François Crasnier

On the conformational analysis of (CH3)3M (M = N, P, CH, SiH) molecules: CNDO/2 calculations versus experimental data. LEM or calder conformation?

Abstract CNDO/2 calculations are performed for the homogeneous series of (CH 3 ) 3 M compounds (M = N, P, CH, SiH) in order to determine the molecular equilibrium conformation. In agreement with available experimental data for the amine, the phosphine and the silane, the theoretical energy minimum is found for the (60, 60, 60) - so-called LEM - conformation in which each methyl group is staggered with respect to the two opposite (MC) bonds. The same LEM conformation is predicted to be theoretically preferred for the isobutane molecule, this result being very sensitive to the “C 3V or not” quality of the methyl groups. The values of optimized CMC angles, rotational barriers and dipole moments are well reproduced.

Theoretical conformational analysis of lewis adducts: II. CNDO/2 Calculations versus microwave data for methylphosphine borane, (CH3)H2P·BH3

Abstract The electronic structure and preferred conformations of (CH 3 )H 2 P · BH 3 are investigated within the framework of the CNDO/2 approximation. In complete agreement with microwave data, the (180, 180) conformation. Fig. 1, is predicted to be the only stable conformation. The barriers to internal rotation along the (P-C) and the (P-B) bonds are 3.3 and 3.4 kcal/mole, respectively. Bicentric energy partitioning shows that the variations of the total energy are mainly reflected by variations of the spatial interaction energy between phosphorus and the six hydrogens of the CH 3 and BH 3 groups.

Analyse conformationnelle et structure électronique de la phosphinodifluorophosphine, PH2-PF2

Abstract The electronic structure and conformational analysis of H 2 P-PF 2 are investigated within the framework of the CNDO/2 approximation. Preferred gauche (θ = 65°) and trans (θ = 180°) conformations are predicted, the latter being the only actual one (ΔG° = 4.5 kcal mole −1 ), in perfect agreement with microwave data. Bicentric energy partitioning shows that the variations of the total energy

Analyse conformationnelle theorique des complexes acide-base de lewis: III. Une approche semi-empirique (méthode CNDO/2) des geométries et de l'analyse conformationnelle du borazane et de ses dérives perfluoré

Abstract The optimized geometries and theoretical data from conformational analysis cf borazane and its perfluoro derivatives are investigated within the framework of the CNDO/2 approximation. The effect that fluorination has on the geometrical and electronic parameters of the investigated series of compounds is pointed out and the authors offer an explanation for the anomalous behaviour of H 3 N.BF 3 . Furthermore, it is shown that the assumption of tetragonal hybridization for the N and B atoms of any borazane is incorrect if the F 3 N molecule is used as the Lewis base.

On the Scent of Dandelion Dendrimers. Part I. Cyclophosphazenic Hexapodanes as New Cores

Abstract Aminolysis of N3P3Cl6 by long-chain diamines, H2N—(CH2) n —NH2 (n  6), leads regiospecifically to hexadangling (or hexapodanes) monomeric species provided it was achieved on alumina impregnated with potassium hydroxide. These reactions run instantaneously at room temperature. Such hexapodanes constitute starting materials (cores) for future design of spherical (i.e. aesthetically similar to dry dandelion flowers) cyclophosphazenic dendrimers.

Analyse conformationnelle de l'aminodifluorophosphine H2N-PF2 et de la diméthylaminodifluorophosphine (CH3)2N-PF2: Une analyse critique des données expérimentales

Abstract The inconsistency which was recently observed in the conformational analysis experimental data on H 2 N-PF 2 and (CH 3 ) 2 N-PF 2 molecules is investigated within the framework of the CNDO/2 approximation. The X-ray determination made by Nordman and Morris on the latter molecule seems to be the most realistic. However, it was impossible to select the actual set of experimental parameters amongst the various works dealing with the conformational analysis of H 2 N-PF 2 . It seems that, in such conditions, a semi-empirical approach like the CNDO/2 procedure could be considered as a method of solving problems of conformational analysis in highly localized systems.

Analyse conformationnelle théorique et structure électronique de la tritertiobutylphosphine

Abstract An optimized geometry of tri-tert-butylphosphine is determined within the framework of the CNDO/2 approximation: d (C-C) = 1.548 A (fixed), d (C-H) = 1.111 A (fixed), d (P-C) = 1.846 A, ∠CCC = 112.1°, ∠CCH = 113.1°, ∠CPC = 108.2°. The ∠CPC value is similar to the empirical data (109°) deduced by Schmutzler from NMR measurements. Moreover, the three (t-C 4 H 9 ) groups (which are in the Calder form) are involved in a molecular gearing defined by a 36 o twist angle around the (P-C) bonds.

Megastigmane and Iridoid glucosides from Avicennia Germinans: Two Isomeric Forms of an Iridoid

Abstract The iridoid 2′-coumaroyl mussaenosidic acid, isolated from Avicennia germinans (Avicenniaceae), was analysed by NMR and molecular modeling: two isomeric forms were confirmed. In addition, the known compound 1 (6S, 9R) roseoside was isolated for the first time from this species of Avicennia.

ON THE SCENT OF SPHERICAL DENDRIMERS : CYCLOPHOSPHAZENIC DANDELION DENDRIMERS UP TO THE EIGHTH GENERATION

Abstract Preparation of spherical dendrimers up to the eighth generation from D3h cyclophosphazenic hexadangling cores (coded as sexapus) involves two repetitive steps: aminolysis of hexachlorocyclotriphosphazene, N3P3Cl6 0, by long-chain aliphatic diamines (such as 1,6-Diaminohexane and higher cousins) leading to sexapus cores with dangling diamino groups followed by a grafting of N3P3Cl5 flagstones as 5-fold growing multipliers on these amino endings. Dendrimers of the first (compounds 1a, b) to the eighth (compounds 8a, b) are described. Dendrimer of the eighth generation, 8b, possesses 2,343,750 terminal (P-Cl) functions (molecular weight 228,977,179).

Analyse conformationnelle théorique des complexes acide-base de lewis: VII1. Le cas de la molécule de triméthylphosphineborane, (CH3)3P · BH3

Abstract The conformational analysis and the electronic structure of the trimethyl-phosphine-borane Lewis adduct are investigated within the framework of the CNDO/2 approximation. The methyl groups take up the Lem conformation and and the whole molecule is staggered with respect to the P · B bond. The rotational barriers around the P · B and P-C bonds are respectively 4.09 and 3.83 kcal mole −1 . Their origin is due to the spatial energy interaction terms between the phosphorus atom and the 12 hydrogens. The computed value of the dipole moment (6.0 D) matches the two available experimental data.