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Sterically stabilized alpha-lactams react by two distinct acid-catalyzed pathways. Protonation on oxygen results in nucleophilic attack at the acyl carbon and gives C-2 products. Protonation on nitrogen leads to nucleophilic attack at the C-3 carbon and yields C-3 products. The mechanism thus developed is very useful for understanding the changes in rates and product distributions in the reactions of sterically stabilized alpha-lactams with nucleophiles. It can also be extrapolated to other alpha-lactams so that a more coherent picture of alpha-lactam reactivity can be developed. 相似文献
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This paper discusses neighborhood search algorithms where the size of the neighborhood is “very large” with respect to the size of the input data. We concentrate on such a very large scale neighborhood (VLSN) search
technique based on compounding independent moves (CIM) such as 2-opts, swaps, and insertions. We present a systematic way
of creating and searching CIM neighborhoods for routing problems with side constraints. For such problems, the exact search
of the CIM neighborhood becomes NP-hard. We introduce a multi-label shortest path algorithm for searching these neighborhoods
heuristically. Results of a computational study on the vehicle routing problem with capacity and distance restrictions shows
that CIM algorithms are very competitive approaches for solving vehicle routing problems. Overall, the solutions generated
by the CIM algorithm have the best performance among the current solution methodologies in terms of percentage deviation from
the best-known solutions for large-scale capacitated VRP instances. 相似文献
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