Nitrogen lone pairs, charge and polymer links
Introduced| English | Meaning |
|---|---|
| amine/ˈæmaɪn/ | An organic compound derived from ammonia by replacing one or more hydrogen atoms with carbon-containing groups. |
| zwitterion/zwɪˈtɪərɪən/ | A particle with both positive and negative charges on different parts, but no overall charge. |
| polyamide/ˌpɒlɪˈeɪmaɪd/ | A polymer whose chain contains repeating amide links. |
| hydrogen bonds/ˈhaɪdrədʒn bɒndz/ | An attraction between a hydrogen atom bonded to an electronegative atom and a suitable electronegative atom with a lone pair. |
Follow the nitrogen lone pair
- An amine 胺 accepts H⁺ through its nitrogen lone pair. Alkyl groups generally increase electron density and basicity relative to ammonia.
- In phenylamine, interaction with the ring makes the lone pair less available. Its basicity is lower.
Keep the nitrile carbon
- Reducing propanenitrile with LiAlH₄ in dry ether then work-up gives propan-1-amine. The nitrile carbon remains in the chain.
- Nitrobenzene instead needs Sn/HCl to make phenylammonium salt; alkali then releases phenylamine.
How many carbon atoms remain when propanenitrile is reduced to an amine?
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All three carbons, including the nitrile carbon, remain.
Track both amino-acid groups
- A zwitterion 两性离子 has NH₃⁺ and COO⁻ groups and zero net charge. In strong acid, COO⁻ becomes COOH.
- In strong alkali, NH₃⁺ becomes NH₂ while COO⁻ remains. Glycine is achiral because its central carbon has two H atoms.
Glycine’s alkaline form is H₂NCH₂COO⁻, with net charge −1, not the zero-charge zwitterion.
Which is glycine’s principal form in strong alkali?
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Alkali removes the ammonium proton while the carboxyl group remains deprotonated.
Glycine is achiral because the central carbon has two identical _____ atoms.
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Two identical hydrogen substituents prevent a four-different-group chiral centre.
Locate the polymer backbone
- A polyamide 聚酰胺 has –C(=O)–NH– links in its backbone. Condensation produces those links and a small molecule.
- Poly(propenamide) instead opens C=C by addition. Its amide side groups do not make the reaction condensation.
Every polymer with an amide side group is formed by condensation.
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Poly(propenamide) is an addition polymer with amide side groups.
Explain properties through interactions
- Polyamide N–H and C=O groups form hydrogen bonds 氢键 between chains. These help hold fibres together.
- Poly(ethenol) OH groups hydrogen-bond to water, supporting suitable water-soluble laundry-bag applications.
The presence of an amide group alone does not classify the polymerisation route.
Locate the nitrogen lone pair and its availability before comparing bases. Read the actual reacting groups and links to distinguish addition from condensation polymerisation.
Which two groups form hydrogen bonds between polyamide chains?
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N–H can donate and carbonyl oxygen can accept hydrogen bonds.