Carbonyls compounds

The carbonyl group has an influence on the chemistry of substituents. The electron donation from the lone pairs on oxygen and nitrogen in esters and amides not only diminishes the reactivity of the carbonyl group towards nucleophiles, but also reduces the basicity of the oxygen and nitrogen atoms. 

The electron-withdrawing effect of the carbonyl group makes hydrogen atoms attached to neighbouring atoms acidic (Box 3.2). Once the anion is formed, it may achieve stability by delocalization of the negative charge over the carbonyl group. 

The addition of a nucleophile to the carbonyl group involves the conversion of a planar sp centre to a tetrahedral sp centre with an increase in the steric bulk of the intermediate. The preferred direction of approach of the nucleophile to the carbonyl carbon is along an axis through the carbon and oxygen atoms and at an angle of 108° to the plane of the carbonyl group (see 3.7). 

The face of the carbonyl group which is attacked by a nucleophile may be influenced by the size of the adjacent substituents. Several models 

Carbonyl-like reactivity is found with a number of other functional groups. Replacement of the oxygen of the carbonyl (C=0) group with nitrogen leads to imines(C=N-R) and to nitriles (CsN). These possess both an electron-deficient carbon and adjacent substituents which are activated by the imine (see 3.9) or nitrile (see 3.10). 

Carbonyl compounds in oxidized lipids are the secondary oxidation products resulting from the decomposition of the hydroperoxides. They can be quantified by the reaction with 2,4-dinitrophenylhydrazine and the resulting colored hydrazones are measured spectrophotometrically at 430-460 nm. The carbonyl value is directly related to sensory evaluation, because many of the carbonyl molecules are those responsible for off-flavor in oxidized oil. The anisidine value is a measure of carbonyl compounds that have medium molecular weight and are less volatile (Frankel 1998). It can be used to discover something about the prior oxidation or processing history of an oil. 

Carbonyl compounds are usually characterized by the preparation of some of their derivatives. The more important derivatives are semicarbazones, thiosemicarbazones, oximes and 2 4 dinitrophenylhydrazones. The absorption spectra of these derivatives are appreciably different from those of the 

It may be seen from Table 4.7 that the derivatives of a -unsaturated carbonyl compounds exhibit absorption bands at considerably longer wavelengths than the derivatives of simple saturated carbonyl derivatives. 

Data on the ultra-violet absorption spectra of these derivatives have been compiled by Gillam and Stern10. In addition to giving confirmatory evidence for the presence of an isolated or conjugated carbonyl group in a molecule, the characteristic intense bands of these derivatives render it possible to 

Glyoxal, (HCO)2, and biacetyl, (CH3CO)2, exhibit only weajc n tt bands around 450 (e 20). The bands show fine structure in non-polar solvents. Polar solvents shift the bands to lower wavelengths and diminish the structural character. 

Leonard and co-workers12 have studied the spectra of some diaryl ketones and of a series of cyclic diketones 

Since fluoro-carbonyl compounds are such useful and versatile synthetic intermediates, much effort has been devoted to their preparation [124], but only in a few instances has elemental fluorine been used directly. One of the earliest successful direct fluorinations of a simple carbonyl compound was the fluorina-tion of pyruvic acid derivatives which have a high enol content (R = Aryl, Acyl) (Fig. 47) [125] in the solvent being used (mixtures of CF2C1CFC12 and acetonitrile). However, in derivatives where the enol content was low (R = Alkyl), complicated mixtures of products were obtained. 

Recently, it has been shown that /1-diketones [126],/ -ketoesters (Fig. 48) [126] and N, N-dialkyl-/ -ketoamides [127] can be fluorinated directly, in high yield, at convenient temperatures (0 10 °C), in polar solvents such as formic acid or acetonitrile. As in the case of the pyruvates, the overall rate of reaction was a 

Diketones react more rapidly with fluorine than the corresponding keto-esters, and dialkyl malonates do not react at all under these conditions. However, if dialkyl malonates are first converted into their sodium salts, reaction with fluorine gives the corresponding fluoro-compound (Fig. 50) [128]. 

Attempts to use fluorine in the preparation of simple a-fluoro-carbonyl compounds were not successful initially. Even when derivatives of carbonyl compounds such as enol acetates were treated with fluorine, a complicated mixture of products was obtained from which none of the desired a-fluoro 

Under similar conditions, the enol acetate and the trimethylsilyl ether of estrone were fluorinated to give the corresponding a-fluoro carbonyl compound (Fig. 54) [135]. 

Acetaldehyde is the major important carbonyl compound of alcoholic fermentation and is formed as an intermediate compound by degradation of pyruvate  

10 Flavour of Spirit Drinks Raw Materials, Fermentation, Distillation, and Ageing 

Compound Flavour quality Threshold (mgL water) Threshold (mgT ethanol solution) Typical concentration [mgL (40% v/v)]  

Ethyl acetate Solvent-like, nail polish 17.6 7.5 4-800 

You have now learned that in the organic compounds known as alcohols and ethers, oxygen is bonded to two different atoms. In other kinds of organic compounds, an oxygen atom is double-bonded to a carbon atom. 

Aldehydes An aldehyde is an organic compound in which a carbonyl group located at the end of a carbon chain is bonded to a carbon atom on one side and a hydrogen atom on the other. Aldehydes have the general formula CHO, where represents an alkyl group or a hydrogen atom. 

Aldehydes are formally named by changing the final -e of the name of the alkane with the same number of carbon atoms to the suffix -al. Thus, the formal name of the compound represented above is methanal, based on the one-carbon alkane methane. Methanal is commonly called formaldehyde. A water solution of formaldehyde was used in the past to preserve biological specimens. However, formaldehyde s use has been restricted in recent years because evidence shows it may cause cancer. Industrially, large quantities of formaldehyde are reacted with urea to manufacture a type of grease-resist-ant, hard plastic used to make buttons, appliance and automotive parts, and electrical outlets, as well as the glue that holds the layers of plywood together. 

Note the relationship between the structures and names of ethane and ethanal in the following diagram. 

The major pathway leading to the formation of carbonyls is the Strecker degradation. This reaction occurs between dicarbonyls and free amino acids. The dicarbonyls involved have vicinal carbonyls (carbonyl groups separated by one double bond) or conjugated double bonds [41], While these carbonyls typically are intermediates in the Maillard reaction, they may also be normal constituents of the food (e.g., ascorbic acid), be end products of enzymatic browning (e.g., quinones), or be products of lipid oxidation[42]. 

The end products of the Strecker degradation are COj, an amine, and the corresponding aldehyde of each deaminated and decarboxylated amino acid. At one time these aldehydes were considered to be quite important to the flavor of heated food products. This was primarily because they are the most abundant volatiles formed via the Maillard reaction (and thus assumed to be important). It is now realized that the heterocyclic volatiles are more important. The Strecker aldehydes are often monitored in foods since they are present in quantity and can serve as indicators of the Maillard reaction [43]. 

Strecker aldehydes may also be formed via free radical mechanisms [44]. The oxidation of amino acids by hydrogen peroxide or lipid peroxides yields CO2, ammonia, and the corresponding Strecker aldehydes. While this is a viable pathway for the production of Strecker aldehydes, the above-mentioned pathway typically predominates. 

The reaction of carbonyl difluoride with carbonyl compounds follows the general pattern of addition of the F and C(0)F units across the unsaturated C=0 entity. However, the resulting fluoroformate can be frequently readily decarboxylated to the corresponding 

I Identify the structures of carbonyl compounds, including aldehydes, ketones, carboxylic acids, esters, and amides. 

I Discuss the properties of compounds containing the carbonyl group. 

Carbonyl compounds contain a double-bonded oxygen in the functional group. 

Real-World Reading Link Have you ever eaten a piece of fruit-flavored candy that tasted like real fruit Many natural fruits, such as strawberries, contain dozens of organic molecules that combine to give the distinctive aroma and flavor of fruits. The carbonyl group is found in many common types of artificial flavorings. 

FIGURE 2.35 Normal base values for the C=0 stretching vibrations for carbonyl groups. 

A carboxylic acid exists in monomeric form in very dilute solution, and it absorbs at about 1760 cm because of the electron-withdrawing effect just discussed. However, acids in concentrated solution, in the form of neat liquid, or in the solid state (KBr pellet and Nujol) tend to dimerize via hydrogen bonding. This dimerization weakens the C=0 bond and lowers the stretching force constant K, resulting in a lowering of the carbonyl frequency of saturated acids to about 1710 cm .  

Ketones absorb at a lower frequency than aldehydes because of their additional alkyl group, which is electron donating (compared to H) and supphes electrons to the C=0 bond. This electron-releasing effect weakens the C=0 bond in the ketone and lowers the force constant and the absorption frequency. 

Conjugation Effects. The introduction of a C=C bond adjacent to a carbonyl group results in delocalization of the n electrons in the C=0 and C=C bonds. This conjugation increases the singlebond character of the C=0 and C=C bonds in the resonance hybrid and hence lowers their force constants, resulting in a lowering of the frequencies of carbonyl and double-bond absorption. Conjugation with triple bonds also shows this effect. 

The following examples show the effects of conjugation on the C=0 frequency. 

The most important reactions which provide volatile carbonyl compounds were presented in sections 3.7.2.1.9 (lipid peroxidation), 4.2.4.3.3 (caramelization) and 4.2.4.4.T (amino acid decomposition by the Strecker degradation mechanism). 

Some Strecker aldehydes found in many foods are listed in Table 5.16 together with the corresponding aroma quality data. Data for carbonyls derived from fatty acid degradation are found in Table 3.32. Carbonyls are also obtained by degradation of carotenoids (cf. 3.8.4.4). 

Contrary to some reports, electrophilic addition reactions may occur in other multiple-bond systems. In many of the reactions of aldehydes and ketones the first stage involves the addition of some entity across the carbon-oxygen bond, e.g., the formation of oximes, semicarbazones, hydrazones, hydrates (1,1-diols) and their ethers, and the aldol condensation. Most of these reactions entail a subsequent loss (elimination) of a small molecule e.g. water, ammonia, ethanol) and, while one must be careful to determine whether the rate-determining stage involves attack on the carbonyl compound or elimination from the adduct , there are some systems in which it is evident that electrophilic attack is involved in the slow stage of the reaction sequence. Examples of such reactions are the acid-catalysed formation of oximes of aliphatic - and aromatic carbonyl compounds, of furfural semi-carbazone , and of 1,1-diols from aldehydes or ketones . 

Similarly, the acid-catalysed hydrolysis ofoximes or of nitriles or amides doubtless involve electrophilic addition to carbon-nitrogen multiple bonds. 

Such reactions will not be dealt with (see Vols. 10 and 12). The addition of water to carbonyl compounds, however, deserves mention here. The reaction is reversible, viz. 

As well as such additions to aldehydes and ketones, there are a number of addition reactions involving other multiple bonds some of these show definite electrophilic character-.  

A drastic approximation had to be made for the hydrogens their total charge was deduced from charge normalization and was entirely treated as atomic charges of hydrogens attached to carbon, i.e. as if was always null in the OH part, which is wrong, of course. 

This shortcut does not help improve the quahty of our presentation. Indeed, one single miUielectron erroneously attributed to a hydrogen atom attached to carbon (with fljjc = 0.632), rather than to a hydroxyl H atom (with a Q = 1.000 kcal 

The case of water is treated differently. It is correctly calculated as 

The CO double bond of acetone introduces a new reference energy  

Direct estimates using the appropriate SCE potentials at the nuclei suggest 181 kcal/mol [141]. The CC and CH parameters are treated the usual way. A general formula is developed as follows. The hydrogen charge variations are expressed relative to q = —W.l me. Charge normalization, (X) c + 

Simple electron transfer followed by rapid protonation would give the ketyl radical which dimerises very rapidly. 

Cr(II) reduction of benzaldehyde in aqueous acidic ethanol also yields largely hydrobenzoin although other products were characterised, e.g. hydrobenzoin monoethyl ether, and a 1 1 stoichiometry is preserved. The rate law in ethanol acidified both with HCIO4 and HCl is complex for example, in HCl-ethanor°°, 

The process of ligand transfer to give CrCP is well-established in the case of Cr(II) reduction of alkyl halides. 

Conversion of diethyl ether into triethyloxonium tetrafluoroborate deshields the a while shielding the y carbon atom. The reason is not only the positive charge at oxygen but also an additional /I and y effect introduced by the third ethoxy group. 

An alkoxy group at the double or triple bond polarizes the n system in a similar manner but more strongly than that described for halogens (Section 4.4.3). The a effect is predominantly inductive, while the jK effect results from electron donation induced by the nonbonding pairs at the alkoxy oxygen  

strong shieldings are observed for fi carbons of enol ethers and alkynyl ethers, as shown for 1,1 -dimethoxyethene (54.7 ppm) and ethoxyethyne (23.4 ppm) in Table 4.26. In 1-alkoxy-l,3-butadienes, transmission of the electron releasing effect along the conjugated double bonds affects alternate carbons similarly, shielding the carbons in / and 5 position as illustrated for l-ethoxy-2-methyl-l,3-butadiene. 

Cis-trans isomeric enol ethers can be distinguished by using the 5trans 5cis relation for the at but not for the alkoxy carbons, which follow a reverse pattern (Table 4.26). 

Carbonyl carbon-13 shifts of aldehydes, ketones and carboxylic acids, including all derivatives, occur between 150 and 220 ppm [281]. Within this range, carboxy carbons are shielded (150-180 ppm) relative to carbonyl carbons in aldehydes and ketones (190-220 ppm). This is attributed to an electron releasing effect of the additional hetero 

The transition in the 230-253-nm region has been studied in detail. From vibrational analysis it follows that the CO bond is lengthened from 120.3 pm in the ground state to 132 pm in the Aj(n, n ) state, while the CHj group is bent out of the molecular plane by 25-30°. (Cf. Table 1.4, Section 1.4.1.) The barrier to inversion is small and gives rise to a prominent inversion doubling with v = 356 cm (Moule and Walsh, 1975). 

The extinction coefficient, e = 20, is very small. The low intensity is typical for most n- jr transitions of carbonyl compounds and can be explained on the basis of the local symmetry. In the case of formaldehyde, which has Cjv symmetry, an electronic transition from the n orbital (b2) into the jt MO (b ) is dipole forbidden. This is no longer true for carbonyl compounds of lower symmetry such as acetaldehyde (CJ. Here the n orbital is still essentially of p character, so that the overlap density is approximately p Py and still has practically no dipole moment. 

An intensity enhancement has been observed for /3,y unsaturated carbonyl compounds such as 32, which is due to r-.7r interactions in the non-planar system of reduced symmetry (Labhart and Wagniere, 1959). In the series of polyene aldehydes, of the transition increases with in- 

Azo compounds also have two lone pairs of electrons that can interact through space or through bond. Azomethane 33 (R = CH,) has been studied in detail. In the cis form 33a the n, orbital is below the n orbital and the transition at 353 nm is allowed, e = 240. In contrast, the energy order of the n orbitals is reversed in the trans compound 33b, as is to be expected from the negative overlap of the sp -hybridized n orbitals. The n,—transition at 343 nm is therefore symmetry forbidden, as is seen from the value e = 25 (Hasel-bach and Heilbronner, 1970). For azobenzene 33 (R = Ph) the corresponding 

Whereas for the aza analogues of benzene and naphthalene the n—transitions can be observed as separate bands or as shoulders on the ji— n transitions, they are usually hidden by transitions in higher aromatics. 

Note The directions for the experiments are for semimicro work. For macro work, use five times the quantities given instead of an e ht-inch tube, use a 250-500 ml flask, a Liebig condenser instead of a micro condenser, a distilling flask instead of a distilling tube. Use the same directions and allow about 50 per cent more time. 

The general equation above merely indicates the beginning. The ultimate direction depends on the environment, temperature, catalyst nature of the aldehyde, and other factors. 

Though the use of special names is considered unfortunate from the point of view expressed above, the usage is widespread in chemical literature, and the student will do well to get acquainted with the specific application of each. The most important are  

The reaction represented by the equation is the first step, which is reversible. Loss of water by the hydroxyaldehyde results in an unsaturated compound. 

A similar reaction may occur between an aldehyde and a ketone to form an unsaturated ketone. 

56 See Terpenoids and Steroids ed. J. R. Hanson (Specialist Periodical Reports), The Chemical Society, London, 1978, Vol. 8, p. 240. 

Additionally, ADMET polymers containing y-butyrolactone have also been synthesized v rith [Ru]l and [Ru]2 [86]. 

ADMET has also been used to synthesize liquid-crystalline polyesters [87]. The alkenyl chains used as ADMET monomers can be easily attached to a rigid mesogen that yields, upon polymerization, the alternating flexible-rigid-flexible structural motif often employed for liquid-crystalline polymers (LCPs). 

A series of unsaturated poly(phosphoesters) have also been synthesized v rith ADMET [88]. These materials proved to be synthetically quite accessible, and potentially degradable and biocompatible. Moreover, their thermal properties were controllable, with tunable melting points or glass transition temperatures. 

Diketopiperazine-based dienes have also been polymerized by ADMET to form polyesters [89]. Dynamic light scattering and differential scanning calorimetric measurements indicated that these materials formed aggregates in Ar,AT-dimethylformamide, which is presumably due to the hydrogen bonding between diketopiperazine moieties. 

Copyright 2013 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. 

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SchifT s bases A -Arylimides, Ar-N = CR2, prepared by reaction of aromatic amines with aliphatic or aromatic aldehydes and ketones. They are crystalline, weakly basic compounds which give hydrochlorides in non-aqueous solvents. With dilute aqueous acids the parent amine and carbonyl compounds are regenerated. Reduction with sodium and alcohol gives... 

Wong S K, Hutchinson D A and Wan J K S 1973 Chemically induced dynamic electron polarization. II. A general theory for radicals produced by photochemical reactions of excited triplet carbonyl compounded. Chem. Phys. 58 985-9... 

Additional gas-phase reactivity data, such as gas-phase acidities of alcohols [41], proton affinities of alcohols and ethers [41], and proton affinities of carbonyl compounds [42] could equally well be described by similar equations. 

Aldehydes and ketones may be converted into the corresponding primary amines by reduction of their oximes or hydrazones (p. 93). A method of more limited application, known as the Leuckart Reaction, consists of heating the carbonyl compound with ammonium formate, whereby the formyLamino derivative is formed, and can be readily hydrolysed by acids to the amine. Thus acetophenone gives the i-phenylethylformamide, which without isolation can be hydrolysed to i-phenylethylamine. 

The conversion of the compounds under investigation into coloured derivatives (e.g., the separation of carbonyl compounds by conversion into their 2 4-dinitrophenylhydrazones, etc. of hydrocarbons through their picrates of alcohols through their 3 5-dinitrobenzoates of glucose, fructose and other simple sugars through their p-phenylazobenzoyl esters). 

The carbonyl compound may be mixed with an aqueous solution of sodium or potassium cyanide and mineral acid is added, or the bisulphite compound may be treated with an equivalent quantity of sodium cyanide, for example ... 

Suspend 0 25 g. of 2 4-dinitrophenylhydrazine in 5 ml. of methanol and add 0-4 0-5 ml. of concentrated sulphuric acid cautiously. FUter the warm solution and add a solution of 0 1-0-2 g. of the carbonyl compound in a small volume of methanol or of ether. If no sohd separate within 10 minutes, dUute the solution carefuUy with 2N sulphuric acid. CoUect the solid by suction filtration and wash it with a little methanol. RecrystaUise the derivative from alcohol, dUute alcohol, alcohol with ethyl acetate or chloroform or acetone, acetic acid, dioxan, nitromethane, nitrobenzene or xylene. 

For the preparation of 2 4-dinitrophenylhydrazones, dissolve the carbonyl compound (say, 0-5 g.) in 5 ml. of ethanol and add the cal culated volume of the reagent. If a precipitate does not form immediately, dilute with a little water. Collect the derivative and recrystalhse it as above. 

When semicarbazide Ls heated in the absence of a carbonyl compound for long periods, condensation to blurea, NHjCONHNHCONHj, m.p. 247-250 (decomp.), may result occasionally this substance may be produced in the normal preparation of a semicarbazone that forms slowly. Biurea is sparingly soluble in alcohol and soluble in hot water, whereas semicarbazones with melting points in the same range are insoluble in water this enables it to be readily distinguished from a semicarbazone. 

The disadvantages associated with the Clemmensen reduction of carbonyl compounds (see 3 above), viz., (a) the production of small amounts of carbinols and unsaturated compounds as by-products, (h) the poor results obtained with many compounds of high molecular weight, (c) the non-appUcability to furan and pyrrole compounds (owing to their sensitivity to acids), and (d) the sensitivity to steric hindrance, are absent in the modified Wolff-Kishner reduction. 

Phthalic anhydride may be used as the carbonyl compound in the Perkin reaction see the preparation of phthalylacetic acid under Ninhytlrin (Section VIII,14),... 

This preparation illustrates the Reformatsky reaction, which consists in the interaction of a carbonyl compound, an a-halogen ester (e.g., ethyl bromo-acetate) and zinc In the presence of ether or benzene, followed by hydrolysis. 

The above reversible equation indicates that one mol of aluminium iso-propoxlde will reduce directly three mols of the carbonyl compound. It is generally desirable to use excess of the reductant except for aromatic aldehydes for the latter side reactions (e.g., 2RCHO-----> RCOOCH R Tischenko re-... 

The following mechanism of the reaction has been suggested it includes the coordination of the carbonyl compound with the aluminium atom in aluminium sopropoxide and the transfer of a hydride Ion ... 

The reaction between sodium acetylide in liquid ammonia solution and carbonyl compounds gives a-acetylenyl carbinols (compare Section 111,148), for example ... 

Other carbonyl compounds are within the scope of the reaction ketones give amides, and aldehydes yield nitriles and formyl derivatives of amines ... 

The conversion of a carbonyl compound by ammonium polysulphide solution into an amide with the same number of carbon atoms is known as the Willgerodt reaction. The procedure has been improved by the addition of about 40 per cent, of dioxan or of pyridine to increase the mutual solubility of the ketone and aqueous ammonium polysulphide the requisite temperature is lowered to about and the yield is generally better. 

The reactions of organolithium compounds with carbonyl compounds, including carbon dioxide, may be interpreted as follows ... 

Both aldehydes and ketones contain the carbonyl group, hence a general test for carbonyl compounds will Immediately characterise both classes of compounds. The preferred reagent is 2 4-dinilrophenylhydrazine, which gives sparingly soluble phenylhydrazones with carbonyl compounds ... 

Supplement (combined with Volumes XVIII and XIX) XVII, 2nd 1934 2359-3031 Hydroxy compounds Furfuryl alcohol, 112. Carbonyl compounds Butyrolactone, 234. Furfural, 272. 2-Aoetyl-thio-phene, 287. Xanfhone, 366. Succinic anhydride, 404. Phthalio anhydride, 469. 

Supplement 1952 2666-3031 Carbonyl compounds Ethylene carbonate, 100. Piperonal, 116. Thioindigo, 177. Fluorescein, 222. Carboxylic acids Piperonylic acid, 269. Amines, 328. Three Cyclic Oxygens, 381. Four Cyclic Oxygens, 433. Fiite Cyclic Oxygens, 459.. . . ... 

Supplement 1953 3103-3241 Carbonyl compounds a-Pyrrolidone, 236. Tropinone, 259. Succinimide, 369. Isatin, 432. Phthalimide, 458. 

XXIV XXIV, 1st 1936 3555-3633 Two Cyclic Nitrogens (continued). j Carbonyl compounds Antipyrin, 27. 

Determination of the dissociation constants of acids and bases from the change of absorption spectra with pH. The spectrochemical method is particularly valuable for very weak bases, such as aromatic hydrocarbons and carbonyl compounds which require high concentrations of strong mineral acid in order to be converted into the conjugate acid to a measurable extent. 

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