STRUCTURAL EFFECTS IN SOLVOLYTIC REACTIONS .42. EFFECT OF INCREASING ELECTRON DEMAND ON THE C-13 NUCLEAR MAGNETIC-RESONANCE SHIFTS FOR SUBSTITUTED 9-METHYL-9-ANTHRACENIUM CATIONS - EVIDENCE FOR THE UNIMPORTANCE OF STERIC HINDRANCE TO CO-PLANARITY IN CAUSING ANOMALOUS C-13 NUCLEAR MAGNETIC-RESONANCE SHIFTS