Let us look at a molecule called Chloroethane (CH3-CH2-Cl). 1. Identify the group: Chlorine (Cl) is much more electronegative than Carbon. 2. The Bond: The bond between Carbon and Chlorine is a sigma bond. 3. The Pull: Chlorine pulls the shared electrons towards itself. This makes Chlorine slightly negative (delta minus, δ-) and the neighboring Carbon slightly positive (delta plus, δ+). 4. The Chain: That first carbon then pulls electrons from the second carbon. This effect gets weaker: Carbon 1 is more positive than Carbon 2. 5. Result: Chlorine shows a -I effect here.