Can I say, "He needs to go there and not need to participate"?

Solution 1:

Refer to the quotes for quick answers (but I believe your question revolves more around fragments/setting a condition.)

1. Your first sentence can be simply fixed by omitting "to" from "not to"

   He needs to go there and not participate.

2. Your second sentence gives off a different nuance altogether by specifying conditional act i.e. he needs to do A, and/but not B. He has a choice. "Need" implies obligation but more often it serves as a strong suggestion. Compare with "has" for a better feel:

   He needs (or has) to go there but does not need (or have) to participate.

Solution 2:

Taken at face value, the sentences mean somewhat different things. The first sentence—

He needs to go there and not to participate.

—identifies two things that the subject of the sentence needs to do: (1) go there; (2) not participate.

In contrast, the second sentence—

He needs to go there and does not need to participate.

—identifies one thing that the subject of the sentence needs to do (go there) and one thing that he can either do or not do (participate), as he sees fit. The second item is optional because the sentence (1) says that he does not have to participate, and yet (2) does not say that he should not participate.

A somewhat clearer way to express the double requirement in the first sentence is to say this:

He needs to go there, but he also needs to refrain from participating.

And the second sentence might be made slightly clearer by saying this:

He needs to go there, but he does not need to participate.