Definition of a nucleophilicity scale

Area of Science:

• Physical Chemistry
• Computational Chemistry
• Chemical Reactivity

Background:

• Nucleophilicity is a fundamental concept in chemical reactivity.
• Existing empirical scales of nucleophilicity require further validation and theoretical correlation.
• Understanding nucleophile-electrophile interactions is crucial for predicting reaction outcomes.

Purpose of the Study:

• To evaluate experimental nucleophilicity indices proposed by Legon and Millen.
• To correlate theoretical parameters with experimental nucleophilicity scales.
• To propose a new nucleophilicity index for orbital-controlled reactions.

Main Methods:

• Utilized force constants derived from vibrational frequencies of H-X (X=F, CN) probe dipoles.
• Calculated theoretical parameters including electrostatic potential V(min), binding energy (BE), and V(H).
• Evaluated binding energies of nucleophiles with Lewis acids BF(3) (hard) and BH(3) (soft).

Main Results:

• Good correlations were found between experimental nucleophilicity and theoretical parameters (V(min), BE, V(H)).
• The Legon and Millen scale and electrostatic potential scales accurately predict reactivity for hard-hard electrophile interactions.
• A novel nucleophilicity index based on frontier orbitals was proposed for orbital-controlled interactions.

Conclusions:

• Empirical and electrostatic potential-based nucleophilicity scales are effective for hard-hard interactions.
• A new theoretical index is needed to describe orbital-controlled nucleophilic reactions.
• This research provides insights into quantifying and predicting nucleophilic reactivity.