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Lecture31outline - I Review The nitrogen atom in amines is...

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I. Review • The nitrogen atom in amines is effective at accepting hydrogen bonds, but the hydrogens on nitrogen do not have a significant δ + , making amines poor hydrogen bond donors • Weak hydrogen bonding is evident in the low boiling point of ammonia (–33 °C) compared to H 2 O (100 °C) and the high boiling point compared to CH 4 (–161 °C) • The nitrogen of amines can be chiral only under very rare circumstances due to the low barrier of interconversion between enantiomers • Phosphines that are bonded to three different groups are chiral and configurationally stable because they have a much higher barrier of inversion • Amines cannot easily be prepared selectively by S N 2 displacement of an alkyl halide by another amine or NH 3 due to the occurance of polyalkylation • We have seen that nitrile reduction and the Hoffmann rearrangement are effective methods for forming primary amines • One strategy for selective amine synthesis is to use nitrogen-centered nucleophiles that
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