Learning Objective: To study the nucleophiles that function as sigma bond donors that form Carbon, Hydrogen, and Halogen bonds with the substrate.
Prerequisites:
Electronegativity trend of the elements from the Periodic table
Group 13 elements
Chapter: Fundamentals of Organic Reactions
Sub-topic: Nucleophiles
Author's Note: The use of metals is prevalent in organic chemistry. The electropositive nature of metals compels carbon to form carbanions (R-) and hydrogen to form hydrides (H-) in reactions. This reversal in their polarity in the presence of metals boosts reactions, builds carbon chains, and introduces structural variety. This section will teach you which types of metals are good sigma bond donors and what structural change gets introduced in the product.
Type of Nucleophile - Sigma Bond
The atoms like Lithium (Li) and Magnesium (Mg) on the left side of the periodic table are electropositive, meaning they are happier to donate their electrons and become positively charged species. For example, Li and Na can donate one electron, Be and Mg can donate two electrons to form Li+ and Mg2+ species.

By donating their electrons, these metals can convert a starting material RX (an alkyl halide) into a reactive .....
The bond of metal with carbon is highly polar, and the most electron density resides with the electronegative carbon....
Still, unlike the electronegative atoms on the periodic table's right side, they don't prefer to keep it to themselves. These elements cannot hold the sigma bond electrons very efficiently ....