In the compound CH3-CH2-CN the electrophilic centre according to my NCERT TEXTBOOK(class 11) is the carbon of cyanide but I think it should be the the carbon adjacent to cyanide since, during bond cleavage between cyaninde and ethyl the electron pair will be taken up by the carbon of cyanide so in this way it is a neucleophilic centre . Hence I think that the carbon of ethyl should be electrophilic centre. Am I right or iam missing something or my textbook is wrong? Any help is greatly appreciated.
In all of the compounds illustrated, the starred carbon is connected to a more electronegative element.
Let's examine this one by one- I shall begin with methyl iodide. Here, the starred carbon is connected to a Iodine which is more electronegative, thus naturally, we can guess that the electron density shifts towards the halogen. Thus, the carbon in question is slightly electron deficient (slightly positive or electrophilic)
Now, let's look at the examples with the multiple bonds. Consider ethanal: the carbon is again connected to a more electronegative atom i.e oxygen. So, if you were to cleave the pi bond, the electron density would shift to the oxygen, and again you are left with an electrophilic carbon right next to the oxygen.
The same can be said for the acetonitrile: the electron density shifts to the more electronegative element i.e nitrogen and the carbon right next to is left "slightly positive" or electrophilic.
The electron density would always be slightly greater in the vicinity of a more electronegative element across a bond between two atoms differing in electronegativity (essentially, what we mean when we say a bond is polar)