Caibonyl group

Activated Zn, MeOH, reflux, 12 h, 89-96% yield. This ketal is stable to several reagents that react with caibonyl groups (e.g., m-ClC6H4C03H, NH3, NaBH4, and MeLi). It is cleaved under neutral conditions. 

Fig. 8.3. Three-dimensional potential energy diagram for addition of a proton and nucleophile to a caibonyl group, (a) Proton transfer complete before nucleophilic addition begins (b) nucleophilic addition complete before proton transfer begins (c) concerted proton transfer and nucleophilic addition.

The caibonyl group in aldehydes, ketones, acids, esters, and amides is deactivating and wcto-directing. There are distinct limitations on the types of substitution reactions that are satisfiictory for these deactivating substituents. In general, only those electrophiles in category A in Scheme 10.1 react readily. 

Protons on caibons adjacent to a caibonyl group are deshielded slightly more than allylic hydrogens. 

We will have more to say about chemical shifts in later chapters when vaii-ous families of compounds, especially those that contain caibonyl groups, aie discussed in more detail. 

Steps 1-3 Acid-catalyzed nucleophilic addition of 1 mole of ethanol to the caibonyl group. The details of these steps are analogous to the three steps of acid-catalyzed hydration in Figure 17.7. The product of these three steps is a hemiacetal. 

In the presence of bases such as hydroxide, methoxide, and ethoxide, these p-diketones aie converted completely to their enolate ions. Notice that it is the methylene group flanked by the two caibonyl groups that is deprotonated. Both caibonyl groups paitici-pate in stabilizing the enolate by delocalizing its negative chaige. 

The caibonyl group withdraws tt electron density from the double bond, and both the caibonyl caibon and the p caibon aie positively polaiized. Their greater degree of charge separation makes the dipole moments of a,p-unsaturated carbonyl compounds significantly larger than those of comparable aldehydes and ketones. 

Section 19.17 1,1-Dicarboxylic acids (malonic acids) and p-keto acids undergo thennal decar boxylation by a mechanism in which a p-caibonyl group assists the departure of carbon dioxide. 

Step 2 Nucleophilic addition of the ester enolate to the caibonyl group of the neutral ester. The product is the anionic fonn of the tetrahedral intennediate. 

Note. The term potential aldehydic carbonyl group refers to the hemiacetal group arising from ring closure. Likewise, the term potential ketonic caibonyl group refers to the hemiketal structure (see 2-Carb-5). 

Conjugation with olefinic or acetylenic groups lowers the frequency and raises the intensity. Conjugation with caibonyl groups usually has little effect on the position of absorption. 

Molecules containing multiple carbonyl groups may be oxidized with group selectivity. For example, cyclobutanones are hi y reactive and ring expand even widi basic HOOH. Relative reactivities of steroidal ketones depend upon the position of die caibonyl group (equations 11 to i3),2i.s9. o Cyclohexa-... 

The anodic a-acetoxylation or a-methoxylation of ketones has been shown to be a powerful tool for the 1,2-transposition of the caibonyl group. The overall process is described by equation (24). ... 

Treatment of an aldehyde or ketone with a 1 amine affords an imine (also called a Schilf base). Nucleophilic attack of the 1° amine on the caibonyl group forms an unstable carbinolamine, which loses water to form an imine. The overall reaction results in replacement of C=O by C=NR. 

MEERWEIN - PONNOORF VERLEY Reduction Reduction ol caibonyl groups to aicohols by means of AI(iPrO)3 end aopropanol... 

Among the other hydride donors [S91], organometallic reagents bearing a C-H bond in the 0-position can be used for reduction of carbonyl compounds. In such reactions, direct addition of the organometallic substituents to the caibonyl group must be avoided. Meerwein-Verley-Pondorf reductions [624b] have also been studied, as have reductions based on models of NADH [625],... 

Reductive rouf ing of caibonyl groups Tiianium(IV) chluride- Zinc, 310 From ihrcc>mcmbercd hctcrocycles Ary tvelenocarboxamidcs, 22 Tiianium(lV) chloride-Lithium alumi-num hydride, 310... 

Tlte structure of Knecht compound has been examined by 7. l. rbanski a Zys/.ezynski [54. On the basis of infra red spectra they came to a conclusii that the cellulose moiety of the Knecht Compound is partly oxidized and shov the presence of a caibonyl group similar to that erf oxycellulose t Vol. II, p. 321... 

Products of photooxidation free radicals, unsaturations, caibonyl groups, Itydroperoxides, chain scissions... 

Figure13.32. strwrtuieoftherigidsteroiddoim-accefitorpurCO.tfae steroid cM aining the ck>iK alone (II), and the Steroid cmteimng the seeeptor aloM (III). Indole is the donor and the caibonyl group is the acceptoc Revised frocmRjeC. 18.

When the reaction is initiated bv primary amines, the first step is a nucleophilic attack by the amine on the C5 of the anhydride. The carbon dioxide that is released comes from the C2 carbonyl group. The propagation proceeds by addition of terminal amine groups to the C5 caibonyl groups of the monomers... 

Plasticizers may protect PVC from UV degradation. Figure 11.65 shows that addition of diisoundecyl phthalate protects C-Cl bond from dissociatiom Also, caibonyl group formation is reduced in the presence of plasticizers. 

Activated caibonyl groups serve as excellent substrates in Lewis acid catalyzed cyclization reactions, with faster reaction rates and higher yields being obtained in related cyclization processes involving acetals and ketals. Thus, treatment of the dimethyl acetals (20a-c) with TiCU at -78 C afforded the Inaryl... 

Tire formal addition of an oxygen atom across the caibonyl group gives rise to dioxiranes (equation 33). In practice, this reaction is effected widi Oxone, and dhnediyldioxirane (30) and other dioxiranes have been generated in solutions of dreir parent ketones. Dioxiiane (30) has been implicated in oxida-... 

PMMA Residual initiator and monomer (Crosslinks, foimaldehyde, methanol, methyl formate, hydrogen, CO, CO2 Crosslinks, hydtt eroxides, hydro and caibonyl groups, aldehydes... 

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