Hydrazine - Molecular Structure and Properties

Molecular Structure and Properties

Hydrazine forms a monohydrate that is more dense (1.032 g/cm3) than the anhydrous material.

Hydrazine can arise via coupling a pair of ammonia molecules by removal of one hydrogen per molecule. Each H₂N-N subunit is pyramidal in shape. The N-N distance is 1.45 Å (145 pm), and the molecule adopts a gauche conformation. The rotational barrier is twice that of ethane. These structural properties resemble those of gaseous hydrogen peroxide, which adopts a "skewed" anticlinal conformation, and also experiences a strong rotational barrier.

Hydrazine has basic (alkali) chemical properties comparable to those of ammonia:

N₂H₄ + H₂O → + + OH−

with the values:

K_b = 1.3 x 10−6

pK_a = 8.1

(for ammonia K_b = 1.78 x 10−5)

Hydrazine is difficult to diprotonate:

+ + H₂O → 2+ + OH− K_b = 8.4 x 10−16

The heat of combustion of hydrazine in oxygen (air) is 194.1 x 105 J/kg (9345 BTU/lb).