Intramolecular hydrogen-bonded carbonyl

Intramolecular hydrogen bond between the —OH group and the carbonyl oxygen... 

Both enols have their carbon-carbon double bonds conjugated to a carbonyl group and can form an intramolecular hydrogen bond They are of comparable stability... 

Conjugation is more important 1 3 Cyclohexanedione exists mainly in its enol form in spite of the fact that intramolecular hydrogen bonding is impossible due to the distance between the carbonyl group and the enohc —OH group... 

Acyl-, 4-alkoxycarbonyl- and 4-phenylazo-pyrazolin-5-ones present the possibility of a fourth tautomer with an exocyclic double bond and a chelated structure. The molecular structure of (138) has been determined by X-ray crystallography (Table 5). It was shown that the hydroxy group participates in an intramolecular hydrogen bond with the carbonyl oxygen atom of the ethoxycarbonyl group at position 4 (8OCSCII21). On the other hand, the fourth isomer is the most stable in 4-phenylazopyrazolones (139), a chelated phenyl-hydrazone structure. 

Recently, it was shown that polydimethylcarbosiloxanes with a small content of side carbonyl groups (PDMS-C) exhibit increasing viscosity and formation of a physical network at elevated temperatures [88,89], This was attributed to a rearrangement of intramolecular hydrogen bonds, which formed between the carboxyls during the synthesis and isolation of the polymers, forming intermolecular hydrogen bonds. 

With (32), despite the intramolecular hydrogen-bonding possible in the enol form (326), the equilibrium lies essentially completely over in favour of the keto form (32a), because this can take up an anti-conformation in which the two electronegative oxygen atoms are as far from each other as possible, and in which the carbonyl dipoles are opposed. With (33), the C=0 groups are locked in the syn-con-formation in both keto (33a) and enol (336) forms, and the intramolecular hydrogen-bonding open to (336), but not to (33a), then decides the issue. 

In general, 1-substituted derivatives of anthraquinone are more bathochromic than the corresponding 2-substituted isomers, in accordance with PPP-MO calculations [1]. Intramolecular hydrogen bonding is not possible between the carbonyl group and a 2-... 

Moore et al. [189] showed that nalidixic acid has a strong intramolecular hydrogen bond between the acid proton and the ring carbonyl oxygen. This stabilized the molecule and weakened the acid (pKa 6.11). It is interesting in view of the previous photodegradation work that radical formation was most... 

H-donor for both the intramolecular hydrogen bond with the amide linker carbonyl the carboxylic acid group is deprotonated. 

A study of substituent influences on reaction of carbonyl compound (102) with trialkylallyltin (103) has established that high yield of allylation product (104) is obtained only when X = NO2 and R = OH (where R = Bu or Me and R = H or Me). The role of the intramolecular hydrogen bond in promoting rate enhancement and regioselective allylation (and reduction by HSnBus) of carbonyl compounds has been discussed. 

---