Carboxylic acid derivatives spectra

The NMR spectrum of this compound shows a diamagnetic ring current of the type expected in an aromatic system. X-ray crystal structures of 1 and its carboxylic acid derivative 2 are shown in Fig. 9.2. Both reveal a pattern of bond lengths very similar to that in naphthalene (see p. 534). ... 

A number of nonnatural amino acids were resolved into individual enantiomers on 0-9-(2,6-diisopropylphenylcarbamoyl)quinine-based CSPby Peter and coworkers [48,90,113,114] after derivatization with Sanger s reagent, chloroformates (DNZ-Cl, FMOC-Cl, Z-Cl), Boc-anhydride, or acyl chlorides (DNB-Cl, Ac-Cl, Bz-Cl). For example, the four stereoisomers of P-methylphenylalanine, P-methyltyrosine, P-methyltryptophan, and P-methyl-l,2,3,4-tetrahydroisoquinoline-3-carboxylic acid could be conveniently resolved as various A-derivatives [113]. The applicability spectrum of cinchonan carbamate CSPs comprises also P-amino carboxylic acid derivatives, which were, for example, investigated by Peter et al. [114]. A common trend in terms of elution order of DNP-derivatized P-amino acids was obeyed in the latter study On the utilized quinine carbamate-based CSP, the elution order was S before R for 2-aminobutyric acid, while it was R before S for the 3-amino acids having branched R substituents such as wo-butyl, iec-butyl, tert-butyl, cyclohexyl, or phenyl residues. 

Valproic acid, valproate sodium, and (DVP) are carboxylic acid-derivative anticonvulsants. Divalproex sodium is a stable coordination compound consisting of valproic acid and valproate sodium in a 1 1 molar ratio (AHFS, 2000). It is a pro-drug of valproate, dissociating into valproate in the GI tract (AHFS, 2000), and a simple branched-chain carboxylic acid (w-dipropylacetic acid) with antiepileptic activity against a variety of types of seizures (Beydoun et al., 1997). Divalproex sodium has been approved for treating adults with simple and complex absence seizures (Mattson et al., 1992), and for mania. It has shown efficacy across a broad spectrum of BD subtypes (i.e., pure mania, mixed mania, and rapid cycling) (Pope et al., 1991 Bowden et al., 1994). 

The 2-carboxylic acid derivative had normal magnetic behaviour (ju = 1.81 BM at 295 K). A diffuse reflectance spectrum was characteristic of square planar complexes and an IR spectrum showed the presence of covalently bound carboxylate groups. 

With these compounds the presence of the halogen will have been detected in the tests for elements. Most acid halides undergo ready hydrolysis with water to give an acidic solution and the halide ion produced may be detected and confirmed with silver nitrate solution. The characteristic carbonyl adsorption at about 1800 cm -1 in the infrared spectrum will be apparent. Acid chlorides may be converted into esters as a confirmatory test to 1 ml of absolute ethanol in a dry test tube add 1 ml of the acid chloride dropwise (use a dropper pipette keep the mixture cool and note whether any hydrogen chloride gas is evolved). Pour into 2 ml of saturated salt solution and observe the formation of an upper layer of ester note the odour of the ester. Acid chlorides are normally characterised by direct conversion into carboxylic acid derivatives (e.g. substituted amides) or into the carboxylic acid if the latter is a solid (see Section 9.6.16, p. 1265). 

The simpler examples are readily hydrolysed in aqueous solution, and therefore react with sodium hydrogen carbonate and also give the ester test they may be confirmed by applying the hydroxamic ester test (Section 9.5.3, p. 1222). Carbonyl adsorption is apparent in the infrared spectrum at about 1820 cm-1 and at about 1760cm-1. It should be noted that aromatic anhydrides and higher aliphatic anhydrides are not readily hydrolysed with water and are therefore effectively neutral (Section 9.5.3, p. 1218). The final characterisation of the acid anhydride is achieved by conversion into a crystalline carboxylic acid derivative as for add halides. 

Different types of carbonyl groups give characteristic strong absorptions at different positions in the infrared spectrum. As a result, infrared spectroscopy is often the best method to detect and differentiate these carboxylic acid derivatives. Table 21-3 summarizes the characteristic IR absorptions of carbonyl functional groups. As in Chapter 12, we are using about 1710 cm-1 for simple ketones and acids as a standard for comparison. Appendix 2 gives a more complete table of characteristic IR frequencies. 

Hydrogens next to carbonyl groups absorb at around 2.1 8 in a H NMR spectrum, but this absorption can t be used to distinguish among carboxylic acid derivatives. 

Assigning the peaks to individual carbons in a C SSNMR experiment is not always trivial, as peaks can vary by more than 10 ppm from their solution values. In a broad sense, peaks from 160 to 180 ppm are due to carbonyl groups of carboxylic acid derivatives, 200-220 ppm are due to ketone carbonyls, 100-160 ppm are from aromatic and olefinic carbons, 50-100 ppm are from sp -hydridized carbons attached to heteroatoms, and 10-40 ppm are typically aliphatic carbons attached to other carbons and/or hydrogens. These are purely estimates of the basic functionalities found in most organic molecules, and exceptions to these ranges are not uncommon. Many crystalline systems also possess more than one crystallographically inequivalent molecule per unit cell, which is also easily detectable in SSNMR experiments and can make interpretation of spectra more complicated. For instance, if two peaks exist in the C SSNMR spectrum for each carbon, there are two molecules in the unit cell, although not every peak in each inequivalent molecule is always resolved. 

A review of the synthesis and chemistry of nitroxide spin labels includes a number of steroid derivatives. Novel spin-labelled steroids have been prepared by esterification with the nitroxyl carboxylic acid derivative (17),for use in spin immunoassays (SIA) as an alternative to radioactive labelling. The prednisolone ester (18), for example, exhibits an e.s.r. spectrum with narrow lines when it is in a free state in solution, but when bound to antibody the rate of tumbling is reduced, and linewidths are broad. Signals from bound and unbound derivatives are easily distinguished and measured, so SIA of antibody-bound prednisolone provides a potentially useful serum assay method. 

Isoxazolidine 1 itself exhibits strong peaks due to the ethylene and formaldoxime ion radicals.104 The mass spectrum of 5-methoxy-carbonyl-5-methylisoxazolidine has [R—C=0+) peak typical of carboxylic acid derivatives.104 For cycloserine (62), the initial fragmentation... 

The microwave spectrum of bicydo [2,1,0] pentane and six deuterium-labelled species has led to a complete structural analysis resulting in the parameters shown in (5) and an Y -ray analysis of the l-phenyl-exo-5-carboxylic acid derivative confirms the earlier n.m.r. assignments made by Schaffher. Gas-phase electron diffraction data on anti-tricyclo[3,l,0,0 ]hexanef show that the four-membered ring is planar with the three-membered rings canted out of the plane by 113°. 

Esters are carboxylic acid derivatives, and the spectrum of ethyl acetate is shown in Figure 14.19D. The carbonyl absorption does not distinguish this compound from an aldehyde or a ketone, but there is the C-O absorption at about 1200 cm 1. Because this is in the fingerprint region, however, its position can be difficult to identify. This is clearly the case for methyl pentanoate, where the C-0 absorption can easily be missed or misidentified. Based only on the infrared, it may be difficult to distinguish an ester from an aliphatic aldehyde or ketone. If the formula is known, however (from mass spectrometry), the identification is easier because an ester has two oxygen atoms, whereas the aldehyde or ketone has only one. 

The bicyclo[5,3,l]undec-7-ene-ll-one-l-carboxylic acid derivative (77) represents a case close to the limit for the possible existence of a bridgehead double bond. Unusual chemical and spectroscopic properties had suggested incomplete conjugation of the a -enone system, and this is confirmed by the analysis of (77) which reveals that the C(8)-C(7)-C(l l)-0 torsion angle is 37.6°. This value is in good agreement with the angle of 40° which had been predicted from an empirical examination of the u.v. spectrum. 

The signal for an aldehyde hydrogen typically appears between 8 9.5 and 8 10.1 in a H-NMR spectrum. Because almost nothing else absorbs in this region, it is very useful for identification. Hydrogens on an a-carbon (carbon directly adjacent to carbonyl) of an aldehyde or a ketone appear around 8 2.2 to 2.6. The carbonyl carbons of aldehydes and ketones have characteristic positions in the C-NMR between 8 180 and 8 215 (and can be distinguished from carboxylic acid derivatives, which absorb at a higher field). 

Recall that a carbonyl group produces a very strong signal between 1650 and 1850 cm in an IR spectrum. The precise location of the signal depends on the nature of the carbonyl group. Table 21.3 gives carbonyl stretching frequencies for each of the carboxylic acid derivatives. 

The carbonyl group of a carboxylic acid derivative generally appears in the region between 160 and 185 ppm, and it is very difficult to use the precise location of a signal to determine the type of carbonyl group present in an unknown compound. The carbon atom of a nitrile typically produces a signal between 115 and 130 ppm in a C NMR spectrum. 

CHAiUNCt Spectroscopic data for two carboxylic acid derivatives are given in NMR-A and NMR-B. Identify these compounds, which may contain C, H, O, N, Cl, and Br but no other elements, (a) H NMR spectrum A (one signal has been amplified to reveal all peaks in the multiplet). IR 1728 cm. High-resolution mass spectrum m/z for the molecular ion is 116.0837. 

Trihydroxypteridine exists predominantly in the dioxo-mono-hydroxy form 191(R = H), its ultraviolet spectrum closely resembling those of both the 1- and the 3-methyl derivatives and that of l,3-dimethyl-7-methoxypteridine-2,4-dione (191, R = Me). These spectra are quite different from those of 8-methyl- (192, R = H) and l,3,8-trimethyl-pteridine-2,4,7-trione (192, R = Me), which are similar to each other and to those of other 8-substituted pteridine-2,4,7-triones. However, the ultraviolet spectrum of 2,4,7-trihydroxypteri-dine does, indeed, show that a small proportion of the trioxo form is present at equilibrium. A somewhat larger proportion of the 6-methyl derivative exists in the trioxo form, although structure 193 predominates. The trioxo form (194) of 2,4,7 trihydroxy-l,3,6-trimethyl-pteridine is the most important tautomer, but the corresponding 6-carboxylic acid exists entirely in the monohydroxy-dioxo form 195. 

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