Françoise Froment

Vibrational spectra and possible conformers of dimethylmethylphosphonate by normal mode analysis

Abstract A careful assignment of the i.r. and Raman spectra of CH 3 P(O)(OCH 3 ) 2 , CD 3 P(O)(OCH 3 ) 2 , CH 3 P(O)(OCD 3 ) 2 and CD 3 P(O)(OCD 3 ) 2 and a comparison with those of the parent molecules CH 3 OP(O)Cl 2 and CD 3 OP(O)Cl 2 suggest that only one conformer exists in the liquid state. This conformer is probably close to the most stable one calculated by CNDO/2 and ab initio STO-3G methods, with one CH 3 O group trans and the other cis to the PO group. The characteristic modes of the CP(O)(OC) 2 skeleton are analysed through a force field calculation. It is shown that the stretching vibrations of the single bonds PC and PO are strongly coupled. As already observed for carboxylic esters, it is shown that only mixed skeletal modes and mostly the bending modes are sensitive to the conformation of the methoxy groups around the PO single bond. On the other hand the v (PO) mode does not vary for the different conformers, and the extra components appearing in its vicinity, as well as in that of the v (PC) main vibrational mode, are best understood as being due to Fermi resonances with harmonic or combination tones coupling with these modes.

STRUCTURAL STUDY OF CARBANIONIC SPECIES FROM BIS(DIETHOXYPHOSPHONYL)-METHANE BY IR, RAMAN AND 1H, 31P, 13C NMR SPECTROSCOPIES

Abstract An IR and Raman study of the lithium associated carbanionic species 1 formed from bis(diethoxyphosphonyl)-methane in the solid state and in THF solution, as well as the IR and 1H, 31P, 13C NMR study of the potassium associated one in pyridine and dimethylsulfoxide are reported. A chelated symmetrical structure exists in the solid state and in associating medium. The central carbon is planar or nearly so from the NMR data. However, the negative value of 2 J PH in the anionic species raises the problem of estimating the various factors involved in the two bond coupling constants.

Effect of aggregation of nitrile anions on the 1,2 versus 1,4 regioselectivity towards benzylideneacetone

Abstract A direct evidence of the influence of aggregation state of lithiated phenylacetonitrile 1 on the 1,2 versus 1,4 regioselectivity towards benzylideneacetone 2 was established. Progressive addition of hexane to THF solutions raised the aggregates proportion of 1 as evidenced by IR νCN band and led to an increase of 1,4 adduct. Monomers afforded 1,2 addition in pure THF.

Formation of phosphonoacetate carbanions by lithiated bases or by the conjunction of a lithium salt and an amine: structural study of intermediate species

In THF, the anionic species (2) formed from methyl diethylphosphonoacetate (1b) by the action of Li bases coexist as aggregates (2A) and externally solvated monomeric ion pair (2M), while in CH3CN triple ions (2T) and small amounts of free ions (2–) are also characterized. When (1b) is in slight excess, relative to the lithiated base, these four species coexist in both solvents, together with other species (I). From n.m.r. and i.r. data, it appears that the intermediate species (I) include a neutral phosphonate (1b) moiety, as a Li+ cation bidentate ligand, the two other lithium solvation sites being occupied either by (2–), or by (1b) as a monodentate and a solvent molecule, or else by two solvent molecules. The structure of (1b) in this intermediate species is strongly perturbed as deduced from variations in 31P and 13C carbonyl shifts as well as that of νco. Furthermore, a fast proton exchange takes place between the anionic species (2) and free (1b) as shown by 1H n.m.r., but (I) does not participate in this exchange phenomenon. When (2) is formed by action of diazabicycloundecene (DBU) in the presence of LiCl, aggregates (2A), monomeric ion pari (2M), and small amounts of (2T) as well as two intermediate species (I) are characterized by i.r. or 31P n.m.r. spectroscopy. The role of DBU is manifold: it deaggregates LiCl or (2A), it deprotonates (1b) within (I), and it facilitates proton exchange between (2) and (1b), the relative importance of such effects depending upon the DBU concentration.