Whenever the withdrawing electron group (such as halogen) is attached to the end of a carbon chain, a permanent effect called inductive effect takes place. To understand this, consider a chain of carbon atoms having Cl atom at one end: C-C-C-C-ClSince chlorine (Cl) is more electronegative than C, the electron pair shared between C, and Cl is displaced towards the Cl atom, due its larger electronegativity. A partial negative charge (d-) is thus acquired by Cl and C acquires a partial positive charge (d+). The displacement is, not limited to C1-Cl bond but is transmitted to other carbons along the chain. This happens due to the small positive charge on C, which attracts the of electrons of C1-C2 bond towards it. This displacement results in the positive charge on C1 being partially neutralized while a small positive charge is developed on C2. The charge on C2 is less than that on C1 (d'+ < d+).
Similarly, C3 will acquire a small positive charge d +"<d+" < d+').