Tertiary amines lack intermolecular association as they do not have hydrogen atoms available for hydrogen bond formation. Consequently, the order of boiling points among isomeric amines is Primary > Secondary > Tertiary.
Why do tertiary amines lack intermolecular association, and how does this affect their boiling points compared to primary and secondary amines?
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Tertiary amines lack intermolecular association because they lack a hydrogen atom directly attached to the nitrogen, essential for hydrogen bonding. Intermolecular forces in tertiary amines are limited to weaker London dispersion forces. Consequently, tertiary amines have lower boiling points than primary and secondary amines, which can engage in hydrogen bonding. The absence of strong hydrogen bonds in tertiary amines reduces the energy required to overcome intermolecular forces, resulting in lower boiling points. Primary and secondary amines, with the capacity for hydrogen bonding, exhibit higher boiling points due to the additional energy needed to break these stronger intermolecular attractions.