Lactams ring strain

Thus, neither halogen substitution nor ring strain induces enzymatic hydrolysis. Molecules 21 and 22 may be bound in such a way that the (3-lactam carbonyl lies too far away from the catalytic serine hydroxyl group.72... 

Some information concerning ring strain and amide resonance can be obtained by comparing monocyclic and bicyclic /3-lactams. Monocyclic /3-lac-tams are very resistant to alkaline and acid hydrolysis [70] [71] due to reso-... 

Box 3.3 Effect of Ring Strain on the Carbonyl Stretching Frequencies of Lactones (Cyclic Esters) and Lactams (Cyclic Amides)... 

Much of the chemical reactivity of the /8-lactam antibiotics is associated with die /i-lactam moiety. The geometry and the accompanying increased ring strain results hr very little, if any. amide-resonance stabilization leading to a marked increase in chemical reactivity when compared to a normal amide. In fact, in many instances the reactivity of the lactam carbonyl is... 

Cyclic amides are called lactams. A Creek letter is assigned to tire lactam to denote size, (i-lactams are 4-membered rings, y-lactams have 5 members, 5-lactams have 6 members, and so on. Although amides are the most stable of the carboxylic add derivatives, pdactams are highly reactive due to large ring strain. Nucleophiles easily react with (Mactams. p-lactams are found in several types of antibiotics. 

The anionic polymerizability of 67 is much lower than that of 58. This difference is due not only to the lower ring-strain of 67 and but also to a greater steric hindrance that the lactam anion of 67 receives when it comes closer to the carbonyl... 

Lactones and Lactams Unstrained lactones (cyclic esters) and lactams (cyclic amides) absorb at typical frequencies for esters and amides. Ring strain raises the carbonyl absorption frequency, however. Recall that cyclic ketones with five-membered or smaller rings show a similar increase in carbonyl stretching frequency (Section 18-5A). Figure 21-5 shows the effect of ring strain on the C=0 stretching frequencies of lactones and lactams. 

Ring strain in a lactone or lactam increases the carbonyl stretching frequency. 

Biological Reactivity of /8-Lactams /3-Lactams are unusually reactive amides and are capable of acylating a variety of nucleophiles. The considerable strain in the four-membered ring appears to be the driving force behind the unusual reactivity of /3-lactams. When a /3-lactam acylates a nucleophile, the ring opens and the ring strain is relieved. 

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