Primary and secondary amines
Introduced| English | Meaning |
|---|---|
| amine/ˈæmaɪn/ | An organic compound derived from ammonia by replacing one or more hydrogen atoms with carbon-containing groups. |
| amino acid/əˈmiːnəʊ ˈæsɪd/ | An organic molecule containing amino and carboxyl groups; these molecules join to form proteins. |
| lone pair/ləʊn peə/ | A pair of outer-shell electrons on one atom that is not shared in a covalent bond. |
| basicity/beɪˈsɪsɪti/ | The tendency of a substance to behave as a base, such as by accepting a proton. |
| phenylamine/ˌfiːˈnaɪləmiːn/ | An aromatic amine with an NH2 group directly attached to a benzene ring. |
Nitrogen-based bases
- Amines 胺 are everywhere — in amino acids 氨基酸, proteins, medicines and dyes.
- An amine has an –NH₂ group (primary) or –NH– (secondary).
- The nitrogen keeps a lone pair 孤对电子, and that lone pair is what makes amines bases.
Amine type lab
Classify amines by substitution at nitrogen and basic behaviour.
A primary amine has the group:
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A primary amine has –NH₂; a secondary amine has –NH– between two carbons.
Amines act as bases because the nitrogen has a lone ______.
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It accepts a proton.
Making amines
- a halogenoalkane + NH₃ (in ethanol, under pressure) → a primary amine.
- that primary amine + more halogenoalkane → a secondary, then tertiary amine.
- reduction of an amide or nitrile with $\text{LiAlH}_4$ → an amine.
- (and an amine or ammonia + an acyl chloride → an amide.)
Amine basicity 碱性 depends on the availability of the nitrogen lone pair
A primary amine is made by heating a halogenoalkane with:
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Ammonia substitutes the halogen to give the amine (excess NH₃ favours the primary amine).
Reducing a nitrile or amide with LiAlH₄ gives:
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LiAlH₄ reduces both nitriles and amides to amines.
Match each term to its meaning.
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Each item links the term to its correct meaning.
Why amines are bases
- The nitrogen lone pair accepts an $\text{H}^+$ — so an amine is a base (a proton acceptor).
- The more available that lone pair, the stronger the base.
- Alkyl groups push electrons onto N, making the pair more available; a benzene ring pulls it away.
Basicity order: ethylamine > ammonia > phenylamine 苯胺.
- Ethylamine (CH₃CH₂NH₂): the ethyl group donates electrons, so the lone pair is more available — the strongest base here.
- Ammonia (NH₃): no help, no hindrance — the baseline.
- Phenylamine (C₆H₅NH₂): the lone pair is drawn into the benzene ring, so it is least available — the weakest base.
A primary amine has-NH2; a secondary amine has-NH-
Amines are bases because:
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The nitrogen lone pair accepts H⁺, making the amine a base.
Primary, secondary, tertiary
- Amines are classed by how many carbon groups are attached to the nitrogen.
- 1° = one (e.g. CH₃NH₂); 2° = two (e.g. (CH₃)₂NH); 3° = three (e.g. (CH₃)₃N).
- All act as bases, because the nitrogen still keeps its lone pair in each case.
Two routes to an amine: from a halogenoalkane, or by reducing a nitrile
You've got it
- amine = –NH₂ (1°), –NH– (2°), or three carbons on N (3°)
- made from halogenoalkane + NH₃, or by reducing a nitrile/amide ($\text{LiAlH}_4$)
- amines are bases — the nitrogen lone pair accepts $\text{H}^+$
- basicity: ethylamine > ammonia > phenylamine (alkyl donates to N; a ring pulls the pair away)