A correlation has been developed between the structure of adsorbed reaction intermediates and their hydrogenolysis reactivity for aniline in hydrogen pressures up to 0.001 Torr on the Pt(111) surface The composition and orientation of the species involved in aniline hydrogenolysis were characterized using temperature programmed reaction (TPR) and near edge x-ray absorption fine structure (NEXAFS) measurements. The benzene and ammonia formed by aniline hydrogenolysis during TPR on the Pt(111) surface increase substantially in the presence of hydrogen atmospheres. At reaction temperatures, the aromatic ring in aniline remains parallel to the surface in the presence of coadsorbed hydrogen, while in the absence of hydrogen the aromatic ring is tilted relative to the surface. This correlation between orientation and reactivity suggests that a parallel configuration may facilitate hydrogenolysis of the C-N bond in aniline. These in situ studies provide new insight into the structure of surface intermediates which may play a critical role in the mechanisms of aniline hydrogenolysis on the Pt(111) surface in 0.001 Torr of hydrogen.