SUBSTITUENT-INDUCED CHEMICAL-SHIFTS ALONG C=C DOUBLE-BONDS

H-1 and C-13 NMR signals were assigned and CH coupling constants (1J, 2J, 3J) determined for a series of alpha-mono- and alpha,alpha-disubst ituted (1,1,3,3-tetramethyl-2-indanylidene)methanes with the following alpha-substituents: (mesityl)2B, n-propyl, phenyl tert-butyl-C(=NH), cyano, (tert-butyl)2C(OH), pivaloyl, H2N-CO, PhNH-CO, carboxy, nitro, acetoxy, Me3SiO, Me3Si, PhS, PhSMe+, PhSO, PhSO2, bromo and trimethyls tannyl. The 1J couplings with the olefinic proton span the range 124.3 -193.7 Hz. Substituent-induced chemical shifts (SCS) of most of the nu clei with respect to the alpha-unsubstituted olefin obey simple additi vity in the alpha,alpha-disubstituted compounds and are very similar t o the SCS values along the C-N double bond in the isoelectronic (1,1,3 ,3-tetramethyl-2-indanylidene)amines within the error limits. The exce ptions concern nuclei in the immediate vicinity of the perturbing subs tituent. A dominant mechanistic contribution of electric field effects appears likely for the more distant aromatic part of the indanylidene moiety. The chemical shifts of two (2,2,5,5-tetramethylcyclopentylide ne)methanes are shown to be compatible with the SCS parameters from th e indanylidene series.