Donor-acceptor properties

The contribution of this polar structure to the bonding lowers the energy of the transition state. This may be viewed as a lower activation energy for the addition step and thus a factor which promotes this particular reaction. The effect is clearly larger the greater the difference in the donor-acceptor properties of X and Y. The transition state for the successive addition of the same monomer (whether X or Y substituted) is structure [V] ... 

Table 7.4 lists the Q and e values for an assortment of common monomers. The extremes in the column of e values in Table 7.4—which are listed in order-quantify the range of donor-acceptor properties which is used as the basis for ranking in Fig. 7.2. The Q values perform a similar ranking with respect to resonance effects. The eight different Q-e combinations in Table 7.4 allow the estimation of ri and values for 28 different copolymers. Of course, in these systems Q and e values were assigned to give the best fit to r values which had already been measured. As an illustration of the predictive values of the Q-e scheme, consider the following example ... 

IV. DONOR-ACCEPTOR PROPERTIES OF SULFONES AND SULFOXIDES IN PHOTOCHEMISTRY... 

Random copolymerization occnrs between butadiene and styrene [15]. There are no appreciable differences in the nncleophilic and electrophilic abilities between the radical centers with the vinyl and phenyl groups at the end of the growing polymer chain or in the donor/acceptor properties between the monomers. 

The kinetic stabilities and the donor-acceptor properties of cyclic conjugated molecules [68] have been described (Scheme 12) in the theoretical subsection (Sect. 2.2.2) to be controlled by the phase property. There is a parallelism between the thermodynamic and kinetic stabilities. An aromatic molecule, benzene, is kinetically stable, and an antiaromatic molecule, cyclobutadiene, is kinetically unstable (Scheme 13). 

According to the theory of cyclic conjugation, the Hueckel rule is applicable only to a continuous cyclic conjugation, but not to a discontinuous one (Schemes 14 and 15). In the discontinuously conjugated molecules, electron donors and acceptors are alternately disposed along the cyclic chain [25].The thermodynamic stability depends neither on the number of n electrons nor the orbital phase properties, but on the number of neighboring donor-acceptor pairs. Chemical consequences of the continuity-discontinuity of cyclic conjugation are reviewed briefly here. 

Fig. 8. Examples of some of the donor-acceptor substituted TEEs prepared for the exploration of structure-property relationships in the second- and third-order nonlinear optical effects of fully two-dimensionally-conjugated chromophores. For all compounds, the second hyperpolarizability y [10 esu], measured by third harmonic generation experiments in CHCI3 solution at a laser frequency of either A = 1.9 or 2.1 (second value if shown) pm is given in parentheses. n.o. not obtained...

The force constants of the Ni—P bond in P " nickel carbonyl complexes increase in the order MeaP < PHg < P(OMe)a < PFs. This order is different from that of the donor-acceptor character, as estimated from uco-The lengthening of the P—O bond of triphenylphosphine oxide upon complexation with uranium oxide has been estimated by i.r. spectroscopy. However, A -ray diffraction shows little difference in the P-O bond lengths (see Section 7). Some SCF-MO calculations on the donor-acceptor properties of McaPO and H3PO have been reported. 

Yatsimirskii, K. (1970). Acid-base and donor-acceptor properties of ions and molecules. Theoretical and Experimental Chemistry (USSR), 6, 376-80. 

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