C Spectra

Chemical shifts for monohydroxy-steroids may be used additively to predict those for diols, except in cases where the two functional groups are in a 1,2-relationship or in certain 1,3-relationships. Steric interactions of hydroxy-groups in 1,2-gauche or 1,3-diaxial relationships are thought to explain some of the observed deviations from additivity, which closely resemble those asociated with 

Methyl substitution into ring A adjacent to an epoxide may cause an anomalous upheld shift of the C signal [e.g. of C-1 in a la-methyl-2,3-epoxide (15) or (16)]. 

The effect is discussed in terms of distortions of the normal half-chair conformation of the epoxycyclohexane ring, although the precise cause of the anomaly is not yet clear. The data serve as a warning for chemists using spectra for structural analysis of compounds with non-rigid conformations. 

Erroneous earlier assignments of C-15 and C-16 resonances in some pregnan-20-ones have been corrected. The new conclusions have allowed evaluation of substituent effects due to 17a-OH and 17a-Br groups. C N.m.r. spectroscopy has been applied in a study of the steroidal trisaccharides thevetin A and B, particularly the manner of linkage of the sugar units, leading to structures (17) and (18) respectively.  

C-P shifts are obscure, the other shifts are attributed to the electronic influence of the three-membered ring possessing carbon atoms with inverted tetrahedral geometry. 

Linear correlations between pK and the Hammett substituent constant a, and between chemical shifts of the carbonyl carbon atom and a, for the four isomeric norbornene acids of gross structure (42) are explained by a perturbation effect between the electric dipoles of the carboxy-group and R (R= H, Cl, NO2, or OMe). The preparation of C-enriched samples of 1-substituted butanes and adamantylmethyl derivatives (label at C-1 and the exocyclic carbon atom respectively) has enabled direct comparison of vicinal coupling constants. The uniformly smaller 

Spin-lattice relaxation time (T ) measurements have been employed in the charac-terizatioh of the resonances of paeoniflorin (43), a monoterpene bridgehead 0-p-glycoside isolated from the roots of Paeonia albiflora Pallas. In compounds 

Pulse sequences used to induce 1H-13C polarization transfer (PT), with suitably chosen delays (A) before data acquisition, provide a simple and reliable way of separating 13C resonances according to the number of attached protons.84 In an illustration for cholesterol, the seven CH carbons are displayed with A = (2J) 1 

Nihon Daigaku Kogakubu Kiyo Bunrui A, 1980, 21, 227. 

Steroidal and other rigid alcohols have been used to derive a four-parameter equation for the calculation of 13C chemical shifts due to substitution by the OH group.57 Calculated 13C chemical shifts for all the likely saturated sterol side-chains with from seven to eleven carbon atoms have been tabulated and compared, where possible, with published data.58 Good agreement is found in most cases, with standard deviations of ca. 1 p.p.m. Only C-20, attached to the steroid nucleus, showed serious deviations (ca. + 5 p.p.m.) from calculated values. The results will be useful in future structural assignments of new sterols. 

The aromatic ring of oestradiol or oestrone methyl ether readily forms a tricarbonyl chromium (0) complex in which the 13C signals from the aromatic ring are shifted strongly upheld (by ca. 14—34 p.p.m.). Smaller upheld shifts for other carbon atoms close to the aromatic ring (e.g. 2 p.p.m. for C-6) have been used to settle uncertainties in the earlier literature concerning the assignments of individual 18C resonances.69 13C N.m.r. spectra discriminate between A4- and A5-isomers of spiro-3-steroidal ketone derivatives thiazolidine formation results only in the (3i )-isomer (12), whereas hemithioacetals are mixtures of the (3R)- and (35)-forms.80 

The proton spectra of a range of chlorinated norbornenes are reported. The only 1 2 adduct formed from norbornadiene and cyclopentadiene is (21). The completely analysed spectrum shows the C-5 bridge protons at 51.53 because of steric deshielding which overcomes any shielding by the 7t-systems H-lOa appears at 1.17 and H-lOs at 1.28. The spectra of alkenes and ketones of the types (22) and (23) have also been analysed and conclusions drawn about the shielding effects of the double bonds.  

Casanova, B. Waegell, R. Grassend, and C. W. Jefford, Bull. Soc. chim. France, 1974. 2247. 

Paasivirta, M. Pitkanen, R. Laatikainen, and T. Kurkirinne, Finn. Chem. Letters, 1974, 215. 

Ueyama, T. Tsuji, H. Matsumura, H. Tanida, H. Iwamura, K. Kushida, T. Nishida, and S. 

Upfield shifts are observed in the C spectra of the y-carbon atoms in the antiperi-planar arrangement of X-C-C- C when X is N, O, or F as compared with C or H, except when X is located at the bridgehead of a bicyclic compound. Thus C-6 experiences greater shifts in the 2-exo-substituted norbornanes than in the 2-endo series of compounds, and a hyperconjugative tyi e interaction of free electron pairs is suggested. The deviations of observed shieldings from the values predicted by 

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WebSpectra includes 75 problems All the problems display the and C spectra several with DEPT or COSY enhancements A number include IR spectra Organic Structure Elucidation contains 64 problems all with and C NMR IR and mass spectra The exercises in both WebSpectra and Organic Structure Elucidation are graded according to difficulty Give them a try... 

Fig. 11. Micrographs of iastant films la cross section, swelled in 5% Na2S04 to reveal detail (lOOOX). Figures in parentheses indicate the approximate thickness of the swelled section relative to that of a nonsweUed section, (a) Polacolor ER (2.OX) (b) Fuji FP-lOO (1.5X) (c) Spectra film (1.3X). The sphere visible in (b) is a polymer bead of a type used in surface layers to prevent blocking.

A large amount of data are available on the C spectra of saturated six-membered ring systems. The subject has been reviewed in detail by Eliel and Pietrusziewicz (79MI20101). 

Figure 6. MAS NMR spectra of illite exchanged in 0.1 M NaCl solutions at 25°c. Spectra collected at = 11.7 T, room temperature, and room humidity ca. 35% RH).

In the decomposition of benzoyl peroxide, the fate of benzoyloxy radicals escaping from polarizing primary pairs remains something of a mystery. Benzoic acid is formed but shows no polarization in and C-spectra, and the carboxylic acid produced in other peroxide decompositions behaves similarly (Kaptein, 1971b Kaptein et al., 1972). Some light is shed on the problem by studies of the thermal decomposition of 4-chlorobenzoyl peroxide in hexachloroacetone containing iodine as... 

Gerhardinger, P. F., Flat-Glass Developments Reflect New Applications, / /zoto /c Spectra, pp. 104-105 (Jan. 1995)... 

Fig. 12. Effect of a strong exchange interaction on the shape of the EPR spectrum displayed by a pair of centers A and B having identical g vEilues, = 1.89, g, = 1.96, g = 2.07, and rotated magnetic axes according to xjly, yglx, zJIzy,. (a) 9 GHz spectrum calculated with J = 0 (b) and (c) spectra calculated with J = 25 X 10 cm at 9 and 35 GHz, respectively. The spectra were calculated as described in Ref. 192) without including any dipolar terms, with the linewidths ui = cr, = oi = 0.01.

The most widely used method for determining multiplicities of carbon atoms is DEPT (Distortionless Enhancement by Polarization Transfer). This has generally replaced the classical method of recording off-resonance C spectra with reduced CH couplings from which the multiplicity could be read directly. 

As stated earlier, since tt]/ = yff2yr and since the gyromagnetic ratio of proton is about fourfold greater than that of carbon, then if C is observed and H is irradiated (expressed as C H ), at the extreme narrowing limit Ti, = 198.8% i.e., the C signal appears with a threefold enhancement of intensity due to the nOe effect. This is a very useful feature. For instance, in noise-decoupled C spectra in which C-H couplings are removed, the C signals appear with enhanced intensities due to nOe effects. 

The conventional CP-MAS C spectra of hydrated onion cell walls can be seen in figure 2. This spectrum is derived from the low- and intermediate-mobility polymers present in the walls. 

By measuring the proton relaxation times, and T,p, it is possible to estimate the mobility of polymer chains within the cell wall (11). Proton spin relaxation editing (PSRE) is a method of expressing these results. It separates the components seen in a conventional CP-MAS C spectra into low-mobility and intermediate-mobility components. If PSRE is applied to a experiment (12) the mobility of the... 

Fig. 34.41. Dissimilarity of each spectrum with respect to (a) the mean spectrum, (b) spectrum at time 46 and (c) spectra at times 46 and 63, for the system of Fig. 34.40.

Fig. 42a-c Spectra of tetramethyltin in CDC13. a Proton decoupled, b proton coupled (2JsncH 54.3 Hz), c proton spectrum. The satellite signals are due to coupling to tin-117 (inner lines) and tin-119 (outer lines). The ratio of the coupling with tin-119 to that with tin-117 is 1.046 1 (the ratio of the magnetogyric ratios of the two nuclei)... 

For a start, we must be mindful of the fact that 13C is only present as 1.1 % of the total carbon content of any organic compound. This, in combination with an inherently less sensitive nucleus, means that signal to noise issues will always be a major consideration in the acquisition of 13C spectra - particularly 1-D13 C spectra which we will restrict the discussion to for the moment. (Note that the overall sensitivity of 13C, probe issues aside, is only about 0.28 % that of proton because the nucleus absorbs at a far lower frequency - in a 400 MHz instrument, 13C nuclei resonate at around 100 MHz.). So it takes a great deal longer to acquire 13 C spectra than it does proton spectra. More material is obviously an advantage but can in no way make up for a 350-fold inherent signal to noise deficiency ... 

C Spectra of CO adsorbed on CoZSM-5 before the contact with propene (a) and upon the formation and further decomposition. 

The strength of the Bronsted (BAS) and Lewis (LAS) acid sites of the pure and synthesized materials was measured by Fourier transformed infrared spectroscopy (ATI Mattson FTIR) by using pyridine as a probe molecule. Spectral bands at 1545 cm 1 and 1450 cm 1 were used to indentify BAS and LAS, respectively. Quantitative determination of BAS and LAS was calculated with the coefficients reported by Emeis [5], The measurements were performed by pressing the catalyst into self supported wafers. Thereafter, the cell with the catalyst wafer was outgassed and heated to 450°C for lh. Background spectra were recorded at 100°C. Pyridine was then adsorbed onto the catalyst for 30 min followed by desorption at 250, 350 and 450°C. Spectra were recorded at 100°C in between every temperature ramp. 

Fig. 2. Titration of 4.7 horseradish peroxidase (Curve A) with equimolar hydrogen peroxide to form HRP-compound I (Curve B), followed by addition of 7.0 pA/ vindoline (Curve C). Spectra were recorded every 15 sec. 

Fig. 3.81. HPLC analysis of reacted and unreacted RB4 (300 mg/1) total chromatogram at 598 nm (a and b), enlarged chromatogram from 27 to 28.5 min retention time (c), spectra of reacted RB4 componenets (d), and spectra of unreacted RB4 components (e) (DH, dihydrolysed MH, monohy-drolysed UH, unhydrolysed. Reprinted with permission from W. J. Epolito et al. [145].

Use a Flinn C-Spectra to view an incandescent lightbulb. What do you observe Draw the spectrum using colored pencils. 

Use the Flinn C-Spectra to view the emission spectra from tubes of gaseous hydrogen, neon, and mercury. Use colored pencils to make drawings in the data table of the spectra observed. 

With the room lights darkened, view the light using the Flinn C-Spectra . The top spectrum viewed will be a continuous spectrum of the white lightbulb. The bottom spectrum will be the absorption spectrum of the red solution. The black areas of the absorption spectrum represent the colors absorbed by the red food coloring in the solution. Use colored pencils to make a drawing in the data table of the absorption spectra you observed. 

NMR spectra were recorded on Bruker Digital FT-NMR Avance 400 spectrometer (CDClj solvent) with TMS as internal reference. In the C spectra qnatemaiy, methylene and methyl carbons were identified using DEPT experiments. IR spectra were recorded on Perkin Elmer FT-IR spectrometer (KBr). Reactions were performed under dry nitrogew Melting points were measured on a Gallenkamp melting point apparatus. Sihca gel 60 (Merck) was used for column separations. TLC was conducted on standart conversion aluminium sheets pre-coated with a 0.2 mm layer of sihca gel. 

Fig. 6.18. El mass spectra of ra-decane (a), 2,7-dimethyloctane (b), and 2,5,5-trimethyl-heptane (c). Spectra used by permission of NIST. NIST 2002.

Dubois et al. developed the Description, Acquisition, Retrieval, Computer-aided design-Elucidation by Progressive Intersection of Ordered Structures (DARC-EPIOS) system for structural elucidation.Their approach was based on C spectra. These were predicted using an additive method, but based on their DARC descriptor of environment, as opposed to the more common HOSE code. The EPIOS system was designed to take account of the diagnostic (or not) nature of the C spectrum with respect to environment, i.e., depending on the specific sub-structures. 

Figure 12.6 The effect of Savistky-Colay first and second derivative preprocessing on a set of NIR diffuse reflectance spectra (A) the raw (uncorrected) spectra, (B) spectra after Ist derivative preprocessing, (C) spectra after 2nd derivative preprocessing. In both cases the window width was 15 points (7.5 nm), and the polynomial order was 2.

In most C spectra, nuclei which have directly attached protons receive a significant (but not easily predictable) signal enhancement when the protons are decoupled as a result of the Nuclear Overhauser Effect (see Section 7.3) and as a consequence, peak intensity does not necessarily reflect the number of nuclei giving rise to the signal. 

It is not usually possible to integrate routine C spectra directly unless specific precautions have been taken. However with proper controls, NMR spectroscopy can be used quantitatively and it is a valuable technique for the analysis of mixtures. To record C NMR spectra where the relative signal intensity can be reliably determined, the spectra must be recorded with techniques to suppress the Nuclear Overhauser Effect and with a long delay between the acquisition of successive spectra to ensure that all of the carbons in the molecule are completely relaxed between spectral acquisitions. 

Fiqure 5. Absorption (a), fluorescence excitation (b) and fluorescence (c) spectra of compound 12 in EPIP at 77 K. Recording (b) and excitation (c) wavelengths are shown in brackets. Correction of exciting light spectral distribution for spectra c has been done up to 600 nm. 

Figure 1. Raman spectra of nickel-reconstituted hemoglobin (pH 7.5) obtained with 413.1-nm excitation (a), with 406.7-nm excitation (b), and the spectrum of nickel protoporphyrin IX free acid in cetyltrimethylammonium bromide micelles in 0.1 M NaOH (c). Spectra in (b) and (c) were obtained simultaneously on a Raman difference spectrometer.

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