Claude Decoret

A theoretical study of the first order γα and αβ phase transitions of p-dichlorobenzene

Abstract A theoretical study of the γue5f8α and αue5f8β phase transitions of p-dichlorobenzene with the aim of elucidating the effect of crystal forces on these transitions is presented. Our calculations are in agreement with experience concerning the necessities of microactivities for the nucleation. The Monte Carlo technique efficiently simulates the growth of the nucleus since the final positions of the molecules correspond to the positions given by the crystal structure with a statistical weight of about 30–40%.

Theoretical study of organic solid state reactivity: Isomerisation of cyclohexadienones

Abstract Microscopic observations of the photochemical rearrangement of 2,4,6,6-tetrachloro-3-methyl-5-isopropylcyclohexa-2,4-diene-1-one 1 into 2,4,4,6-tetrachloro-3-methyl-5-isopropylcyclohexa-2,5-diene-1-one 2 are reported. Parallel to experimental results MNDO calculations have been performed on models corresponding to the isolated molecules 1 and 2. Theoretical calculations on packing energy of crystals of 1 and 2 lend support to the molecular mechanism occurring in the solid state.

Structure and Solid Hydrolysis of 3, 1-Benzoxazin-4-Ones

Abstract Solid hydrolysis of 2-substitued 3, 1-benzoxa-zin-4-ones are presented. O18 experiments with labelled water and hydrolysis in acidic conditions show the reaction occurs on >C=N- function. A protonated intermediate for the reaction is proposed. Theoretical calculations are in agreement with the assumed intermediate.

A Study of the Mechanism of Hydrolysis of Single Crystals of 2-Phenyl-4H-3, 1-Benzoxazin-4-One

Abstract Single crystals of 2-phenyl-4H-3,1-benzoxazin-4-one,1,(a = 13.315 A, b = 3.912 A, c = 20.465 A, β = 94.93°, Z = 4, P21/n, R = 0.047) have been found to undergo hydrolysis at room temperature. Reacting single crystals were observed to react first at needle ends of crystals with the reaction proceeding along the b axis of the needle. The chemical mechanism and the reaction pathway in the solid is rationalized by chemical results (analysis of mass spectra resulting from 180 water experiments) and theoretical calculations based on the X-ray data. Evaluation of occupied and free-space in crystal 1 is obtained by the method of Gavezzotti.

Experimental and Theoretical Study of Organic Solid State : Structure and Reactivity

Abstract Three of our recent attempts to study the mechanism of organic reactions in the solid phase are presented. The stability of organic crystals of monotropic polymorphic substances is studied. Also described are the rearrangement of orthocyclohexadienone into paracyclohexadienone and the solid state hydrolysis of acetylanthranyl. In all cases it is shown that organic single crystals are useful for the study of reaction mechanisms.

Isomerisation of Molecules in Organic Crystals, A Theoretical Study

Abstract The effect of the minimization of crystal energy on the rearrangement in the solid state of orthocyclohexadienone 1 into paracyclohexadienone 2 is investigated using a combination of theoretical lattice energy and quantum chemical calculations. Lattice energy calculations show the crystalline structure of para-dienone 2 to be less stable than the crystalline structure of ortho-dienone 1. On the contrary concerning the energies of isolated molecules the para-dienone 2 is more stable than the ortho-dienone 1. Such an approach including crystal energetic calculations and energetic analysis of isolated molecules promises to be useful in the investigation of the chemical pathway for the rearrangement in the solid state.

Conformational analysis of the four 3-methyl-isopropylphenol isomers (thymols) by molecular orbital calculations and X-ray crystal structure determinations

Abstract PCILO calculations have been used in a conformational investigation of 3-methyl- x -isopropylphenols (thymol isomers), including a study of the barrier to internal rotation of substituents. The results of the calculations are in good agreement with those available from experimental crystal structure determinations, except for 3-methyl-6-isopropylphenol. For the latter the calculated most stable conformer cannot form a crystal with hexamers bonded by H bonds, as is determined by crystallography. The heights of the barriers to internal rotation of the substituents are compared with the available experimental data and discussed in terms of steric hindrance.

Reaction Gaz-Solide Organique. Hydrolyse De Benzoxazinones et Naphtoxazinones

Abstract This communication reports the study of the reactivity of single crystals of benzoxazinones 1 and 2 and naphtoxazinones 3 and 4. Single crystals 1, 2 and 4 react anisotropicly while single crystal 3 reacts randomly. The crystalline structures of 3 and 4 have been determined. The experimental results are rationalized by the use of the program of Gavezzotti and the program of Caillet and Claverie.

Calculation of vibrational frequencies of α para-dichlorobenzene crystal

Abstract Vibrational frequencies of an α para-dichlorobenzene crystal are calculated. By solving an inverse spectral problem, the series of force constants of an isolated p-C6H4Cl2 molecule were found. It was shown that this series can be carried over to the crystal model. This means that during crystallization, the electronic structure of a p-C6H4Cl2 molecule stays constant. Intermolecular interaction was modeled upon pseudo-bonds. Force constants were estimated from the calculation of intermolecular interaction energy, by the way of a Monte-Carlo simulation. Vibrational dynamics of the crystal and isolate molecule were analyzed. Absorption bands sensitive to the crystallization of the molecule were found.

Langmuir Monolayers of p-Octadecylbishomooxacalix[4]Arene

Langmuir-Blodgett (LB) monolayers of p-octadecylbis homooxacalix[4]arene & were formed at the air-water interface, in the presence of sodium hydroxide, with a solid state packing. The structure of the solid state was investigated by X ray diffraction techniques and the molecular packing was modeled by minimum energy calculations