Base & Nucleophile Properties
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Are amines bronsted -lowry bases or acids? Effect?
Bronsted-lowry bases Proton acceptors
What effects the strength of amines as a base
The more readily the N: accepts the lone pair = stronger base
Do amines tend to be weak or strong bases?
Weak
List bases in strength order (ammonia, primary aliphatic amines, primary aromatic amines)
Primary aromatic amines < ammonia < Primary aliphatic amines
Why are primary aromatic amines weak in base strength?
Benzene rings withdraw electron density from nitrogen through partial delocalisation - creating a negative conductive effect. N: less readily accepts H+
Why does ammonia have moderate base strength?
N: is available to accept a H+ ion
Why are primary aliphatic have strong base strength?
Alkyl groups donate electrons, increasing electron density on the H - creating a positive inductive effect. N: is more available to accept H+
Why are primary < secondary < tertiary better as nucleophiles?
More alkyl groups so greater inductive effect so N: more readily accepts a H+
Halogenoalkane + ammonia product if the conditions are: 1) Excess ammonia 2) Halogenoalkane
1) Primary amine 2) Secondary, tertiary or quaterary akyl-ammonium ion
Uses of quaternary ammonium salts
Cationic surfacants: Fabric softeners Hair conditioners Detergents
How does quarternary ammonium salts allow non-polar substances to mix with water?
Hydrophobic tail interacts with grease. Hydrophilic tail interacts with water.
E: C6H6NH2 F: C6H6CH2CH2NH2 G: C6H6NHCH2CH3 Explain the difference in base strength of the three amines and give the order of increasing base strength. [6]
[1] (Strength depends on availability of) lone pair on N (atom) [2] E N (next to ring): (lp) delocalised into ring [3] (lp) less available (to donate to or to accept a H+) [4] F or G: N (next to alkyl): (positive) inductive effect/electrons pushed to N [5] (lp) more available (to donate to or to accept a H+) [6] order of increasing base strength E<G<F