What evidence is there in The Catcher in the Rye that Holden is disconnected/isolated?
A great example that you could use to suggest that Holden Caulfield is an individual who is profoundly disconnected and isolated from those around him comes at the end of Chapter Seven, when he decides to leave his school early before he is thrown out and to go and stay in a hotel to get his head together before facing his parents. As he packs, he reflects on some ice skates that his mother gave him as a present:
That depressed me. I could see my mother going in Spaulding's and asking the salesman a million dopy questions--and here I was getting the ax again. It made me feel pretty sad... Almost every time somebody gives me a present, it ends up making me sad.
Holden's inability to receive gifts and to accept the love that others have for him and offer to him indicates the extent to which he is disconnected, in every sense, from those around him. It is not enough for him to distance himself physically, but he must also distance himself emotionally, and this is something that is demonstrated in his inability to accept gifts with joy. You also might like to consider the various people that he meets and the way that he tries to form relationships with them but fails.