More Electropositive is More Electronegative: Atom Size Determines C=X Group Electronegativity.

Area of Science:

• Quantum Chemistry
• Periodic Trends
• Chemical Bonding

Background:

• The electronegativity of the C=X group is typically assumed to decrease as the electronegativity of X decreases.
• Periodic trends in atomic size and electronegativity influence chemical properties.

Purpose of the Study:

• To investigate the counterintuitive trend of C=X group electronegativity down groups 16, 15, and 14.
• To elucidate the role of atomic size in determining C=X group electronegativity.
• To explore applications in tuning hydrogen-bond donor strength.

Main Methods:

• Quantum-chemical analyses were employed.
• Systematic examination of the C=X group across different periodic table groups.

Main Results:

• The C=X group becomes effectively more electronegative as atom X decreases in Pauling electronegativity down a group.
• This phenomenon is directly linked to the increasing atomic size of X.
• Amides with larger X atoms (e.g., silicon) exhibit stronger hydrogen-bond donating capabilities.

Conclusions:

• Atomic size, not just electronegativity, is a critical factor in determining the electronic properties of the C=X group.
• These findings offer a new perspective on tuning hydrogen-bond donor strength in amides.
• The study provides a basis for designing molecules with tailored hydrogen-bonding properties.