Liquid state spectrum

Figure 9.23. A. N NMR spectra of polyborazilene precursor for the production of BN. Upper solid state MAS spectrum, middle solid-state CP MAS spectrum, lower liquid-state spectrum in tetrahydrofuran. B. Schematic representations and calculated N chemical shifts of the various environments in hexagonal BN. C. Observed and simulated N MAS NMR spectrum of polyborazilene showing the fitted components with assignments according to the environments of Figure 9.23B. The fitted peaks from the BHN2 sites are shown by full lines, those from BN3 sites by broken lines. From Gervais et al. (2001), by permission of the American Chemical Society.

Figure 27 (A) Liquid-state ID spectrum of precursor dissoived in CD2CI2 and ID MAS spectra of (B) solid precursor and (C) GNR. The solid-state precursor spectrum shows relatively narrow lines indicating a flexible structure, whereas the broad resonance-shifted spectrum of GNR indicates the presence of an extended inhomogeneous packed -conjugated system. The 2D H- H DQ-SQ correlation spectra of (D) precursor and (E) GNR probe internuclear spatial proximities. The assignment scheme is seen in (F). The liquid-state spectrum was acquired at 7 T and the solid-state spectra were acquired at 16.45 T using 59,524 Hz MAS. Adapted with permission from Ref. [236]. Copyright 2014 Macmillan Publishers Limited.

The solid-state spectrum of diglycidyl ether of bisphenol-A (DGEBA) has been compared with the liquid-state spectrum [9], and the chemical shifts were examined using the steric-hindrance model. This model has also given consistent results in the analysis of chemical shifts of the a and conformers of tran5-l,4-polyisoprene in the solid state [10]. The sterie-hindrance model prediets shifts that are the same order of magnitude as those observed. 

This chapter simnnarizes the interactions that affect the spectrum, describes the type of equipment needed and the perfomiance that is required for specific experiments. As well as describing the basic experiments used in solid-state NMR, and the more advanced teclmiques used for distance measurement and correlation, some emphasis is given to nuclei with spin / > dsince the study of these is most different from liquid-state NMR. 

Until 1962 the infrared and Raman spectra of thiazole in the liquid state were described by some authors (173, pp. 194-200) with only fragmentary assignments. At that date Chouteau et al. (201) published the first tentative interpretation of the whole infrared spectrum between 4000 and 650 cm for thiazole and some alkyl and haloderivatlves. They proposed a complete assignment of the normal modes of vibration of the molecule. 

Figure 9.18 shows a typical energy level diagram of a dye molecule including the lowest electronic states Sq, and S2 in the singlet manifold and and T2 in the triplet manifold. Associated with each of these states are vibrational and rotational sub-levels broadened to such an extent in the liquid that they form a continuum. As a result the absorption spectrum, such as that in Figure 9.17, is typical of a liquid phase spectrum showing almost no structure within the band system. 

It is curious that the chair- boat problem, which is most associated with small, liquid-state molecules, arises in the context of solid-state research (B3, II). Although the paucity of useful experiments militates against a definitive solution here E3), the frequency independence of the NMR second moment (E2), the absence of an observable free-induc-tion decay (Tj <25 fis) in the pulsed NMR spectrum (El), and the smoothness of the absorption mode itself (SI), all argue against the... 

FIGURE 10.6 Comparison of solid-state and liquid-state spectra from a copper protein. The figure illustrates shifts in apparent gz and Az-values of the S = 1/2 and I =3/2 spectrum from Cu11 in bovine superoxide dismutase as a function of the surrounding medium. Top trace frozen aqueous solution at 60 K middle trace frozen water/glycerol (90/10) solution at 60 K bottom trace aqueous solution at room temperature. (Modified from Hagen 1981.)... 

The Raman spectrum of valproic acid as shown in Figure 8, was obtained in the undiluted liquid state on a Cary Model 83 Spectrometer. The following bands (cm l) have been assigned for Figure... 

Figure 13.4 Ordinary Raman spectrum of BZI (benzyl isocyanide) in (a) neat liquid state, and SERS spectra of (b) 5 X 10 M BZI in aqueous Ag nanocolloids, and (c)...

Figure 1. Three stages of resolution in a C-I3 spectrum of a cured epoxy. The top spectrum is obtained under conditions appropriate to a liquid-state spectrometer no dipolar decoupling and no magic angle spinning. Dipolar decoupling at 60 kHz is used for the middle spectrum and to that is added magic angle rotation at 2.2 kHz for the bottom figure.

FIGURE 3.3. Infrared spectrum of cyclopentanone in various media. A. Carbon tetrachloride solution (0.15 M). B. Carbon disulfide solution (0.023 M). C. Chloroform solution (0.025 M). D. Liquid state (thin films). (Computed spectral slit width 2 cm-1.)... 

Narrow absorption lines can be observed in the liquid state only when the relaxation processes do not produce small values for Tv Thus the resonance of Ti(H20)6+ is not seen because the octahedral symmetry gives orbital states close to the ground state and this in turn leads to short 7Vs and hence broad absorption lines. When fluoride ions are added to produce a complex of low symmetry (23) in which there are no excited states close to the ground state, the ESR spectrum is observed as a narrow line. 

The Si liquid state NMR spectrum of experiment 11 (Figure lb) displays mainly one sharp and intense line at -99.4ppm corresponding to the D4R units. It is worthy to note that in the presence of a large amount of sodium cations (experiment 4), the concentration of D4R species considerably decreases (see Figure lc), such a result being already mentioned in the literature [15]. 

In summary, theoretical considerations show that the Hamiltonian operator responsible for the central part of the spectrum when line-narrowing techniques are applied is almost identical to that effective in the liquid state. 

There are many experiments which determine only specific frequency components of the power spectra. For example, a measurement of the diffusion coefficient yields the zero frequency component of the power spectrum of the velocity autocorrelation function. Likewise, all other static coefficients are related to autocorrelation functions through the zero frequency component of the corresponding power spectra. On the other hand, measurements or relaxation times of molecular internal degrees of freedom provide information about finite frequency components of power spectra. For example, vibrational and nuclear spin relaxation times yield finite frequency components of power spectra which in the former case is the vibrational resonance frequency,28,29 and in the latter case is the Larmour precessional frequency.8 Experiments which probe a range of frequencies contribute much more to our understanding of the dynamics and structure of the liquid state than those which probe single frequency components. 

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