Stereoisomerism
| English | Chinese | Pinyin |
|---|---|---|
| stereoisomerism | 立体异构 | lì tǐ yì gòu |
| geometrical | 几何 | jǐ hé |
| restricted rotation | 受限旋转 | shòu xiàn xuán zhuǎn |
| optical isomerism | 旋光异构 | xuán guāng yì gòu |
| chiral centre | 手性中心 | shǒu xìng zhōng xīn |
| enantiomer | 对映体 | duì yìng tǐ |
Mirror images and rigid bonds
- In stereoisomerism 立体异构 the atoms are joined in the same order but point in different directions in space.
- Two kinds: geometrical 几何 and optical.
- Both matter a lot in real molecules.
Stereoisomerism lab
Sort stereoisomer examples by the 3D feature that creates them.
In stereoisomerism, the atoms are:
Stereoisomers share the same connectivity but differ in 3-D arrangement.
E/Z (cis-trans) isomerism arises because there is no rotation about a C=C double bond.
The restricted rotation fixes the groups' positions.
Geometrical (cis/trans)
- Happens at a C=C double bond.
- The pi bond stops the carbons rotating (restricted rotation 受限旋转), so groups are fixed:
- cis = on the same side; trans = on opposite sides.
A nucleophile attacks an electron-poor centre; an electrophile is drawn to an electron-rich one
Geometrical (cis/trans) isomerism happens at a C=C bond because:
Restricted rotation about the C=C bond fixes groups cis (same side) or trans (opposite sides).
Match each stereochemistry term.
Each item links the term to its correct meaning.
Optical isomerism 旋光异构
- Happens at a chiral centre 手性中心 — a carbon with four different groups.
- It gives two mirror-image forms, enantiomers 对映体, that cannot be superimposed.
- A molecule can have more than one chiral centre.
A chiral centre is a carbon with:
A carbon bonded to four different groups is chiral and gives two mirror-image forms.
Enantiomers are:
Optical isomers (enantiomers) are mirror images that cannot be superimposed on each other.
When does E/Z isomerism occur?
- It needs a C=C double bond with two different groups on each carbon.
- If either carbon carries two identical groups, there is no E/Z isomerism.
You've got it
- stereoisomers = same order of atoms, different directions in space
- geometrical (cis/trans): at a C=C bond, restricted rotation fixes groups on the same (cis) or opposite (trans) sides
- optical: at a chiral centre (carbon with 4 different groups) → non-superimposable mirror images (enantiomers)