polymer crystallized from melt or solution [1OJ. Occasionally a less stable or low temperature structure can be produced. An example is the polycaprolactam made by zone polymerization which has not the ideal orthorhombic crystal structure, but a paracrystalline structure which has a less perfect alignment of Hbonds[331. The metaphosphates can be produced in a low temperature crystal form first which converts into the high temperature modification at higher temperature 31. Polyoxymethylene may under certain conditions of crystallization during polymerization form orthorhombic instead of hexagonal crystals 1121. Poly-p-xylylene also crystallizes during polymerization first as a metastable orthorhombic structure, to change at about 240 "C into the stable, denser hexagonal crystal structure "91.

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Rearrangement and cyclization of a series of p-nitrophenyl and heteroaryl thiohydrazonates ArSCAr′ = NNHC6H3XY(2,4), where the displaced substituent X is Br or F and the remaining substituent Y is Br or NO2, occurs under suitable basic conditions to the corresponding 7-substituted 2-aryl-4-p-nitrophenyl- and -4-heteroaryl-4H-1,3,4-benzothiadiazines, e.g. 13 → 19. Under these or suitable acidic conditions, the 4,6-dimethyl-2-pyrimidinyl thiohydrazonate rearranges to the thiohydrazide Ar′CSNHNArC6H3XY(2,4), apparently the first case of thiohydrazonate thiohydrazide rearrangement; such acidic treatment produces cleavage of some other heteroaryl thiohydrazonates.Independent syntheses of two of the 4-heteroaryl-substituted benzothiadiazines are reported.

Die Reaktion von Kaliumphthalimid mit Halogenalkanen und mit vielen anderen AlkyIierungsmitteln fuhrt zu N-Alkylphthalimiden, die durch Hydrolyse oder Hydrazinolyse in primcire Amine umgewandelt werden k8nnen. Anwendungsbereich und Grenzen dieser Reaktionen, die unter dem Namen Gabriel-Synthese bekannt sind, werden in diesem Aufsatz besprochen.

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