Amines flash cards

1. 1.What are amines and how are they structurally related to ammonia?

   Amines are derivatives of ammonia ($NH_3$) in which one, two, or all three hydrogen atoms are replaced by alkyl or aryl groups. They contain the amino group $-NH_2$, $>NH$, or $-N<$ built around a trivalent nitrogen.

   Hint: Replace H of NH3 with R/Ar

2. 2.How are amines classified as primary, secondary, and tertiary?

   Classification is based on the number of hydrogen atoms of $NH_3$ replaced by alkyl/aryl groups: primary $1^\circ$ ($R-NH_2$, one group), secondary $2^\circ$ ($R_2NH$, two groups), tertiary $3^\circ$ ($R_3N$, three groups).

   Hint: Count groups attached to N

3. 3.On what basis are alcohols and amines each classified — is the criterion the same?

   No. Alcohols/haloalkanes are classified by the nature of the carbon bearing the group. Amines are classified by the number of carbon groups attached directly to nitrogen. So $(CH_3)_3C-NH_2$ (tert-butylamine) is a $1^\circ$ amine even though carbon is tertiary.

   Hint: Amine class = groups on N, not on C

4. 4.Draw the shape and hybridisation of the nitrogen in an amine.

   Nitrogen is $sp^3$ hybridised with a pyramidal shape. Three sigma bonds (to H or C) and one lone pair occupy the four hybrid orbitals, giving a pyramidal geometry similar to $NH_3$.

   Hint: sp3, lone pair, pyramidal

5. 5.Why is the C–N–C (or H–N–C) bond angle in trimethylamine about $108^\circ$ rather than the ideal tetrahedral $109.5^\circ$?

   The lone pair on nitrogen occupies more space and repels the bond pairs, and the bulky methyl groups add strain. This lone pair–bond pair repulsion slightly compresses the angle to about $108^\circ$.

   Hint: Lone pair–bond pair repulsion

6. 6.What is the difference between an aliphatic amine and an aromatic amine?

   In an aliphatic amine the nitrogen is attached only to alkyl groups (e.g. $CH_3NH_2$). In an aromatic amine the nitrogen is attached directly to an aromatic ring (e.g. aniline, $C_6H_5NH_2$). Benzylamine ($C_6H_5CH_2NH_2$) is aliphatic since N is on a $CH_2$, not the ring.

   Hint: N directly on ring = aromatic

7. 7.Give the IUPAC and common name of $CH_3NH_2$.

   IUPAC: methanamine. Common: methylamine. The suffix -e of the alkane is replaced by -amine.

   Hint: methane → methanamine

8. 8.Give the IUPAC name of $CH_3CH_2CH_2NH_2$.

   Propan-1-amine (common: n-propylamine). The chain is numbered so nitrogen gets the lowest locant.

   Hint: Propane → propan-1-amine

9. 9.How is a secondary/tertiary amine with different groups named in IUPAC nomenclature? Give the name of $CH_3-NH-CH_2CH_3$.

   The largest group is the parent; other groups on nitrogen are named as N-substituents. $CH_3-NH-CH_2CH_3$ is N-methylethanamine.

   Hint: Prefix substituents on N with 'N-'

10. 10.Name $(CH_3)_3N$ by IUPAC and common systems.

    IUPAC: N,N-dimethylmethanamine. Common: trimethylamine. Ethanamine is the parent-like largest? Here all three are methyl, so parent = methanamine with two N-methyl substituents.

    Hint: N,N-dimethylmethanamine

11. 11.What is the IUPAC name of aniline?

    Benzenamine (aniline is the accepted common/retained name). It is the parent aromatic amine, $C_6H_5NH_2$.

    Hint: Benzene + amine

12. 12.Name $C_6H_5-NH-CH_3$.

    N-methylbenzenamine, commonly N-methylaniline.

    Hint: Methyl on aniline N

13. 13.Name $C_6H_5-N(CH_3)_2$.

    N,N-dimethylbenzenamine, commonly N,N-dimethylaniline.

    Hint: Two methyls on aniline N

14. 14.What is the common name for $H_2N-CH_2CH_2CH_2CH_2CH_2CH_2-NH_2$ type diamines — specifically $H_2N(CH_2)_6NH_2$?

    Hexane-1,6-diamine (hexamethylenediamine), a diamine used to make nylon-6,6. Two amino groups are named with the -diamine suffix.

    Hint: 1,6-diamine of hexane

15. 15.How are amines generally prepared by reduction of nitro compounds? Give the product from nitrobenzene.

    Nitro compounds are reduced to primary amines. Nitrobenzene $\xrightarrow{H_2/Ni\ or\ Sn+HCl}$ aniline ($C_6H_5NH_2$). Reagents: $H_2/Pd$ or $Fe/HCl$ or $Sn/HCl$.

    Hint: $-NO_2 \rightarrow -NH_2$

16. 16.Why is Fe/HCl often preferred over Sn/HCl for reducing nitrobenzene to aniline industrially?

    $Fe/HCl$ is preferred because $FeCl_2$ formed is hydrolysed to regenerate $HCl$, so only a small amount of $HCl$ is needed, making it cheaper. Both give aniline.

    Hint: HCl regenerated, cheaper

17. 17.How are amines prepared by reduction of nitriles? What class of amine forms?

    Nitriles are reduced by $H_2/Ni$ (or $LiAlH_4$) to primary amines: $R-CN \xrightarrow{H_2/Ni} R-CH_2-NH_2$. This adds one carbon to the chain (step-up).

    Hint: $R-CN \rightarrow R-CH_2NH_2$

18. 18.What amine forms on reduction of $CH_3CN$ with $LiAlH_4$?

    Ethanamine, $CH_3CH_2NH_2$. Reduction of the nitrile $-C\equiv N$ adds two hydrogens across to give the primary amine with one extra carbon than the alkyl group.

    Hint: Acetonitrile → ethylamine

19. 19.How are primary amines prepared by reduction of amides?

    Amides are reduced by $LiAlH_4$ to primary amines: $R-CONH_2 \xrightarrow{LiAlH_4} R-CH_2-NH_2$. Unlike nitrile reduction, carbon count of chain is retained relative to acid carbon.

    Hint: $R-CONH_2 \rightarrow R-CH_2NH_2$

20. 20.Describe the ammonolysis of alkyl halides. Why is it not a clean method?

    An alkyl halide reacts with excess $NH_3$: $R-X + NH_3 \rightarrow R-NH_2 + HX$. It is not clean because the primary amine is itself nucleophilic and reacts further to give $2^\circ$, $3^\circ$ amines and quaternary ammonium salt — a mixture forms.

    Hint: Gives mixture of 1°,2°,3°,4°

21. 21.How can a primary amine be favoured as the major product in ammonolysis of an alkyl halide?

    By using a large excess of ammonia. Excess $NH_3$ minimises further alkylation of the primary amine, so the $1^\circ$ amine predominates.

    Hint: Large excess NH3

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