Understanding the molecular orientation is crucial for revealing the mechanism of chemical reactions. However, how to accurately monitor the molecular orientation remains a great challenge because of the motion of the molecules during the chemical reaction. Here, surface-enhanced Raman spectroscopy (SERS) was used to monitor the molecular reorientation from the plasmon-catalyzed conversion of p-aminothiophenol (PATP) to p,p'-dimercaptoazobenzene (DMAB). Spectral change due to molecular reorientation, which is often overlooked, is clearly extracted through the protonation of the PATP molecules to suppress the conversion of PATP to DMAB. Meanwhile, by monitoring the Raman features, the reaction process and molecular reorientation are simultaneously recorded, offering fresh insights on the long-standing puzzle that why the conversion to DMAB is suppressed with concentrated PATP: this is because the over-crowded PATP adsorbed on the substrate hampered its own space-taking reorientation (similar to the space-steric effect) which is a prerequisite for producing DMAB.

了解分子取向对于揭示化学反应的机制至关重要。然而，由于分子在化学反应过程中的运动，如何准确监测分子取向仍然是一个巨大的挑战。在这里，表面增强拉曼光谱 (SERS) 用于监测从等离子体催化的对氨基苯硫酚 (PATP) 转化为对，对'-二巯基偶氮苯 (DMAB) 的分子重新取向。由于分子重新定向引起的光谱变化（通常被忽视）通过 PATP 分子的质子化明显提取，以抑制 PATP 向 DMAB 的转化。同时，通过监测拉曼特征，同时记录反应过程和分子重新取向，