3.11 Amines
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Draw the structures of primary, secondary and tertiary amines and a quaternary ammonium ion
How do you name amines?
-amine or amino-
Why are amines so reactive?
The lone pair of electrons on the nitrogen- due to polar N-H bond
What shape are amines around the N? Bond angle?
Trigonal pyramidal, 107 degree due to lone pair on N
What kind of intermolecular forces do they have? Why?
Hydrogen bonding due to polar N-H bond and lone pair of electrons on N atom
Do amines have intermolecular forces which are stronger than or weaker than alcohols? Why?
Weaker, as N has a lower electronegativity than O —> weaker hydrogen bonding
What state are amines at 298K?
Short chains are gases, longer chains are volatile liquids
What do they smell of? Why?
Fishy smell - rotting fish/flesh releases di- and triamines
Which primary amines are soluble in water/alcohols? Why?
Up to 4 carbon atoms, as they can hydrogen bond to water molecules. After this, non-polarity of hydrocarbon chain makes them insoluble
What kind of solvents are most other amines soluble in?
Less or non-polar solvents
Solubility of phenylamine? Why?
Not very soluble, due to the non-polarity of the benzene ring - C6H5 cannot form hydrogen bonds
How can/when do amines act as bases?
When they bond with a H+ ion
How can/ when do amines act as nucleophiles?
When they bond with an electron deficient C atom (donate lone pair from N)
Draw a mechanism for the basic action of an amine with water
Slide 30
What is the product from the basic action of an amine with water?
RNH3 + - ammonium ion, which forms a salt with an anion
Is the product (ammonium ion) soluble in water? Why?
Yes, as it is ionic so is attracted to the polar bonds in H2O
How could you regenerate the soluble amine from the ammonium salt?
Add a strong base (NaOH) —> removes H+ ions from ammonium ion
In order to be the strongest base, what must a particular amine have (out of a set of amines)?
Greatest electron density around the N atom, making it a better electron pair donor (attracts protons more)
What does positive/negative inductive effect mean?
Positive inductive effect = donate electrons, increase density around N Negative means remove electrons, decrease density around N
What effect do alkyl groups have (on electron density and base strength)
Positive inductive effect - increase electron density around N —> stronger base
What effect do aryl groups have (on electron density and base strength)?
Negative inductive effect - decrease electron density around N —> weaker base
Why are 3^0 amines never good bases
They are insoluble in water
Place these in order of base strength (in general): NH3, 1^0 amine, 2 ^0 amine, phenylamine
2 ^0 amine > 1 ^0 amine > NH3 > phenylamine
Draw a mechanism for the nucleophilic substitution of NH3 with RCH2Br to form primary amines
Slide 50