  The chemical composition of the inner region of protoplanetary disks can
trace the composition of planetary building material. The exact elemental
composition of the inner disk has not yet been measured and tensions between
models and observations still exist. Recent advancements have shown
UV-shielding to be able to increase emission of organics. Here, we expand on
these models and investigate how UV-shielding may impact chemical composition
in the inner 5 au. In this work, we use the model from arxiv:2204.07108 and
expand it with a larger chemical network. We focus on the chemical abundances
in the upper disk atmosphere where the effects of water UV-shielding are most
prominent and molecular lines originate. We find rich carbon and nitrogen
chemistry with enhanced abundances of C2H2, CH4, HCN, CH3CN, and NH3 by > 3
orders of magnitude. This is caused by the self-shielding of H2O, which locks
oxygen in water. This subsequently results in a suppression of
oxygen-containing species like CO and CO2. The increase in C2H2 seen in the
model with the inclusion of water UV-shielding allows us to explain the
observed C2H2 abundance without resorting to elevated C/O ratios as water
UV-shielding induced an effectively oxygen-poor environment in oxygen-rich gas.
Thus, water UV-shielding is important for reproducing the observed abundances
of hydrocarbons and nitriles. From our model result, species like CH4, NH3, and
NO are expected to be observable with the James Webb Space Telescope (JWST).
