
TY  - JOUR
A1  - Ho, KC 
A1  - Miller, J 
T1  - The SN mechanism in aromatic compounds. XXXII. Reactivity of some perhalogenobenzenes
JF  - Australian Journal of Chemistry
JO  - Aust. J. Chem.
Y1  - 1966
VL  - 19
IS  - 3
SP  - 423
EP  - 436
KW  - 
UR  - https://doi.org/10.1071/CH9660423 
N2  - Substituent effects in a series of pentafluorophenyl compounds (C6F5X) ranging from powerful activating to powerful deactivating substituents are considered, both as regards orientation and rates, and shown to be simply and reliably predicted by considering the change as made up of two components, viz. from C6F6 to C6F5H and from C6F5H to C6F5X. The same principle applies generally to C6Hal5X compounds, and the necessary orientation and rate data are obtainable from the existing large body of substituent effects in aromatic SN reactions. Comparisons are thus also easily possible with substituent effects in aromatic SE reactions, and more generally. The reasons for predominant para direction for almost all groups, except the more powerful deactivating substituents which are meta directing, and the expectation of a few borderline cases, emerge clearly from discussion.   While orientation is largely known already, there have been very few precise rate determinations apart from the present work.   Some brief consideration of the admixture of dioxan with protic solvent is given.   The reactivities of hexafluorobenzene and hexachlorobenzene are compared. The substantially greater reactivity reported with the former is regarded as due solely to the greater mobility of fluorine than chlorine, with first row nucleophdes in protic solvents; whereas in contrast it is predicted that the C6Cl5 group is slightly more activating for aromatic S, reactions than the C,F, group.   The relative reactivities of C6F6 and C6H5F, and C6Cl6 and C6H5Cl are also compared. Rate ratios are c.108; &#916;&#916;E? c.15 kcal mole-1; and &#916;log10B c.+1. 
ER  -

