Triads spectrum

The spectrum shown in Fig. 7.5 shows the appropriate portion of the spectrum for a copolymer prepared from a feedstock for which fj = 0.153 It turns out that each polyene produces a set of three bands The dyad is identified with the peaks at X = 298, 312, and 327 nm the triad, with X = 347 367, and 388 nm and the tetrad with X = 412 and 437 nm. Apparently one of the tetrad bands overlaps that of the triad and is not resolved. Likewise only one band (at 473 nm) is observed for the pentad. The identification ol these features can be confirmed with model compounds and the location and relative intensities of the peaks has been shown to be independent of copolymer composition. 

In a preliminary report (2), Fe atoms were reacted with O2, leading to formation of FeiO ), a cyclic isosceles (C2v) species, as suggested by mixed isotope experiments. Reaction of Fe atoms with N2O resulted in formation of FeO. A feature at 887 cm, assigned to a Fe/Nj complex, is probably erroneous, and may be an iron nitride species. In the same triad, the MCD spectrum of matrix-entrapped OSO4 was studied (46). The spectrum was found to be similar to that of Mn04 in a solid lattice, and was assigned accordingly. 

Example 2. Vinviidene Chloride Isobutylene Copolymer. The next example is for the carbon-13 spectrum of copolymer vinylidene chloride isobutylene. Figure 5 shows the full spectrum and the peak assignment listing for the non-protonated vinylidene chloride carbon in the 84-92 ppm range. Triad assignments were made (Crowther, M. W., 1987, Syracuse University, unpublished data) using the two-dimensional COLOC (20) experiment. There are ten v-centered pentads representing different environments for the vinylidene chloride carbon. The i represents the non-protonated carbon in the isobutylene polymer unit. 

The H-NMR spectrum of 2 in CDCI3 (Figure 1) exhibits broad unresolved resonances in the aromatic region similar to those found in the monomer. Broad signals with lack of resolution are consistent with magnetic non-equivalence of the methyl group protons resulting from a mixture of triad tacticities. 

Compositional sequences were assigned in the carbonyl region of the 3C spectra of poly(MAA/MMA) and in the 3 9Sn spectra of poly (TBTM/MMA). Both syndiotactic and heterotactic splittings were observed in the carbonyl spectrum. In the 9Sn spectrum only the syndiotactic compositional triad was observed. 

A UV-visible absorption spectrum of a 10 (J.M ethanol solution of a model compound (DAFc in Fig. 5) for the D moiety is shown together with that of the A-S-D triad in Fig. 16. The absorption bands between 200 and 300 nm can be clearly seen for DAFc. Qualitatively, absorption spectra for A-S-D triads in the LB films and in the 10 pM ethanol solution are similar. It is interesting to note, however, that the relative intensities of the acylated perylene band around 450 nm against the 200-300 nm UV absorption bands are different between the LB films and the ethanol solution. This difference can be attributed to orientation of the perylene moiety in the LB films in the same way as in the antenna LB films reported previously [38]. 

Unit distribution in the substituted PMMA (35) was investigated by two independant methods a) Direct analysis of copolymer microstructure by H-NHR at 250 MHz the NMR spectrum (pyridine solution at 80°C) are sufficiently well resolved to allow a quantitative analysis of unit distribution, in terms of A centered triads and isolated B units in ABA triads, b) UV studies of the ionization and of the intramolecular cyclization of the B B and B B dyads in protic basic media (Na0H-H 0 O.IN, NaOMe-MeOH O.IN) in such a medium the partially ionized copolymer chains are the site of a complex series of consecutive intramolecular reactions we have completely elucidated (35). The first step is of interest with respect to B unit distribution ... 

Figure 1 Differential absorption spectrum obtained upon nanosecond flash photolysis (532 nm) of 7.2 X 10M solutions of Fc-ZnP-H2P-C6o triad in nitrogen saturated benzonitrile with a time delay of 50 nsec at 298 K. (From Ref. 47.)...

There are only three unique triad combinations, mm, mr and rr thus a methyl configurational sensitivity to just nearest neighbor configurations would produce only three resonance in the methyl region of the C-13 spectrum. From an earlier spectrum of the amorphous polymer, we noted at least ten methyl resonances. We must therefore consider the situation where the next-nearest as well as nearest neighbor configurations are affecting the chemical shift, that is. 

To prove the correctness of this analysis we shall try to look for alternative explanations. A stereoregular heterotactic polymer. . . mrmrmr. . . could also explain the presence of a methyl singlet and a well-separated doublet of doublets for methylene protons, in agreement with the spectrum of the first sample in fact, there would be present the mr triad and the rmr tetrad with diastereotopic protons. However, in addition, an equal amount of the mrm tetrad should be present, yet the corresponding singlet is not visible with the required intensity. In the same way other hypothetical structures can be rejected. 

TPP)MnOAc (18) is an excellent initiator of the polymerization of the ringopening polymerization of PO. An example is illustrated in Fig. 52, where 400 equiv of PO was consumed completely in about 20 h at 30 °C. The NMR spectrum of the polymer shows a simple resonance pattern due to the CH3 group (6 17.4 ppm), indicating that the polymer consists exclusively of head-to-tail linkages. The NMR spectrum was also informative concerning the stereoregularity of the polyether, where the obtained polyether was almost atactic (i/s= 0.54 0.46,1/H/S=0.28/0.50/0.22). This is in contrast to the case with the aluminum porphyrin as initiator, which produces a polymer rich in isotactic triad sequences under similar conditions. 

The study of the stereoregularity of the polymers prepared, provides also Information about the stereoregulating mechanism. The probability of formation of the different types of sequences, was determined on the basis of the resonance of the quaternary carbon of pVP (12). The NMR spectrum performed at 15 MHz allows one to determine the concentration of triads. The values summarized In Table 4 do not agree with those expected for bernoullllan statistics. Hence, more than the last unit of the living chain Is Involved In the process. In order to obtain more precise Information about the process, It is necessary to measure the probability of formation of pentads. Such measurements are possible with spectra performed at 63 MHz (Figure 18). In spite... 

The 300 MHz H NMR and 20 MHz 13C NMR spectra of poly(4-methyl-l-pentene) have been found to be more complex than the corresponding spectra of poly(3-methyl-l-butene) due to the presence of an additional isomer structure in the polymer. Investigation of the 20 MHz 13C NMR spectrum of the polymer has indicated that placement of units in different triad sequences is die cause of multiple methyl proton resonances which have been observed in the H NMR spectra of poly(3-methyl-l-butene) and poly(4-methyl-l-pentene). The use of a computer program for simulating and plotting spectra has enabled measurements of polymer composition to be made of poly(4-methyl-l-pentene) s prepared under a variety of synthesis conditions. 

FIGURE 5. 62.8 MHz 13C NMR spectrum (olefinic region) of a 48% cis polymer of 1-methyl-norbomene. Catalyst Mo2(OAc)4/EtAlCl2. (HT + TH)/(HH + TT) = 2.8. The fine structure arises from double-bond triads, e.g. ccl, ccc, tct, tcc302. Reproduced by permission of the Society of Chemical Industry... 

Figure 5.21 29Si NMR spectrum of (PhSiMe) . The three principal fines have been associated with the triad arrangements, RM, RR and MM. Reprinted by permission from A. Wolff et al., J. Polym. Sci., Polym. Chem. Ed., 1988, 26, 713. Copyright 1988 John Wiley and Sons, Inc.

Triad 25 is another example of this general type [75]. As was the case with the previously discussed triads 15—18, the absorption spectrum of 25 indicates some degree of excitonic interaction between the porphyrins. The fluorescence quantum yield of 25 is 5 5 x 10-6, which indicates efficient quenching of the porphyrin singlet states, presumably by electron transfer. No information concerning the lifetime of any charge separated state was presented, but one would predict that it would be extremely short. 

---