¹⁷O‐NMR‐Spektroskopie von Benzoylverbindungen YC₆H₄ COX: Empfindlichkeit auf Substituenteneinflüsse als Maß für den Elektronenmangel an der Carbonylgruppe

Abstract

Entgegen einer weit verbreiteten Meinung ist die 13C‐NMR‐Spektroskopie nicht zur Ermittlung von Elektronendichte am Carbonyl‐C‐Atom geeignet. Durch Messung der 17O‐chemischen Verschiebung bei aromatischen Carbonylverbindungen Y‐C6H4‐COX, X = CF3, H, CH3, CO2R, Br, Cl, F, OCOAryl, SR, OR, NH2, OH, O⊖, konnten jedoch verläßliche Aussagen über die Elektrophilie des Carbonyl‐C‐Atoms gemacht werden. Es ist beruhigend, daß die Ergebnisse in Einklang mit klassischen chemischen Regeln sind. Vieles spricht dafür, der 17O‐NMR‐Spektroskopie mehr Aufmerksamkeit zu schenken.

Influence of ortho substituents on 17O NMR chemical shifts in phenyl esters of substituted benzoic acids

“…[13,14] It was found that in methyl benzoates reaction series an introduction of electron-attracting substituents causes deshielding and electron-donating substituents shielding of the carbonyl and methoxy O atoms. [14][15][16] It has been shown [26][27][28][29] that in substituted carbonyl derivatives, Y-C 6 H 4 CO-X, RCO-X, the shielding of the carbonyl oxygen is increased and the sensitivity of the Y substituent is diminished with an increase in the electron-donating power of the X group.…”

The Chemistry of α-Haloketones and Their Utility in Heterocyclic Synthesis

“…On the scale of carbonyl electrophilicities, measured by 17 O-NMR spectroscopy [ 29 ], the presence of halogen atoms α- to the carbonyl group decreases the electron density around the oxygen atom ( Table 3 ) [ 29 , 30 ].…”

NMR of terminal oxygen. 9—17O NMR of the PO ‘double bond’: Phosphine oxides, phosphinates, phosphonates, acylphosphonates and related compounds

“…Both observations contrast with acet~phenones'*~ and point to the absence of resonance interaction between the aryl and the phosphoryl groups. Conclusive evidence shows that, in general, monosubstituted phosphinates such as ArHP(0)OR' (2) do not exist as the ArP(0H)OR' tautomers.' l b , I 3 In accord with this, our compounds show a strong P-H couplang (J = 550 Hz) and an IR signal at ca 2350 cm-', typical for P-H." Superficially, the formula of the phosphinate ester group P(=O)OR could be compared with that of a carboxylic ester, C(=O)OR.…”