Über die Struktur der Thioamide und ihrer Derivate, XII¹⁾ Untersuchungen zur behinderten Rotation bei Thiohydroxamsäuren

Abstract

Eingegangen am 26. Mai 1970 0.N-Dialkyl-hydroxylamine 4, darunter auch die 0-Methyl-N-phenyl-Verbindung 4f, deren Darstellung bisher vergeblich versucht wurde, lassen sich zu N-Alkyl-thiohydroxamsaureestern (5, 6b und 7) thioacylieren. Im Gleichgewicht der Thiohydroxamsaureester ist die ( E ) -Form bevorzugt, auBer wenn diese Form sterisch nicht moglich erscheint (5e). Die Begiinstigung des (E)-Isomeren wird durch elektrostatische Effekte erklart. Wie sich in den freien Aktivierungsenthalpien der behinderten Rotation, den Fernkopplungskonstanten iiber die partielle C-N-Doppelbindung und der Lage der Thioamid-B-Banden dokumentiert, ist in der Thiohydroxamsaure 6 a bzw. den Estern 5, 6b und 7 (Formhydroxamsauren und -ester 8)die Elektronendichte der C-N-Bindung geringer als in Thioamiden (Amiden), wofiir der induktive Effekt der Hydroxy-bzw. Alkoxy-Gruppe verantwortlich ist.On the Structure of Thioamides and their Derivatives, X W ) .

The thiohydroxamate system

“…The free activation energy during rotation about the C N bond is higher by 4.3 kcal/mol than in hydroxamic acids [1]. Simple thiohydroxamic acids have pK a values from 4.2 to 5.6 compared to a pK a of the order of 9 for the corresponding hydrox-amic acids [1].…”

Substituent effects on 15N NMR chemical shifts in selected N‐alkylthiohydroxamic acids. A comparative study

“…As we established by means of a cursory analysis of lowtemperature 1 H spectra, at room temperature the mutual E-Z A typical barrier for rotation around the C-N bond in acetothiohydroxamic acids is higher (20.0 kcal mol 1 , T c 87°C). 7 As we predicted, all substituents on the nitrogen in THAs, i.e. alkyl, hydroxyl and thiocarbonyl groups, cause 15 A characteristic feature of the investigated hydroxylamine derivatives is the non-additivity of all substituent increments, which makes it impossible to apply additivity rules for predicting the 15 N chemical shifts.…”

Antibiotic Action of N -Methylthioformohydroxamate Metal Complexes

“…Thioformin was prepared by procedures described previously (2,6,17). Metal complexes of thioformin were prepared as described previously (6); O-methylthioformin (N,O-dimethylthioformohydroxamate) was prepared from 0-ethylthioformate and N,O-dimethylhydroxylamine by a previously described procedure (19), as was N-methylformohydroxamic acid (18). Tris(N-methylformohydroxamato)iron(III) was prepared frorti N-methylformohydroxamic acid and excess FeCl3*6H20 in aqueous solution and purified by benzyl alcohol extraction (13 (6).…”