Acid chlorides contributing structures

Problem 2.43 Arrange the contributing structures for (a) vinyl chloride, H,C=CHC1, and (h) formic acid, HCOOH, in order of increasing importance (increasing stability) by assigning numbers starting with 1 for most important and stable. 

The (2 + 2)-cycloaddition reactions of ketenes with heterocycles via an endocyclic imino group have contributed substantially to the synthesis of penicillin (92a) and cephalosporin C (93a) antibiotics and structurally related heterobicyclic /Mactams.7 11 Reactions with relatively stable ketenes, e.g., diphenylketene, have been reported as well as reactions of heterocycles with mixtures of acid chlorides and tertiary amines. 

The formation of acyl halide-Lewis acid complexes have been observed by several methods. For example, both 1 1 and 1 2 complexes of acetyl chloride, with AICI3 can be observed by NMR spectroscopy. The existence of acylium ions has been demonstrated by X-ray diffraction studies on crystalline salts. For example, crystal structure determinations have been reported for /i-methylphenylacylium and acetylium ions as SbFg salts. There is also a good deal of evidence from NMR measurements which demonstrates that acylium ions can exist in nonnucleophilic solvents. " The positive charge on acylium ions is delocalized onto the oxygen atom. This delocalization is demonstrated in particular by the short O—C bond lengths in acylium ions, which imply a major contribution from the structure having a triple bond ... 

Other disinfectants include quartemary ammonium compounds (QACs) such as benzalkonium chloride (BACl) and didecyldimethylammonium chloride (DDMAC). Disinfectants have been shown to denitrifying bacteria at concentrations as low as 1-2 ng L (Kiimmerer, 2004b). QACs are specifically not used for disinfecting clothing, but their use is central in other purposes. Triclocarban and triclosan have an aromatic structure that is rich in chlorides, which contribute to their persistence in the environment. QACs are also quite persistent in the environment (Al-Ahmad et al., 2000). Other disinfectants include chloramines and 1,3-dichlorosucyanuric acid as well as PVP-iodide-based disinfectants. 

Most polysaccharides used today are of plant origin. However, also bacteria produce polysaccharides. Especially extracellular polysaccharides (eps s) produced by lactic acid bacteria may find application in foods. Lactic acid bacteria are food-grade organisms and the eps s produced offer a wide variety of structures. The presence of eps is considered to contribute greatly to texture and structure of fermented milk products. An exopolysaccharide produced by Lactococcus lactis ssp. cremoris B40 was chosen as a subject of study. The eps was a gift from the Dutch Institute of Dairy Research (NIZO), Ede, the Netherlands. The eps had no gelling properties, could not be precipitated in plates by ethanol or cetylpyridinium chloride and did not show interaction with Congo red. 

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