用一个对称性的分子进行不对称合成时,必须有一个物理的或化学的不对称因素存在。常用的化学不对称因素,有不对称催化剂、不对称试剂等。如还原丙酮酸时,氢原子从两个相反的空间方向进攻羰基双键,结果是产生等量的左旋和右旋的产物。如果让丙酮酸先与光活性胺反应生成酰胺后再进行还原,结果会产生不等量的左旋和右旋体。显然,后者,即光活性胺,对第二个不对称中心的产生具有诱导作用。这种作用叫做光活诱导作用(或光活感 Asymmetric synthesis with a symmetric molecule requires the presence of a physical or chemical asymmetry. Common chemical asymmetry factors, asymmetric catalysts, asymmetric reagents. When pyruvate is reduced, the hydrogen atoms attack the carbonyl double bond in two opposite spatial directions, resulting in an equivalent amount of levorotatory and dextrorotatory products. If pyruvate and photoactive amine react with amines and then reduce, the result will produce unequal amounts of levorotary and dextral. Obviously, the latter, the photoactive amine, has an inducing effect on the second asymmetric center. This effect is called phototropism (or photorealism)