Energetics, proton transfer rates, and kinetic isotope effects in bent hydrogen bonds

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N-N...N H-bonds which occur in intermolecular contacts and in intramolecular situations where the bond is bent are investigated by ab initio methods. Distortion of the O(N-H...N) angle of up to 40 o from linearity results in modest increases in the barrier to proton transfer while a much higher barrier occurs in NH 2 CH 2 NH 3 + where this angular distortion is some 100 o . The rate of transfer is orders of magnitude slower in the latter system. In contrast to earlier suppositions that systems containing nonlinear H-bonds are subject to smaller kinetic isotope effects, k H /k D for the most highly strained system is larger than in other complexes