Could you please tell me the literal and metaphorical meanings of "Gatsby's head for one link" in this excerpt of The Great Gatsby, Chapter 3?
I wondered if the fact that he was not drinking helped to set him off from his guests, for it seemed to me that he grew more correct as the fraternal hilarity increased. When the “Jazz History of the World” was over girls were putting their heads on men’s shoulders in a puppyish, convivial way, girls were swooning backward playfully into men’s arms, even into groups knowing that some one would arrest their falls—but no one swooned backward on Gatsby and no French bob touched Gatsby’s shoulder and no singing quartets were formed with Gatsby’s head for one link.
Literally, Gatsby is depicted here as being set apart from the crowd at his parties. He is not like his party guests. He does not drink or engage in revelry. When the band stops playing and small groups might be formed to sing songs, standing close with arms around one another's shoulders and waists, Gatsby is not included. He does not spontaneously come together with the others.
The celebrations, the flippant and drunken joy of the parties is simply not for Gatsby and he is not for it. In the literal chain of singers in a quartet, Gatsby will not be one of their number.
In this example, the literal and metaphorical meanings are quite closely related.
To extend the meaning of the phrase "no singing quartets were formed with Gatsby’s head for one link" into a greater metaphorical significance, we can look at how this scene comments on Gatsby's character and his history.
Seen as a "big picture" commentary, we might take this line to relate to the idea that Gatsby has come unmoored from his personal history. Having changed his name, left his parents, and re-made himself, Gatsby is no longer linked to his past. He is not linked to anyone from that past but seeks to be reconnected with one person from it - Daisy.
Until he connects with her in the "link" of marriage that he has envisioned, Gatsby will remain set apart, no matter how large the party.
The fact that Gatsby is out of place at his own parties helps also to suggest that he is a poseur and a performer (of his own persona).