5-lactone hydrogen bond

A search for intermolecular bonds resulted in one possible hydrogen bond between hydroxyl 013 and lactone carbonyl Ol. The distance between 01 and 013 is 2.85 A, a value well within the range expected for OH-O hydrogen bonds (25). The hydrogen atom position for hydroxyl 013 was chosen to be along the 013-01 vector. The hydrogen position was not evident in the difference electron density map, presumably due to problems modeling the 013 position. 

A mechanistic rationale for the observed cw-selectivity has been proposed based on preorganisation of the Breslow-type intermediate and imine through hydrogen bonding 253, with an aza-benzoin oxy-Cope process proposed. Reaction via a boat transition state delivers the observed cw-stereochemistry of the product (Scheme 12.57). Related work by Nair and co-workers (using enones 42 in place of a,P-unsaturated sulfonylimines 251, see Section 12.2.2) generates P-lactones 43 with fran -ring substituents, while the P-lactam products 252 possess a cw-stereo-chemical relationship. 

In some cases it is possible to differentiate between the various alkyl substituents. Primary, secondary and tertiary nitrates and nitrites all show clearly different infrared absorptions. The spectra of acid fluorides can be used to differentiate chain-end groups from pendant acid groups. Furthermore, the loss of all -OH species upon sulfur tetrafluoride exposure allows the reliable estimation of ketones, esters and lactones without the complication of hydrogen-bonding induced shifts in the spectra. Preliminary results from the use of these reactions to characterize y-ray oxidized polyethylene and polypropylene are used to illustrate the scope of the methods. 

The infrared spectrum of erythromycin is commonly used for its identification. Figure 2 shows the spectrum of a 75 mg./ml. chloroform solution. The bands at 1685 and 1730 cm- are due to the ketone carbonyl and the lactone carbonyl, respectively. The absorption peaks between 1000 and 1200 cm-1 are due to the ethers and amine functions. The CH2 bending is evidenced by peaks between 1340 and 1460 cm-, and alkane stretching peaks appear between 2780 and 3020 cm-. Hydrogen bonded OH and water appear as bands between 3400 and 3700 cm-1. 

P2j Z = 4 Dx = 1.357 R = 0.048 for 1,989 intensities. The crystal structure contains two symmetry-independent molecules having almost the same conformation. The lactone rings are planar the conformation of the dioxolane ring in one is close to an envelope, and that in the other has a twist conformation. The linkage between the rings, as defined by 0-4-C-4-C-5-0-5, is -65 and —75°. The two independent molecules are hydrogen-bonded into dimers by the two N—... 

This provides a cyclic transition state in which hydrogen bonding can enhance the reactivity of the carbonyl group.119 120 Excellent yields of large-ring lactones are achieved by this method. 

The furanoid ring is nonplanar. All of the oxygen atoms, except 0-1 and 0-4 of the lactone group, participate in hydrogen bonding (see formula 6). 

Intramolecular lactonization has been studied on cobalt(III) complexes (Scheme 44).144 The reaction is catalyzed by general acid and the attack of coordinated water occurs at a greater rate than that of coordinated hydroxide ion. Presumably, the relatively non-nucleophilic water is assisted by hydrogen bonding to the carboxyl group to become a pseudo-hydroxide ion. 

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