Silylation of substituted benzhydroxamic acids: NMR spectra (13C, 15N and 29Si) and structure of tert-butyldimethylsilyl derivatives

✍ Scribed by Jan Schraml; Magdalena Kvičalová; Ludmila Soukupová; Vratislav Blechta; Otto Exner

• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 72 KB
• Volume: 12
• Category: Article
• ISSN: 0894-3230
• DOI: 10.1002/(sici)1099-1395(199909)12:9<668::aid-poc175>3.0.co;2-c

✦ Synopsis

Twelve para-and meta-substituted benzhydroxamic acids were subjected to exhaustive silylation with N-(tert-butyldimethylsilyl)-N-methyltrifluoroacetamide (with 1% of tert-butyldimethylsilyl chloride as a catalyst). In all cases only one product was isolated. According to the assigned NMR spectra ( 13 C, 15 N, and 29 Si), the product is the Z-O 1 , O 4 -bis(tert-butyldimethylsilyl) derivative of substituted benzhydroximic acid, independently of the nature of the para or meta substituent. For structure determination, the 29 Si shifts and 1 J( 13 C, 13 CN) coupling constants are decisive. The chemical shifts ( 13 C, 15 N, 29 Si) show dependences on the substituent constants of various kinds: even the 13 C shift of the sixth atom from the benzene ring varies with substitution. The 13 C and 15 N chemical shifts of the C=N moiety exhibit opposite dependences on the substituent; the 29 Si shifts of the two silicon atoms are almost equally sensitive to the substituent effects despite their different distances from the substituent.