Quantifying the conceptual problems associated with the isotropic NICS through analyses of its underlying density

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Organic Chemistry

Background:

• The isotropic Nucleus Independent Chemical Shift (NICSiso) is a common metric for assessing aromaticity.
• Existing studies show strong correlations between NICSiso values and other aromaticity descriptors.

Purpose of the Study:

• To investigate the fundamental origins of the correlations observed with NICSiso.
• To establish causal relationships between NICSiso and electronic current density patterns.

Main Methods:

• Decomposition of NICSiso values into their constituent electronic density components.
• Analysis of the relationship between NICSiso and underlying current density distributions.

Main Results:

• The behavior of NICSiso can arise from factors fundamentally different from current assumptions.
• Established correlations with other aromaticity measures may not always reflect the expected electronic origins.

Conclusions:

• The reliability of NICSiso as a universal descriptor for aromaticity is questioned.
• Interpretations of NICSiso values require caution and should be supported by additional data beyond simple correlations.