Not sure what "hoptree" is. Is it wafer ash (Ptelea trifoliata)? Yours looks like one I found a few yrs ago nearby:

Can't really say what problem yours is having, but that kind of soil showing prb'ly dries out quickly, tho dryness would cause wilting first & usually not yellowing.

Don't have any lawnchairs and couldn't find a suitable screen. Search continues. Meanwhile Disease/Condition X takes its toll. I planted this in the fall, so I don't think it would be scorch? All these leaves were a beautiful green a couple of weeks ago and then bam. That is when we started to get the heat though...

Hmm -- scorch. Wafer ash IS a shade-lover -- the one I show above was in deep shade, but hardly anyone has experience w/them, so difficult to guess. Might put a vertical board or fabric supported by stakes to the west or even overhead to shade from the hot afternoon sun.....

I agree, it much be too much sun since I'm not under or overwatering it, and I just don't think it's nitrogen deficiency. And all the hoptrees I see around here ARE in the woods in part sun. But everywhere I read says full OR part sun, so not sure what to think. It's not like I'm in FL or AL.

i wonder if I should just go ahead and transplant it to a shadier site rather than finding a screen for it. Am I going to screen it its whole life, or do you think full sun is something it will get acclimated to?

Many plants are less sensitive to conditions as they get older w/a better root system. But yours is small enough that transplanting into shadier conditions might be best, tho doing it now could be risky. I'll emphasize getting a BIG rootball & keeping it intact (if there's no clay in the soil, that might be difficult), as this isn't an ideal time to transplant. Or you might shade now & transplant in the fall.

hoptrees are shade-loving. I agree with beng12, it would be best to transplant it into a shadier spot