Hot homolytic aliphatic and aromatic substitution S/sub HH/$sup 2$

Book · Mon Jan 01 04:00:00 EST 1973

OSTI ID:4368942

Machulla, H J; Stoecklin, G

The pressure dependence of the stereochemical course in hot homolytic T- for-H and /sup 38/Cl-for-Cl substitution in meso and racemic 1,2-dichloro-1,2- difluoroethane has been studied from about 10 to 10/sup 4/ torr. For both recoil tritium and chlorine, substitution with inversion of configuration is almost negligible in the gas phase and its yields remain constant over the entire pressure range studied. Typical pressure effects are observed, however, for substitution with retention of configuration, somewhat depending on the system. While the change from the high pressure gas phase to the liquid leaves T-for-H substitution almost unaffected, /sup 38/Cl-for-Cl substitution exhibits strong phase effect. Pressure, phase (density) and moderator dependence of /sup 38/Cl- for-F and /sup 38/Cl-for-H substitution has also been studied in fluorobenzene. The density dependence in aromatic systems is completely different from in aliphatic systems, i.e., the drastic yield-increase accompanying the high pressure gas to liquid phase change is not observed. The isomer distribution is independent of the moderator concentration and is not affected by pressure and only very little by phase changes. Together with the previously reported conformational effect, the results provide information on the problem of direct reaction versus complex formation. While in aliphatic systems complex formation in S2/sub HH/, if at all, seems to occur in the liquid phase only, hot homolytic aromatic substitution proceeds via pi sigma -complex formation already in the gas phase. (GE)

• Research Organization: Kernforschungsanlage, Juelich, Ger.
• NSA Number: NSA-29-007595
• OSTI ID: 4368942
• Country of Publication: Germany
• Language: English

Related Subjects

*CHLORINATED ALIPHATIC HYDROCARBONS-- HOT ATOM CHEMISTRY
*CHLORINE 38-- HOT ATOM CHEMISTRY
*FLUORINATED ALIPHATIC HYDROCARBONS-- HOT ATOM CHEMISTRY
*FLUORINATED AROMATIC HYDROCARBONS-- HOT ATOM CHEMISTRY
*TRITIUM-- HOT ATOM CHEMISTRY
AROMATICS
CHLORINE
CONFIGURATION INTERACTION
DENSITY
HYDROCARBONS
ISOTOPIC EXCHANGE
N40410* --Chemistry--Radiochemistry & Nuclear Chemistry--Hot Atom Chemistry
ORGANIC CHLORINE COMPOUNDS
ORGANIC FLUORINE COMPOUNDS
ORGANIC MODERATORS
PRESSURE DEPENDENCE
RECOILS
STEREOCHEMISTRY