[throllen]

how come the steric influence of the methoxy group on substituion pattern of anisole is so different from the N-acetyl group on the acetanilides'? Someone told me it can't be their sizes... but what else?  Could it be the extra oxygen in the acetanilide?

[agrobert]

The pattern is not different they are both ortho para directors but to different degrees.  Draw resonance structures for EAS on the ortho position for anisole and acetanilide.  Try building a model to see what role size may play.

[macman104]

how come the steric influence of the methoxy group on substituion pattern of anisole is so different from the N-acetyl group on the acetanilides'? Someone told me it can't be their sizes... but what else?  Could it be the extra oxygen in the acetanilide?

Why would they say it cannot be their size?  They are quite different in size, and the N-acetyl group should hinder substitution at the ortho position more than the methoxy group (pretty sure).

Also, correct me if I'm wrong, but isn't the electron-donating ability of the N-acetyl group weakened by the carbonyl?  The carbonyl and the aromatic ring are going to be competing for the lone pair of the nitrogen, whereas, the methyl, in the methoxy, is simply going to be pushing electrons toward the oxygen making it an even strong electron-donor into the ring.

[sjb]

The pattern is not different they are both ortho para directors but to different degrees.

Arguably wordplay, but the pattern is different then, as the ratio of ortho to para product is different