Explain the movement of electrons in organic reactions.

(N/A) The movement of electrons in organic reactions is represented using curved-arrow notation. This notation illustrates how bonding changes occur due to electronic redistribution during a reaction.
$1$. To show the shift of an electron pair,a curved arrow starts from the source (where the electron pair is located) and ends at the destination (where the pair moves).
$2$. To show the movement of a single electron,a single-barbed 'fish-hook' (half-headed curved arrow) is used.
Examples of electron movement:
$(i)$ Nucleophilic attack: $HO^{-} + CH_3 - Br \rightarrow CH_3OH + Br^{-}$
$(ii)$ Homolytic fission: $H_3C - Cl \rightarrow \cdot CH_3 + \cdot Cl$ (one electron moves to $C$ and one to $Cl$ from the shared bond pair).
Common patterns of electron movement are shown below:
$(i)$ From $\pi$ bond to adjacent bond position.
$(ii)$ From $\pi$ bond to adjacent atom.
$(iii)$ From an atom with a lone pair to an adjacent bond position (forming a $\pi$ bond).