Carbonyl IR stretching frequencies

Following the trend towards lower carbonyl IR stretch frequencies, branching alpha to the amide carbonyl (Table 5, entries 53, 54, 62, 63 and 65) affects the shifts for mutagens and hydroxamic esters similarly and causes a marked downfield shift of up to 6 ppm relative to the acetamide substrate (Table 5, entry 60). These effects, as well as the smaller than expected downfield shift with ferf-butyl and neopentyl side chains are, as with the Ai-chlorohydroxamic esters, due to the combined influence of a stabilizing alkyl inductive effect together with destabilizing desolvation of the polar form of the amide carbonyl ". 

Table Stoichiometry and corresponding IR stretching frequencies of different metal carbonyls. Charges for monocarbonyls were estimated from the correlation between IR stretching frequency and charge of the metal center as inferred from theoretical calculations (for details see [15,17]) ...

The presence of two carbonyl conformers has also been observed (70MI5 84MI5) in the N-acyl derivatives of benzothiazolone 112 and benzooxa-zolone 113. In benzothiazolone derivatives 112, IR stretching frequencies... 

Table 10 EHT Calculated Carbonyl ir-Bond Orders (Pco) and IR Stretching Frequencies (78ijciA)64)...

The 111 NMR, 13C NMR (NMR - nuclear magnetic resonance), infrared (IR), ultraviolet (UV), and mass spectrometry (MS) data have been reported for the first example 5 of a 2/7-azepin-2-one (2-azatropone). The carbonyl group stretching frequency appeared at 1682 cm 1 in the IR spectrum of the neat material <2000JOC6093>. Further H and 13C NMR spectroscopic data on azepine derivatives have been summarized by Smalley <1997HOU(E9d)108>. 

The Infrared Region 515 12-4 Molecular Vibrations 516 12-5 IR-Active and IR-lnactive Vibrations 518 12-6 Measurement of the IR Spectrum 519 12-7 Infrared Spectroscopy of Hydrocarbons 522 12-8 Characteristic Absorptions of Alcohols and Amines 527 12-9 Characteristic Absorptions of Carbonyl Compounds 528 12-10 Characteristic Absorptions of C—N Bonds 533 12-11 Simplified Summary of IR Stretching Frequencies 535 12-12 Reading and Interpreting IR Spectra (Solved Problems) 537 12-13 Introduction to Mass Spectrometry 541 12-14 Determination of the Molecular Formula by Mass Spectrometry 545... 

The electron-withdrawing nature of a positive metal center should have the same effect on a n ligand as it would on a carbonyl group. The IR stretching frequency of a carbonyl (more accurately the force constant, k) is a reflection of the electronic interaction of the carbonyl group and the metal. Electron-poor metals (or metals also coordinated to n acids) do not backbond effectively to the carbonyl. Thus, the Lewis structure 17 makes a substantial contribution to the actual structure of the complex. 

---