Negative hyperconjugation is donation from an occupied lone-pair or related orbital into an antibonding sigma orbital. Nitrogen-to-P–X sigma-star donation contributes to phosphazene bonding. Short P–N bonds therefore do not require a model dominated by phosphorus pi orbitals.
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Negative hyperconjugation refers to a phenomenon in organic chemistry where electron donation occurs from a filled p orbital or lone pair on a substituent to a π* (pi anti-bonding) orbital of a neighboring bond, such as a carbon-carbon double bond or a carbon-heteroatom bond. This process leads to a stabilization of the system by delocalizing the electrons across the molecule.