1,3-Butadiene, absorption spectrum

The 7r — 77 transition for ethene has A.max =175 nm and emax = 10,000. It would be expected that an alkadiene would give an absorption spectrum similar to that of ethene but with a larger e, because there are more double bonds per mole to absorb radiation. This expectation is more or less realized for compounds such as 1,5-hexadiene and 1,3-dimethylenecyclobutane, which have isolated double bonds, but not for 1,3-butadiene or ethenylbenzene, which... 

A molecular ion-dominant spectrum has been observed for 2,3-dimethyl-1,3-butadiene (DB) excited with a 1.4-pm and 130 fs pulse, as shown in Fig. 2.5a, whereas many fragment ions were produced with a 0.8-pm femtosecond pulse of the same pulse width and intensity as shown in Fig. 2.5b. The cation absorption spectrum shown in Fig. 2.5c revealed that the non-resonant conditions hold with an excitation wavelength of 1.4 pm [4]. 

Fig. 2.5. TOF mass spectra of 2,3-dimethyl-l,3-butadiene (DB) are shown by a 1.4-p.m excitation at an irradiation intensity of 1.6 x 1014 W cm 2 and b 0.8 pm excitation at an irradiation intensity of 1.6 x 1014 W cm-2. Molecular ions are indicated by M+. The asterisk ( ) indicates H20+ signal, c The absorption spectrum of DB cation radical in a low-temperature matrix. The two shaded Gaussian shapes indicate the spectra of the excitation pulses...

Figure 3.4-3 a Infrared absorption spectrum of butadiene at a pressure of 107 mbar at room temperature, thickness 10 cm b infrared emission spectrum of the same sample at T = 800 K compared to the emission spectrum of a black body of 800 K, recorded with Lcitz prism spectrometer (Gutberlet, 1978). 

Resonance Raman spectra of 1,3-butadiene vapour have been observed with several laser lines between 239.5 and 165.7 A broad absorption spectrum due to the... 

Record the absorption spectrum between 400 and 200 nm of (a) 1-octene, (b) 1,3-butadiene, and (c) a nonconjugated diolefin (e.g., 1,4-pentadiene). What is the effect of a conjugated system on the absorption spectrum What does the spectmm tell you about the relative energy of the molecular orbitals in each compound ... 

Fig. 4. Calculated (a) and experimental (b) UV absorption spectrum of trans-butadiene, reproduced with permission from Ref. 58.

The resonance Raman spectrum of irans-butadiene at 217.9 mm has been computed in Ref. 58 by the TD approach, including the same dephasing time of 15 fs used for the absorption spectrum. Some details of the calculation have been presented in the Sec. 4.1.3 devoted to absorption spectra. In Fig. 9 the comparison between the theoretical and experimental results shows that nice agreements are now possible also for rather large molecules. The prominent role of the C=C stretching is evident, while the most important coupling mode (vg"), is not seen due to the dark nature of the 2 Ag state. The remaining lines are due to the fundamentals of the other in-plane modes (the out-of plane modes have not been considered) as well as some combination bands. 

The absorbance spectmm of 1,3-butadiene displays an absorption in the UV region (Xmax=217 nm), while the absorption spectrum of 1,2-butadiene does not display a similar absorption. Explain. 

Photochromic reactions in polymers also depend on the polarity of the polymer matrix. For example, when dispersed in or covalently attached to polymer matrices, the stability of polar merocyanine (MC) isomers in a polar matrix will be enhanced. Consequently, the reverse reaction rates in polar matrices will be reduced. Interactions between polar polymer matrices and photochromic l,3,3-trimethylindoline-6 -nitrobenzopyrylospiran (SP) molecules resulted in a blueshift of the absorption spectrum of SP. As shown in Figure 9.1, for the poly(n.-butyl methacrylate) (PnBMA) matrix with a lower Tg, larger blueshifts are observed compared to that of PMMA and styrene-butadiene-styrene (SBS) matrices. This behavior was attributed to polar and ionic interactions between PnBMA matrices and SP [27], the magnitude of these interactions though wiU vary depending upon the Tg of the matrix. 

During UV irradiation in air (oxygen) the absorption spectrum of styrene-butadiene rubbers (SBR) (Fig. 3.59) changes rapidly, in a way similar to that of polybutadiene (cf Fig. 3.58). This change is caused by carbonyl groups aliphatic (<300nm), aromatic or a,/ -unsaturated ketones and aldehydes (>300nm)p93]. 

Slade and Jonassen (192) treated ethyleneplatinous chloride, [Pt2Cl4-(C2H4)2], with butadiene, and obtained an unstable complex to which they ascribed the chlorine-bridged structure (XXXIV), on the evidence that its infrared spectrum showed a weak absorption at 1608 cm-1 due to the free double bond of each butadiene molecule. 

In the case of butadienic lipids, the polyreaction was followed by a decrease of the strong monomer absorption (260 nni)25). Disappearance of vinyl protons in the 2H NMR spectrum proved polymer formation for vesicles made from vinylic, acryloylic, and methacryloylic surfactants l3,16). 

UV spectra lack detail. Samples must be extremely pure or the spectrum is obscured. To the right is a UV spectrum of 2-mcthyl-1,3-butadiene dissolved in methanol. The methyl group increases the absorption wavelength slightly. The methanol solvent makes no contribution to the spectrum. Spcetra are typically not printed, but instead given as lists. The spectrum to the right would be listed as ... 

Fig. 4. C-NMR spectrum of complex, n-BuLi-DPE and 1,3 butadiene. Note absorption peaks between 140 and 146 ppm assigned to ir-complexes of Bd and n-BuLi-DPE.

The determination of percentage of styrene and butadiene isomer distribution in copolymers is an extension of the methods for the analysis of polybutadiene. The styrene band at 700 cm 1 is largely independent of the sequence distribution and therefore useful in styrene content determination [76]. A series of bands in the IR spectrum of crystalline isotactic polystyrene at 758, 783, 898, 920, 1053, 1084, 1194, 1261, 1297, 1312 cm"1 have been attributed to the helical structure [77]. The absorption bands for butadiene in SBR are similar to BR structures (Table 3.2a). 

---