % orbitals is inherent in 90, and this is consistent with the observed facial selectivities (91 for 90a 92 for 90b). 

When n electron donors are involved, the XB is preferentially along the axis of the donated lone pair on D. For instance, XBs around ethers, thioethers, and amines feature a tetrahedral arrangement with preferential axial directions for the XBs around hexacyclic amines, and equatorial directions for hexacyclic thioethers [16,17,124,139-142] (Fig. 6). 

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. 

In principle, aliphatic amines may interact as n electron donor molecules towards electron acceptor centres such as aromatic substrates, both homocyclic and heterocyclic, containing electron-withdrawing groups, usually nitro groups. These interactions are mainly electron donor-acceptor (EDA) interactions, in which aromatic amines are considered n or/and tt electron donors. 

The C—H bond is normally not very basic and will not interact with Lewis acids as a rule. However, in the presence of very powerful Lewis acids, such as carbocations, or if substituted by powerful n electron donors (X or C substituents), hydride abstraction from a carbon atom may be accomplished, corresponding to an oxidation of the C atom. 

Since the successful dehydrogenation of the organic ring moiety has been described recently,3,4 the five-membered heterocycle may deserve particular interest as potential precursor of a cyclic six n-electron donor ligand. 

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. 

The overlap and its consequences, as illustrated in Fig. 2.9, could equally well have been drawn with C—C bonds in place of the C H bonds. The energies of C C and C H orbitals are similar to each other, and the value of E will be similar. Alkyl groups in general are effectively n electron donors, in much the same way as, but to a lesser extent than, a double bond or a lone pair and we classify alkyl groups as X-substituents. 

If Y and A B are respectively an n-electron donor (D) and a sacrifical electron acceptor (A) as defined by Mulliken [47], then the Mulliken-type wavefunction of eq.(24)... 

Some experiments designed to obtain information about the nature of the catalytically active species have been carried out (15, 16), Complex formation between 7r-allylnickel halides and aluminum halides can be followed by the shift of the Trallyl protons in the H-NMR spectrum. By adding n electron donors, such as ethers or amines, the catalytically active complexes, XIII, are decomposed. 

Naphthalene (n - electron donor) and naphthylamine (la. -electron donor) were choosed as adsorbate molecules and spectral probes as well. There are several reasons for this choice ... 

In contrast to 2-chlorofuran, 2-fluorofuran so far is not known. Several theoretical works were devoted to the investigation of fluorine effect on the stability and reactivity of this compound.Furan ring is destabilized by n-electron donors and a-electron acceptors. These effects are more pronounced for substituents in 2- than 3-position of the ring. Fluorine substituent is known to be a strong a-electron acceptor and a 7i-electron donor at the same time and the introduction of fluorine in positions 2 and 3 affects significantly the stability of the furan ring. 

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