Preferred inventive compounds are those wherein one or more of R1, R2, R3 or R4 is an alkyl group, and the remainder of R1, R2, R3 and R4 are H. A particularly preferred compound in accordance with the present invention is a compound of the formula (II) set forth above wherein R1 is methyl and ortho to F in formula (II), and R2, R3 and R4 are H.