Regioselectivity of the intramolecular nucleophilic attack in [RCH−NCHC6H4Y]: A mass spectrometric and computational study

• Regioselectivity of intramolecular nucleophilic attack in [RCH−NCHC6H4Y] was studied.
• NO2 favors C3-attack to form spiro-σ-adduct and it also contributes to the loss of HCN.
• Other substituents (H, OMe, NMe2 and Cl) favor C4-attack to yield bicyclo-σ-adduct.
• It is difficult for bicyclo-σ-adduct to lose HCN.
• DFT calculations are well consistent with the tandem mass spectrometry experiments.

The investigation into the intramolecular nucleophilic attack in carbanion [RCH −NCHC6H4Y] in the gas phase has been carried out by mass spectrometry and density functional theory (DFT). The main results of the present work are as follows: the regioselectivity of the intramolecular attack depends on the substituent on the para-position of the benzene ring. NO2 favors C3-attack to form spiro-σ-adduct and it also contributes to the loss of HCN, while other substituents (H, OMe, NMe2 and Cl) favor C4-attack to yield bicyclo-σ-adduct and in this condition, HCN cannot be lost. In the meantime, DFT calculations also demonstrate that the loss of HCN from the spiro-σ-adduct is both thermodynamically and kinetically beneficial, while that from the bicyclo-σ-adduct is disadvantageous either in kinetics or thermodynamics.

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