Carbonyl compounds spectroscopy

Paal-Knorr synthesis, 4, 118, 329 Pariser-Parr-Pople approach, 4, 157 PE spectroscopy, 4, 24, 188-189 photoaddition reactions with aliphatic aldehydes and ketones, 4, 232 photochemical reactions, 4, 67, 201-205 with aliphatic carbonyl compounds, 4, 268 with dimethyl acetylenedicarboxylate, 4, 268 Piloty synthesis, 4, 345 Piloty-Robinson synthesis, 4, 110-111 polymers, 273-274, 295, 301, 302 applications, 4, 376 polymethylation, 4, 224 N-protected, 4, 238 palladation, 4, 83 protonation, 4, 46, 47, 206 pyridazine synthesis from, 3, 52 pyridine complexes NMR, 4, 165... 

Chiral salen chromium and cobalt complexes have been shown by Jacobsen et al. to catalyze an enantioselective cycloaddition reaction of carbonyl compounds with dienes [22]. The cycloaddition reaction of different aldehydes 1 containing aromatic, aliphatic, and conjugated substituents with Danishefsky s diene 2a catalyzed by the chiral salen-chromium(III) complexes 14a,b proceeds in up to 98% yield and with moderate to high ee (Scheme 4.14). It was found that the presence of oven-dried powdered 4 A molecular sieves led to increased yield and enantioselectivity. The lowest ee (62% ee, catalyst 14b) was obtained for hexanal and the highest (93% ee, catalyst 14a) was obtained for cyclohexyl aldehyde. The mechanism of the cycloaddition reaction was investigated in terms of a traditional cycloaddition, or formation of the cycloaddition product via a Mukaiyama aldol-reaction path. In the presence of the chiral salen-chromium(III) catalyst system NMR spectroscopy of the crude reaction mixture of the reaction of benzaldehyde with Danishefsky s diene revealed the exclusive presence of the cycloaddition-pathway product. The Mukaiyama aldol condensation product was prepared independently and subjected to the conditions of the chiral salen-chromium(III)-catalyzed reactions. No detectable cycloaddition product could be observed. These results point towards a [2-i-4]-cydoaddition mechanism. 

Infrared spectroscopy—cont d carbonyl compounds. 428-429 carboxylic add derivatives,... 

Infrared spectroscopy 10 ng ml-1 Suitable for carbonyl compounds NaCl, CaF2 and sapphire cells are available... 

Reduction of the nicotinoyl group with dithionite at pH 7 was followed by both NMR and UV/vis spectroscopy. This analysis showed that the lifetime of the generated dihydropyridine group had been extended relative to 1-methyl-nicotinamide by more than a factor of 3. This system has not yet been shown to be capable of supporting nicotinamide-catalyzed reduction of carbonyl compounds however, the successful inclusion of this functionality within a stable... 

For instance, Kochi and co-workers [89,90] reported the photochemical coupling of various stilbenes and chloranil by specific charge-transfer activation of the precursor donor-acceptor complex (EDA) to form rrans-oxetanes selectively. The primary reaction intermediate is the singlet radical ion pair as revealed by time-resolved spectroscopy and thus establishing the electron-transfer pathway for this typical Paterno-Biichi reaction. This radical ion pair either collapses to a 1,4-biradical species or yields the original EDA complex after back-electron transfer. Because the alternative cycloaddition via specific activation of the carbonyl compound yields the same oxetane regioisomers in identical molar ratios, it can be concluded that a common electron-transfer mechanism is applicable (Scheme 53) [89,90]. 

Reactions of carbonyl compounds such as pyridine 2-carboxaldehyde, glyoxal, biacetyl, or benzil with 2-aminothiophenol on an Fe + template give benzothiazolinate (198) complexes. The complex from pyridine 2-carboxaldehyde, for example, was formulated, on the basis of NMR and Mossbauer spectroscopy and of analysis (C, H, N, and Fe) as the bis-(A,iS)-ligand-bis-aqua complexes of (199), an isomeric form in equilibrium with (198). However as they are diamagnetic it seems more likely that they are [Fe(199)2] 2H20, containing terdentate (N,N,S) (199), than the proposed [Fe(199)2(H20)2]. 

Radical-anions can be characterised by esr-spectroscopy. Those derived from simple carbonyl compounds such as acetone or 3-methylbutan-2-one are highly reactive and can only be detected in a glassy matrix prepared by the alternate d o-sition of layers of sodium and the ketone at 77 K [4], lire radical-anion from the... 

The most important application of organolithium reagents is their nucleophilic addition to carbonyl compounds. One of the simplest cases would be the reaction with the molecule CO itself, whose products are stable at room temperature. Recently, it was shown that a variety of RLi species are able to react with CO or f-BuNC in a newly developed liquid xenon (LXe) cell . LXe was used as reaction medium because it suppresses electron-transfer reactions, which are known to complicate the reaction . In this way the carbonyllithium and acyllithium compounds, as well as the corresponding isolobal isonitrile products, could be characterised by IR spectroscopy for the first time. 

MetaUation of 4-hetero-substituted dibenzothiins (427) with lithium, catalyzed by 4,4 -di-f-butylbiphenyl (equation 122), breaks one of the C—S bonds. Quenching with carbonyl compounds leads to the corresponding thiophenols (428) that may be cyclized to the homologous seven-membered heterocycles (429). The products can be characterized by IR, H and NMR spectroscopies and MS . ... 

Reaction of (159) with other carbonyl compounds was monitored by H NMR spectroscopy <90JHC1993>. Acetophenone and benzophenone in CDCI3 at 60 °C gave within 2 h a small amount of (179) analogues but mainly thermal decomposition products of the latter. Benzaldehyde reacts at room temperature but the resulting analogue (179) decomposes completely. 

The conditions for the photocycloaddition (discussed in detail in a later section of this review) can be relatively mild. There is usually a small probability of the oxetane being destroyed in dark reactions which would probably preclude isolation after preparation by any method. One mode of decomposition of oxetanes is fragmentation, either back to the starting materials or to the other possible carbonyl compound and olefin. For example, the oxetane from 4,4 -dimethoxybenzophenone and isobutylene forms readily and is easily detected and characterized by infrared and NMR spectroscopy. All efforts to purify it, however, have led to its decomposition into formaldehyde and the diarylethy-lene.17 37 In some cases, as with fluorenone and isobutylene37 or 2-methyl-2-butene,25b the oxetane is apparently too unstable for detection, but the presence of the olefin 96 attests to its formation. 

The starting oximes (acetophenone oxime and cyclohexanone oxime) were prepared by reaction of the corresponding carbonyl compound with hydroxylamine hydrochloride. The purity of the resulting oximes was checked by GC and IR spectroscopy after recrystallisation of the samples. 

It is commonly accepted that chemisorption of CO on transition metals takes place in a way that is quite similar to bond formation in metal carbonyls (4). First experimental evidence for this assumption was obtained from a comparison of the C—O stretching frequencies (5) and was later confirmed by data on the bond strength (6) as well as by valence and core level ionization potentials obtained by photoelectron spectroscopy (7). Recent investigations have in fact shown that polynuclear carbonyl compounds with more than about 3-4 metal atoms exhibit electronic properties that are practically identical to those of corresponding CO chemisorption systems (8, 9), thus supporting the idea that the bond is relatively strongly localized to a small number of metal atoms forming the chemisorption site. 

As already mentioned, it is the volatile constituents that serve to identify fruit type and variety. Broadly speaking, qualitative analysis will identify the principal substances present in the volatiles fraction as representative of a particular fruit type, but it is the relative proportions of these substances that will reflect the variety. Alcohols, volatile acids, esters, carbonyl compounds, and low-boiling hydrocarbons are the principal groups represented. Analysis by GC-MS (gas chromatography coupled with mass spectroscopy) can be used to provide quantification and identification of the various constituents. 

Our earlier work with Rh6(CO)i6 was the first example of using a transition metal carbonyl compound for catalyzed oxidations. We now find that Rh6(CO)16 is not unique in functioning as a homogeneous catalyst for oxidizing ketones. The dimer Re2(CO)10 is equally effective. The reaction mixture is homogeneous throughout the catalytic reaction. The carbonyl is not decomposed and can be recovered quantitatively at the end of the oxidation. This latter situation even prevails when the oxidations are carried out in the absence of carbon monoxide. Species characterization is done by isolation methods or by IR spectroscopy in the carbonyl region. 

Leigh could prove the formation of siloxetanes 525 from carbonyl compounds and silatrienes 524 obtained through the photolysis of aryldisilanes 523 (equation 178)136,137 140 249. q iey thermally and hydrolytically unstable but an unambiguous assignment was possible through NMR spectroscopy. The yield of siloxetanes... 

Chromium-based reagent systems, for pinacol coupling, 11, 63 Chromium carbenes, in ene-yne metathesis, 11, 272 Chromium carbonyl compounds with bridging hydrides, 5, 206 computational studies and spectroscopy, 5, 203 experimentally determined structures, 5, 204 nitro and nitroso compounds, 5, 205 silatropic migrations, 5, 249 with very weakly bonded ligands, 5, 205 Chromium carbonyl hydrides, preparation and characteristics,... 

Lawesson s reagent (LR) is a very effective thionating agent of carbonyl compounds. However, attempted thionation with LR of iV-alkylhydroxamic acids gave maximum yields of 55-60%. Previous work had established that the thionation products, the thiohydroxamic acids (THA), were accompanied by the corresponding amides (A) formed by reduction and the thioamides (TA), the products of thionation of the amides (A) (Scheme 16). Now the reaction of (V-isopropylhydroxamic acid (HA R = IV) with LR has been followed by 31P NMR spectroscopy and several P-containing intermediates have been identified. This has permitted the delineation of a rational, but complex, pathway to each of the products of the reaction.45... 

---