Which one of these is not like the others?

Not likely to be seen on Sesame Street, this illustration-in-progress describes a tortured enantiomer named Danny who thinks he's finally found his niche with the Asymmetric Dancing Team. As the poem "Enantiomer in the Mirror" by Mala Radhakrishnan explains:

"Danny was absolutely excited,

For never he’d similar molecules sighted.

So now he could not keep his eagerness in.

“I’m finally going to really fit in!”

But then, as the dancers composed a straight line,

The massive formation was no longer fine.

“Hey Danny, what’s wrong with your orientation?

This line must be perfect with no deviation!”

So Danny then flipped all around and turned,

But soon, he became extremely concerned.

Although he’d the very same groups attached,

The others’ appearance he just couldn’t match."