1,3-Butadiene absorption

These compounds show typical s+rans-1,3-butadiene absorption bands between 230 and 235 nm, with emax 30000. In correspondence, the CD spectra show an intense (Ae 3-5) Cotton effect, positive for the (S) absolute configuration of the chiral centres. It is noteworthy that if one considered (E)-(S)-6 as a half of (E, E)-(3S,8S)-7 a value of Ae of about 0.4 would be predicted the actual Ae of +3 is one order of magnitude larger ... 

Figure 2. Butadiene absorption-desorption by 0,25M cyano-cobaltate(ll)...

Figure 2.9 Occupation of energy levels in butadiene. Absorption of electromagnetic raeSation causes promotion of an electron from the n = 2 to the n = 3 level...

Linear polyenes (butadiene, hexatriene, etc.) absorb ultraviolet radiation. They have absorption maxima at the approximate wavelengths given in Table 6-1. 

Another use is in various extraction and absorption processes for the purification of acetylene or butadiene and for separation of aHphatic hydrocarbons, which have limited solubiHty in DMF, from aromatic hydrocarbons. DMF has also been used to recover CO2 from flue gases. Because of the high solubiHty of SO2 iu DMF, this method can even be used for exhaust streams from processes using high sulfur fuels. The CO2 is not contaminated with sulfur-containing impurities, which are recovered from the DMF in a separate step (29). 

Most rubbers used in adhesives are not resistant to oxidation. Because the degree of unsaturation present in the polymer backbone of natural rubber, styrene-butadiene rubber, nitrile rubber and polychloroprene rubber, they can easily react with oxygen. Butyl rubber, however, possesses small degree of unsaturation and is quite resistant to oxidation. The effects of oxidation in rubber base adhesives after some years of service life can be assessed using FTIR spectroscopy. The ratio of the intensities of the absorption bands at 1740 cm" (carbonyl group) and at 2900 cm" (carbon-hydrogen bonds) significantly increases when the elastomer has been oxidized [50]. 

Other nylons are made by varying the molecular length of the diamines and the dibasic acids Nylon-fi. in u.ses sebacic acid (10 carbon atoms), nylon-11 uses an acid from castor oil, and nylon-12 uses butadiene. These variations decrease moisture absorption. Other variations use amines with a ring structure, e.g., the aromatic nylons to give polymers with softening points above 577 F,... 

Polystyrene One of the high volume plastics, is relatively low in cost, easy to process, has sparkling clarity, and low water absorption. But basic form (crystal PS) is brittle, with low heat and chemical resistance, poor weather resistance. High impact polystyrene is made with butadiene modifiers provides significant improvements in impact strength and elongation over crystal polystyrene, accompanied by a loss of transparency and little other property improvement. PS is used in many different formulations. 

Chemical methods for structure determination in diene pol3 mers have in large measure been superseded by infrared absorption techniques. By comparing the infrared absorption spectra of polybutadiene and of the olefins chosen as models whose ethylenic structures correspond to the respective structural units, it has been possible to show that the bands occurring at 910.5, 966.5, and 724 cm. are characteristic of the 1,2, the mns-1,4, and the m-1,4 units, respectively. Moreover, the proportion of each unit may be determined within 1 or 2 percent from measurements of the absorption intensity in each band. The extinction coefficients characteristic of each structure must, of course, be known these may be assigned from intensity measurements on model compounds. Since the proportions of the various units depend on the rates of competitive reactions, their percentages may be expected to vary with the polymerization temperature. The 1,2 unit occurs to the extent of 18 to 22 percent of the total, almost independent of the temperature, in free-radical-polymerized (emulsion or mass) poly butadiene. The ratio of trans-1,4 to cfs-1,4, however,... 

Many common polymers, polymeric additives and lubricants oxidise so rapidly after impact in liquid oxygen that they are hazardous. Of those tested, only acrylonitrile-butadiene, poly(cyanoethylsiloxane), poly(dimethylsiloxane) and polystyrene exploded after impact of 6.8-95 J intensity (5-70 ft.lbf). All plasticisers (except dibutyl sebacate) and antioxidants examined were very reactive. A theoretical treatment of rates of energy absorption and transfer is included [1], Previously, many resins and lubricants had been examined similarly, and 35 were found acceptable in liquid oxygen systems [2],... 

Absorption by ladder polysilanes, 143-144, 148-149, 150-151 Acetylation of thiobetaines, 63-64 Acids see Lewis acids Addition elimination in butadiene cyclo-oligomerization, 170 Addition reactions... 

This is the most populated form of 1,3-butadiene, which at room temperature is present in about 99% abundance5,6. The characteristic absorption feature of this chromophore is the intense band at about 210 nm showing emax larger than 20000. It has been unanimously6 assigned to the r - jt L(lAg - 1BU) transition of the C2h chromophore (see Appendix, Section V). 

To illustrate the latter point, consider the butadiene radical cation (BD+ ). On the basis of Hiickel theory (or any single-determinant Hartree-Fock model) one would expect this cation to show two closely spaced absorption bands of very similar intensity, due to 7i i -> ji2 and ji2 —> JI3 excitation (denoted by subscripts a and v in Figure 28), which are associated with transition moments /xa and /xv of similar magnitude and orientation. Using the approximation fiwm) —3 eV288 the expected spacing amounts to about 0.7 eV. 

Shida and Hamill23 found that the positive and negative molecular ions of 1,3-butadiene and its homologs have similar absorption spectra. Band maxima of the anions are not sensitive to substituent alkyl groups, whereas those of the cations are red-shifted as the number of substituent methyl groups increases. In alcoholic matrices the butadiene anions abstract the alcoholic proton to form an allylic radical (equation 23), as was proven by ESR spectroscopy. 

It is evident that the s-cis frozen conformation in the ring of 2 shows a batochromic shift, but a much lower absorption (s) in comparison with butadiene (1). Woodward and... 

Absorption bands due to conjugated chromophores are shifted to longer wavelengths bathochromic or red shift) and intensified relative to an isolated chromophore. The shift can be explained in terms of interaction or delocalization of the 7t and % orbitals of each chromophore to produce new orbitals in which the highest ti orbital and the lowest k orbital are closer in energy. Figure 9.8 shows the conjugation of two ethylene chromophores to form 1,3-butadiene. The n—>n transition in ethylene occurs at 165 nm with an s value of 1500 whereas in 1,3-butadiene the values are 217 nm and 2100 respectively. 

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