Restricted rotation about the N-N single bond Linear correlation of rate with substituent

Reactions of organolithium reagents with quinazoline derivatives

“…Orthogonal conformations are known to be significantly more stable than their co-planar counterparts for N,N'-diacylhydrazines, which has resulted in measured barriers to rotation about the N-N bond. 129,130 Barriers to rotation have been reported for di-and tetraacylhydrazines, where both nitrogen atoms are of amide type, [131][132][133][134] hydrazines, 135 triazines 136 and tetrazines. 137 Also, hindrance to rotation about the N-N bond in 3-acylamino-and 3-diacylamino-3H-quinazolin-4-ones was found to be as high as for hydrazine derivatives (14.7-20.6 Kcal mol -1 ).…”

Hyperbranched Poly(triazene ester)s as Novel Globular Photolabile and Thermolabile Polymers

“…Similar effects were observed for 1-aryl-3,3-dialkyltriazenes at low temperatures and Scheme 3. were subject to studies in the past. [33,34] The authors could show that the triazene group exists as the sterically less hindered trans isomer. However, hindered internal rotation on the N 2 , N 3 bond was observed due to formation of a 1,3-dipolar structure (Scheme 4).…”

Rotation about Single Bonds in Organic Molecules

“…Interestingly, the barrier to rotation of the nitroso group in XLIII (X = N) is significantly higher (AG*_23°c = 14.2 ± 0.2 kcal/mole, Dunlop et al, 1971) than in /?-nitroso-7V,7V-dimethylaniline, suggesting more efficient back-donation of the lone pair on the nitrogen atom due to steric constraint. Nuclear magnetic resonance data of some relevance to the problem of restricted rotation in aromatic nitroso derivatives are also given by Calder et al (1967), Norris andMatsubayashi et al (1970).…”