Chiral và bằng chứng carbonyl
Đã giới thiệu| English | Ý nghĩa |
|---|---|
| enantiomers/eˈnæntɪəməz/ | cặp đồng phân đối |
| chiral centre/ˈkaɪrəl ˈsentə/ | tâm bất đối xứng |
| carbonyl/ˈkɑːbənaɪl/ | nhóm cacbonil |
| racemate | hỗn hợp racemic |
What does zero rotation mean?
- An equal mixture of two enantiomers 对映异构体 has no net optical rotation. An achiral substance also has no rotation.
- Use structure as well as optical evidence before deciding which explanation fits.
Quay quang học bằng chứng minh rằng mẫu là hỗn hợp racemic.
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Một chất achiral là một giải thích khác, do đó cần cấu trúc hoặc bằng chứng phân tách bổ sung.
Identify a chiral centre 手性中心
- A tetrahedral carbon with four different groups is chiral in these examples. Butan-2-ol has H, OH, CH₃ and CH₂CH₃ at carbon 2.
- Propan-2-ol has two identical methyl groups and is achiral. A flat formula cannot determine the measured sign of optical rotation.
Cái nào có carbon chiral?
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Butan-2-ol có bốn nhóm khác nhau tại carbon 2; các carbon trung tâm đề xuất khác thì không.
Combine carbonyl 羰基 tests
- Both aldehydes and ketones give a 2,4-DNPH precipitate. An aldehyde also gives Tollens’ silver or warm Fehling’s brick-red precipitate.
- A ketone usually resists those reducing tests. LiAlH₄ in dry ether gives a secondary alcohol from a ketone after appropriate work-up.
C₃H₆O with two carbon-13 signals, positive iodoform and no Tollens’ silver fits propanone: two equivalent methyl carbons and one carbonyl environment.
Khử LiAlH₄ propanon tạo ra propan-2-_____.
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Phản ứng khử chuyển C=O thành nhóm ancol bậc hai.
Follow cyanide electron pairs
- CN⁻ attacks the carbonyl carbon through its carbon lone pair, while the C=O π pair moves onto oxygen.
- The O⁻ intermediate takes H⁺ from HCN, regenerating CN⁻. Ethanal gives CH₃CH(OH)CN; either carbonyl face is accessible under achiral conditions.
Hai phát biểu nào mô tả phản ứng cộng CN⁻?
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Nucleophile cho cặp electron. Trung gian oxy sau đó nhận proton để tạo hydroxynitrile.
Check whether the product is chiral
- Ethanal addition makes a carbon attached to OH, H, CH₃ and CN, producing a racemate 外消旋体 in the ideal achiral model.
- Propanone addition gives two identical methyl groups at that carbon and no chiral centre. The iodoform test identifies a compatible structural feature, not one unique compound.
“Every carbonyl addition product is chiral” is false. Count the four groups on the new tetrahedral carbon.
Use complete test observations, atom connectivity and three-dimensional groups as independent constraints.
Tại sao sản phẩm cộng hợp propanone–HCN lại không có tính đối xứng quay?
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Hai nhóm giống nhau ngăn chặn carbon đó trở thành tâm bất đối.