2,4-Pentanedione structure

Many lanthanide shift reagents are now available commercially which are soluble in common organic solvents. Most of the reagents are lanthanide complexes of -diketones having the basic 2,4-pentanedione structure. Some common reagents are Pr(fod)3, Eu(tfa)3, Yb(hfa)3 and also associated permutations. The shift reagents are tris-yS-diketonates of... 

LiCH[C(0)CHj]2 (lithium 2,4-pentanedionate) [structure consists of endless strings of pseudo Li(acac)2 groups (acac = acetylacetonate), connected by bridging lithium atoms there are two different types of lithium geometry tetrahedral and tetragonal. 

Both of these features are apparent m the structure of the enol of 2 4 pentanedione shown in Figure 18 2... 

Owing to their particular interest two individual reactions will now be discussed separately. The reaction of methoxycarbonylhydrazine and 3-bromo-2,4-pentanedione affords, in addition to the expected pyrazole (608), a pyrazolium salt (609), the structure of which was established by X-ray crystallography (74TL1987). Aryldiazonium salts have been used instead of arylhydrazines in the synthesis of pyrazolines (610) and pyrazoles (611) (82JOC81). These compounds are formed by free radical decomposition of diazonium salts by titanium(n) chloride in the presence of a,/3-ethylenic ketones. 

How many different enolates may arise from deprotonation of 2,4-pentanedione Draw Lewis structures for each, and predict which is likely to be the most stable. Check your conclusions by examining the energies of the different possible enolates (enolate A, B...). Is the most stable enolate that derived from deprotonation of the most electron-poor hydrogen Compare the electrostatic potential maps of the anions with each other and with your Lewis structures. Revise your drawings to be consistent with the maps. Why is one of the enolates preferred over the others ... 

By learning to recognize such three-atom groupings within larger structures, resonance forms can be systematically generated. Look, for instance, at the anion produced when H+ is removed from 2,4-pentanedione by reaction with a base. How many resonance structures does the resultant anion have ... 

The 2,4-pentanedione anion has a lone pair of electrons and a formal negative charge on the central carbon atom, next to a C=0 bond on the left. The 0=C-C grouping is a typical one for which two resonance structures can be drawn. 

Just as there is a C=0 bond to the left of the lone pair, there is a second C=0 bond to the right. Thus, we can draw a total of three resonance structures for the 2,4-pentanedione anion. 

Metal acetylacetonates (M-ac.ac), also known as pentanedionates, are produced by reacting metals and acetyl acetone. They have the following chemical structure ... 

The adducts formed with acetone, cyclopentanone, cyclopentanedione, 2,4-pentane-dione or 3-methyl-2,4-pentanedione (See Structure strOl, p. S-l, R=CH3CO.CH2, etc.) form insoluble potassium salts (M=K), but these are highly explosive and shock-sensitive and should not be isolated, but handled only in solution. 

Bis(2,4-pentanedionato)zinc hydrate forms white crystals which melt at 138 to 140° to a milky liquid. It is rather unstable toward heat, decomposing into mesitylene and an acetate-containing compound of the formula Zn2(CH3C02)(C5H702)3.2 The latter also tends to form on dissolution of the hydrate in cold organic solvents, but this can be prevented by adding 2,4-pentanedione to the solution. The crystal structure of bis-(2,4-pentanedionato)zinc hydrate has been determined recently.3... 

The scope of the condensation reaction has been extended considerably by varying the dicarbonyl compound employed. Diethyl 3-oxoglutarate, acetylacetone (2,4-pentanedione), and other compounds with structures analogous to that of ethyl acetoacetate, form compounds of constitution similar to that of II. 

The tris and bis complexes of acetylacetone (2,4-pentanedione) (167) with chromium(III) have been known for many years (168,169).739 The tris compound is generally prepared by the reaction of an aqueous suspension of anhydrous chromium(III) chloride with acetylacetone, in the presence of urea.740 Recently a novel, efficient synthesis of tris(acetylacetonato)chromium-(III) from Cr03 in acetylacetone has been reported.741 The crystal structure of the tris complex has been determined.744 A large anisotropic motion was observed for one of the chelate rings, attributed to thermal motion, rather than a slight disorder in the molecular packing. 

Exercise 17-4 a. The proton nmr spectrum of 2,4-pentanedione is shown in Figure 17-1. Interpret this spectrum by assigning each resonance to a structurally different proton, and explain why the broad resonance at 15 ppm is at unusually low field strengths. 

Exercise 23-21 2,4-Pentanedione reacts with methanamine to give a product of composition CgHnNO that is an equilibrium mixture of three isomers. The nmr spectrum of the mixture indicates that all three isomers have strong hydrogen bonding. Draw the structures of the three isomers and indicate the nature of the hydrogen bonding. 

Ketone Peroxides. These materials are mixtures of compounds with hydroperoxy groups and are composed primarily of the two structures shown in Table 2. Ketone peroxides are marketed as solutions in inert solvents such as dimethyl phthalate. They are primarily employed in room-temperature-initiated curing of unsaturated polyester resin compositions (usually containing styrene monomer) using transition-metal promoters such as cobalt naphthenate. Ketone peroxides contain the hydroperoxy (—OOH) group and thus are susceptible to the same hazards as hydroperoxides. By far the most popular commercial ketone peroxide is methyl ethyl ketone peroxide [1338-23-4]. Smaller quantities of ketone peroxides such as methyl isobutyl ketone peroxide [28056-59-9], cyclohexanone peroxide [12262-58-7], and 2,4-pentanedione peroxide [37187-22-7] are used commercially (47). 

However, the acidity of the a proton gets increased if it is flanked by two carbonyl groups rather than one, for example, 1, 3-diketones ((i-di ketones) or 1,3-diesters ([i-keto esters). This is due to the fact that the negative charge of the enolate ion can be stabilised by both carbonyl groups which results in three resonance structures (Following fig.). For example, the pKa of 2, 4-pentanedione is 9. 

Figure 4.43. Thermogravimetric analysis of organomagnesium CVD precursors, indicating the dependence of molecular structure on its decomposition temperature. The ligand abbreviations are dpm = 2,2,6,6-tetramethyl-3,5-heptanedionate, TMEDA = Ai, Ai, A, W -tetramethylethylenediamine, hfa = l,l,l,5,5,5-hexafluoro-2,4-pentanedione, HTEEDA = H(W, N, N, A Atetraethylethylene diamine). Reproduced with permission from Chem. Mater. 2005,17(23), 5697. Copyright 2005 American Chemical Society.

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