19FNMR

Figure 16. 19FNMR of (R)-Mosher amide of (S)-alanine containing 0.12% of (R)-Mosher amide of (R)-alanine. 

The rate of ring inversion of pentafluoro-l,2-oxazetidine as determined by 19FNMR is very fast ( a=4.2 kJ mol-1), with the nitrogen inversion barrier much higher (70JOC927, 1607). 

Another compound that is relatively easy to make with solution-phase fluorination is per-fluorocongressane (11) (19FNMR data and an X-ray structure are available).26... 

Difluoro(diethoxyphosphinyl)acetyl chloride (7) is characterized by its conversion to the unstable difluoro(diethoxyphosphinyl)acetyl fluoride (8) by treating with potassium fluoride.31 Both compounds have been analyzed by 19FNMR spectroscopy. 

The stereochemistry was determined from the relative intensities of 19FNMR signals. 

To a solution of 1-substituted pentafluorobenzene derivative (2 mmol) in CH2C12 (4 mL) in a Kel-F vessel was added XeF2 (338.6 mg, 2 mmol) at 25 C, and, with stirring, anhyd BF3 (trace amounts) was introduced into the mixture. After 10-30min, Xe (g) evolution ceased and the reaction appeared to be complete. The solvent was partially removed by distillation under reduced pressure, the crude mixture was analyzed by 19FNMR, and the products were isolated by preparative GC. 

A series of [M(02)F3(diket)] complexes has been prepared by the reaction of /3-diketones with [M(02)F4(H20)] . 3H and 19FNMR spectra indicate that the products exist as a mixture of geometrical isomers in MeCN. The reaction of oxalic acid with [Nb(02)F4(H20)] yielded [Nb2(02)2F6(C204)]z. A bridging oxalato group and a coordination number of seven for the metal were proposed. [M(02)F3(phen)], [M20(02)F4(bipy)2] and [M(02)F3(0AsPh3)2] were obtained when the neutral ligands were allowed to react with [M(02)F4(H20)] . 

The 19FNMR (CFC1,) of IV exhibits four peaks for each isomer. Isomer A 687.3 [center AB system, J(1A,1B)=228 Hz, relative peak area 2,2F,CF,(1)], 161.3 [septet, J(2,5)=18 Hz, relative peak area 1, 1F,TF(2)], 193.6 [doublet of quartets, J(3,5)=56 Hz, relative peak area 1,1F,CF(3)], 86.0 [center AB system, J(1A,1B)=228 Hz, relative peak area 2,2F,CF,(4)]. Isomer B 6 84.1 [coalesced AB system, relative peak areaz,2F,CF (l)], 165.7 [complex singlet, relative peak area 1,IF,CF(2)], 195.4 [doublet of sextet, J(3,5)=54 Hz, relative peak areal.lF.CF O)], 84.4 [center AB system, J(1A,1B)=231 Hz, relative peak area 2,2F,CF,(4)]. The GC-mass spectral data of IV show two species, which Tiave different elution times but with identical parent ions at 304(C7FgH,QS3 ) and the same mass fragments. These results 1ndi cate tnactnere are two isomers in IV. 

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