Enolates drawing

When the following compound is treated with sodium ethoxide, nearly all of it is converted into an enolate. Draw the resonance structures of the enolate that is formed, and explain why enolate formation is nearly complete despite the use of ethoxide rather than LDA... 

Methylcyclohexanone is treated with one molar equivalent of LDA to form an enolate. Draw the structure of the product of the reaction of the enolate with diethyl oxalate. 

Compare electrostatic potential maps of enolates derived from 2-butanone, 4,4-dimethyl-2-pentanone, 4,4,4-trifluoro-2-butanone and l-phenyl-2-propanone with those of acetone. Which substituents cause significant changes in the electronic structure of these enolates and what are the nature of these changes Justify your answers by making drawings of any important resonance contributors. 

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 ... 

Which of the two enolates enolate A or enolate B) is lower in energy Rationalize your observation by comparing their structures, charge distributions and electrostatic potential maps. Draw all of the resonance contributors needed to describe each enolate. Which enolate is generated by reaction with NaH ... 

The hydroxythiophenes which exist predominantly as the thiolen-2-ones also show reactions characteristic of the enol form. They can be methylated at the oxygen with dimethyl sulfate of diazomethane and they can also be acylated. - - They also react as thio-lene-2-ones showing a reactive methylene group which can be condensed with benzaldehyde. The danger of using chemical reactivity data for drawing conclusion as to the physical state of these tautomerizable systems has been pointed out. ... 

Problem 22.1 Draw structures for the enol tautomers of the following compounds ... 

There are two ways of representing this, according to which resonance form of the enolate anion is used. Although the preferred resonance form (charge located on the oxygen atom) should be used as the nucleophile, because carbon is acting as the nucleophile and a new C-Br bond is formed, the less-favoured resonance form is frequently employed in mechanistic pathways. This makes mechanism drawing rather easier, but is technically incorrect. 

The irreversible elimination drives the reversible aldol reaction and gives a favourable conjugated ketone in a favourable six-membered ring. On paper, one could also draw an acceptable mechanism in which the order of events was reversed. This is not so neat, and would require generating an enolate anion y to the a,P-unsaturated ketone formed by the first aldol-dehydration sequence. 

Intramolecular alkylation of enolates has been used to advantage in synthesis of bi-and tricyclic compounds. Indicate how such a procedure could be used to synthesize each of the following molecules by drawing the structure of a suitable precursor. 

The 1carbanions1 we formed using the carbonyl group are like enols and are called enolate anions. Draw the enolate anion from this ketone 0... 

Draw the arrows for the re-protonation of this enolate to give the original compound. 

In the next section we shall he looking at more reactions of ends which make new carbon-carton bonds. We ll finish off this section with review questions. Draw the most stable enol from ... 

The adduct then decomposes with the loss of the enolate anion of the ester as a leaving group. Draw this. 

Draw out the mechanism for the conversion of the keto to the enol form in base. 

H2 0 H ioxi2 Now draw the enol form of this ketone CH3CO.CH2.COCH3. 

Draw the enolate anion from cyanoacetic ester EtOOC.CH2.CN, and show how it is stable. 

This intermediate is of course another, less stable, enolate anion, and in the ethanolic solution it will protonate to give the final product. Draw this. 

The ketodiester 88 was made from furfural 78 by a Wittig reaction and treatment of the product 87 with acidic methanol.14 The central carbon atom in 88 can be seen as an enol ether in 87. You might like to try to draw a mechanism for this extraordinary reaction which is described in detail in the workbook. 

The disconnection looks tricky but it is all right if you simply reverse the rearrangement, by drawing the mechanism for the imaginary reverse reaction. There may well be two possible starting materials. Thus cyclopentene 40, needed for a photochemical experiment, could be disconnected as 40a or 40b. There is no obvious way to continue from 41 but 42 has an enone that could be made from aldehyde 43 and some reagent for the enolate of acetone 44. 

Making the Diels-Alder disconnection by drawing the mechanism of the reverse reaction 31a gives a new enol ether 32 and a quinone 33. The enol ether 32 is a derivative of the simple enone 34 and can be made by trapping the kinetic enolate with a suitable silyl group. 

The FO treatment of enolate regioselectivity presented in Section 5.2.2 is based on the MOs of enol. Let us first check that the conclusions remain unchanged if the MOs of the naked enolate or of the enolate accompanied by its counterion are used instead. Figure 5.4 shows the C and O net charges in CH2=CHO , CH2=CHOLi and CH2=CHONa, according to PM3, STO-3G and 3-21G calculations.40 Below each drawing are shown the energies (in eV) of the two occupied n orbitals and the ratios of the C and O coefficients in each MO. 

Assuming ionic Li 0 or Li NR interactions, it may be appropriate to draw a parallel between the structures of enolates and ionic crystals of the Li 0 or Li NR types. In the latter structures, every lithium atom is coordinated by six neighboring anions. 

In drawing mechanisms, you can show either resonance form of an enolate attacking the electrophile. 

Propose mechanisms for the reactions shown in Problems 22-62 parts (a) and (b) and 22-63 parts (a) and (b). Pentane-2,4-dione (acetylacetone) exists as a tautomeric mixture of 8% keto and 92% enol forms. Draw the stable enol tautomer, and explain its unusual stability. 

This is a better mechanism for enolization than those we have been drawing because it shows that something (here a water molecule) must actually be removing the proton from carbon. Though this reaction will occur faster than the uncatalysed enolization, the equilibrium is not changed and we still cannot detect the enol spectroscopically. 

Notice that in drawing this mechanism It is not necessary to locate the negative charge on the carbon atom. You should always draw enolate mechanisms using the better oxyanion structure. 

Draw all the possible enol forms of these carbonyl compounds 2. The proportions of enol in a neat sample of the two ketones and comment on the stability of the various enols. below are shown. Why are they so different ... 

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