an organic compound usually formed as an intermediate product in the preparation of acetals from aldehydes or ketones
例句
The thiophane ring was established via reduction of hemiacetal, mesylation of diol, and double SN2 substitution of dimesylate. 经半缩醛的还原，甲磺酸酯化，硫代关环，构建四氢噻吩环；
The thiophane ring was established via reduction of hemiacetal, tosylation of diol, and double SN2 substitution of ditosylate. 第二章设计了以从棕榈籽制备的D-甘露糖为手性源，经聚苯乙烯负载三氯化铁催化异亚丙基化、苯甲酰基保护、选择性水解、聚苯乙烯负载二乙酸碘苯氧化、Wittig-Horner反应引入侧链、催化氢化、一锅法脱苯甲酰基及半缩醛还原、对甲苯磺酸酯化、硫代关环、构建四氢噻吩环；
With the absence of oxygen, branched alkaline would be produced.Whereas when oxygen was available, some other structures like hemiacetal, ether bond were produced. 其中无氧条件下可能发生侧链烷烃交联而形成支链，在有氧分子参与的情况下，反应进一步进行形成一些架桥结合，诸如半缩醛、醚键等等。
And finally we found that undering the catalysis of L-proline, the anhydride materials which are easily ringing formed hemiacetal cannot react with acetone using asymmetric Aldo reaction. 并发现，在L-脯氨酸催化下，易形成环状半缩醛结构的醛类化合物与丙酮不能进行不对称羟醛缩合反应。
any monosaccharide sugar that contains a ketone group or its hemiacetal. 任何一种含有酮基或其半缩醛的单糖。
a monosaccharide sugar that contains the aldehyde group or is hemiacetal. 含有乙醛基或其半缩醛的单糖。
