Crotonaldehyde spectrum

Figure 6.15 The infrared vibrational spectrum of crotonaldehyde. The parts marked (a), (b) and (c) refer to a 10 per cent (by volume) solution in CCI4, a 1 per cent solution in CCI4, and a thin liquid film, respectively. [Reproduced, with permission, from Bowles, A. J., George, W. O. and Maddams, W. F J. Chem. Soc. (B), 810, 1969]...

F1= F1 F10 (s-lranx-crotonaldehyde) infrared spectmm, 159ff Raman spectrum, 159ff 14 9X (cyanotetraacetylene) interstellar, 120... 

The 13C spectrum of crotonaldehyde (CH3 CH=CH CHO Fig. 3.52) provides a good example of the way in which the 13C chemical shift is determined both by the state of hybridisation of the carbon atom and the nature of the substituent. The four carbon atoms have markedly different chemical shifts. The methyl carbon appears at 3 17.1. It is shifted downfield slightly compared to the methyl carbon at the end of a chain of methylene groups as in 3-methylheptane (Fig. 3.41) and hex-l-ene (Fig. 3.51). The two alkenyl carbons appear at <5133.4 and 3 152.9. The effect of conjugation of the carbon-carbon double bond is that the (i-carbon is shifted further downfield. The carbon of the carbonyl group is sp2-hybridised and is directly bonded to an electronegative atom. It is shifted furthest downfield and appears at 3 192.2,... 

Fig. 3.52 13C nuclear magnetic resonance spectrum of crotonaldehyde in CDClj sweep width 250 p.p.m. 

Fig. 3.72 Proton magnetic resonance spectrum of crotonaldehyde in CDC13, solution sweep offset 300 Hz, sweep width 500 Hz.

Fig. 3.73 Decoupled spectrum of crotonaldehyde. Data reproduced from W. McFarlane and R. F. M. White (1972). Techniques of High Resolution Nuclear Magnetic Resonance Spectroscopy. London Butterworths, p. 28.

Figures 3.72 and 3.73(a) and (b) illustrate the application of spin decoupling to the simplification of the spectrum of crotonaldehyde [(5) spectrum 3.72],...

Figure 6.17 The laser Raman vibrational spectrum of liquid crotonaldehyde. [Reproduced, with permission, from Durig, J. R., Brown, S. C., Kalasinsky, V. F. and George, W. O., Spectrochim. Acta, 32A, 807, 1976. Copyright 1976 Pergamon Press]...

The other compound, called Zl, which was much more acid-labile, was hydrolyzed to equimolar amounts of pyruvate and shikimate, and was tentatively assigned the structure of shikimate 3- or 5-enolpyruvate ether. In a more recent study, it was found that the barium salt of Zl does not absorb in the carbonyl region of the infrared absorption spectrum (no ester structure), and that it has a strong band at 8.2iu characteristic of a vinyl ether. It is oxidized very rapidly by periodate, giving rise to an unstable compound with maximum absorption at 235 m i ( = 4000). A similar unstable chromophore, most likely having the structure XVII, was produced by periodate oxidation of shikimate 3-phosphate but not of shikimate 5-phosphate. (3-Methyl-crotonaldehyde shows Xm 235, t = 6700. ) These observations suggest that Zl is shikimate 3-enolpyruvate ether (XVIII). 

Assign the various peaks in the H nmr spectrum of crotonaldehyde to specific protons in the molecule (Fig. 7). 

Load the configuration file ch54113.cfg an6 run the simulation of the 2D 130-1H relay COSY experiment of the crotonaldehyde type spin system. In this modified spin system the coupling between H-1 and H-2 is excluded to show the relay transfer from H-1 to H-2 trough C-1. Compare the result with the basic 1H COSY spectrum. Repeat both simulations using the spin system relcspsy.ham. Note however that in this spin system the 13C nucleus is 100% abundant. 

As shown in the list of relay COSY experiments heteronuclear correlation experiments are possible. In Check it 5.4.1.14 the H-H-X relay IR, DC COSY experiment for the crotonaldehyde type spin system is calculated. Implementing a relay step to a heteronucleus enables complex IR COSY spectrum to be disentangled by including a heteronuclear polarization transfer to link the IR signals to the heteronuclear chemical shift dimension. Fig. 5.26 illustrates this schematically for two spin systems. Since 8(Ra) = 5(Rd) and 5(Rt>) = 5(Rg) at least two IR, IR relay cross peaks which belong to two different relayed spin systems overlap in the IR, IR spectrum. Rowever because 5(Cc) 4 5(Cf) these peaks may be separated if the correlation peaks can be related to the heteronucleus which has a different chemical shift for each peak. 

A final point worth noting is that most steady-state spectrometers use Stark modulation. This modulation gives rise to Stark lobes, which are very helpful for assignments and dipole moment measurements. However, Stark lobes complicate the Zeeman spectrum and can lead to distortion of the Zeeman transitions and the baseline. The Fourier transform spectrometer eliminates this complication. The microwave molecular Zeeman effect in trans-crotonaldehyde has also been reported.16... 

FIGURE 2.37 The infrared spectrum of crotonaldehyde (neat liquid, KBr plates). 

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