How to increase percent yield? How to improve experiment? Nitration of Veratrole?

Can you provide a bit more detail about the experimental conditions and the precise reaction you were attempting?
As a general rule, most reactions do not result in 100% yield, and so, this might be the limits of the reaction. Alternatively, one of your reagents was limiting, and caused a reduced yield.

The reaction was the synthesis of 4-nitro veratrole. Veratrole was the limiting reagent and it was reacted with acetic acid and nitric acid. The percent yield was calculated using veratrole (because it was the lr) so that wouldn’t be the reason for the reduced yield. Sterics inhibit the intermediate state prevent the production of 3-nitro-veratrole, but i am unsure whether 4,5-dinitro-veratrole would be possible as that would result in a lower yield of 4-nitro-veratrole

What about using an oxymercuration step to inhibit the formation of the di-nitration product. The mercury acetate would form the partial positive carbon intermediate that would allow for faster addition of the NO2.

I don’t know if this is completely valid because I’m not sure if this would be totally selective for 4-nitro-veratrole. There might be some 3-nitro-veratrole, but I feel as though due to sterics the mercury acetate would attack the farthest side from the -OCH3 groups leaving more selectivity towards the 4-nitro product.