The non ‐ reactivity of the chlorine atom in vinyl chloride can be explained

from the molecular orbital point of view as follows. If the chlorine atom has hybridisation, the bond will be a ‐bond and the two lone pairs ofelectrons would occupy the other two orbitals. This would leave a orbital containing a lone pair, and this orbital could now conjugate with the ‐bond of the ethylenic link. Thus two M.O’s will be required to accommodate these four ‐electrons. Furthermore, since chlorine ismore electronegative than carbon, the electrons will tend to be found in the vicinity of the chlorine atom. Nevertheless, the chlorine atomhas now lost full control of the lone pair and so, is less negative than it would have been had there been no conjugation. Since two carbon atoms have acquired a share in the lone pair, each carbon atom acquires a small negative charge. Hence, owing to delocalisation of bonds (through conjugation), the vinyl chloride molecule has an increased stability Before the chlorine atom can be displaced by some other group, the lone pair must be localised again on the chlorine atom. This requires energy, and so the chlorine is more firmly bound.