Orotic acid is a good organic .building block in coordination chemistry. Its ketonic and enolic tautomers, along with its asymmetric geometry, make it a versatile multidentate organic ligand. Some structures of the orotic acid were optimized with Gaussian98 program package at B3LYP/6 -311 ＋ G ＊ level to fully understand its spatial configurations, isomerization processes, and to obtain some useful parameters. Our calculations show that the steric effect, hydrogen bonding and conjugative effect play an important role in keeping certain configurations, and 1 a is the most stable one in energy. The investigation on the proton-trans- fer processes shows that the energy barriers of proton transfer processes are relatively high, but the energy barriers of the cis-trans isomerization of hydrogen atoms are relatively low. The IR spectra can help us identify different isomers and the vibrational modes in spectrum experiments.%乳清酸是配位化学中的优良配体．它的酮式和烯醇式互变异构体，以及其不对称结构，使其成为多用途的多齿有机配体．在B3LYP／6—311＋G＊高基组水平上，使用Gaussioan 98程序包对乳清酸的结构进行了全优化，以充分理解它的空间构型、异构化过程并获得一些有用参数．研究表明，空间位阻效应、氢键和共轭效应在维持乳清酸空间构型中发挥重要作用，并且异构体1a在能量上最稳定．对异构化过程的研究显示，质子转移过程的能垒相对较高，但顺反异构过程的能垒相对较低．IR光谱能够帮助我们区分不同的异构体和光谱实验中不同的振动模式．
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