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While studying the electrophilic cyclization of acetylenic malonates in synthesizing malonate indene derivatives with high regio and stereo-selectivity, we found that the CH2 and CH3 protons of two COOCH2CH3 groups in some diethyl malonate indene derivatives showed very interesting spin-spin coupling and signal multiplicity. To explain those phenomena, we synthesized several diethyl malonate indene derivatives, and then used 1H NMR spectra and molecular modeling to investigate the CH2CH3 spin system of these two COOCH2CH3 groups in detail. The results showed that the spin systems of CH3CH2 of the two COOCH2CH3 groups in those compounds may exist in different froms (AMX3, ABX3 and A2X3), and the effect of the aromatic ring induced by the phenyl group at the end of the triple bond is the main reason responsible for those phenomena.
While studying the electrophilic cyclization of acetylenic malonates in synthesizing malonate indene derivatives with high regio and stereo-selectivity, we found that the CH2 and CH3 protons of two COOCH2CH3 groups in some diethyl malonate indene derivatives showed interesting spin-spin coupling and signal multiplicity. To explain those phenomena, we had several diethyl malonate indene derivatives, and then used 1H NMR spectra and molecular modeling to investigate the CH2CH3 spin system of these two COOCH2CH3 groups in detail. The results showed that the spin systems of CH3CH2 of the two COOCH2CH3 groups in these compounds may exist in different froms (AMX3, ABX3 and A2X3), and the effect of the aromatic ring induced by the phenyl group at the end of the triple bond is the main reason responsible for those phenomena.