In chemistry, regioselectivity is the preference of one direction of chemical bond making or breaking over all other possible directions. Although it has been extensively investigated in various reactions, the regioselectivity of hyperconjugative aromaticity on either main group systems or transition metal ones remains elusive due to the challenge of synthesizing the target products. Here we report a joint theoretical and experimental study on this issue.
Molecular nitrogen (N2) is abundant in the atmosphere and nitrogen, found in many biomolecules, is an essential element of life. The Haber–Bosch process, developed over 100 years ago, requires relatively harsh conditions to activate N2 on the iron surface and generate ammonia for use as fertilizer or to produce other chemicals, leading to consumption of more than 2% of the world’s annual energy supply. Thus, developing approaches for N2 activation under mild conditions is particularly important and urgent.
Hyperconjugation and aromaticity are two of the most important concepts in chemistry. Mulliken and co‐workers combined both terms to explain the stability of cyclopentadiene. Here, we carried out DFT calculations on a series of mono‐ and disubstituted cyclopentadiene derivatives to investigate their hyperconjugative aromaticity. Our results revealed that one electropositive substituent can induce aromaticity, whereas one electronegative substituent prompts nonaromaticity rather than antiaromaticity.