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Keywords:

  • frequency shift;
  • NMR chemical shift;
  • glycine dipeptide;
  • C5 and C7 conformation

Abstract

A formamide molecule is allowed to form a CH···O H-bond with a glycine dipeptide in both its C5 and C7 internal conformations. As this intermolecular H-bond is elongated, the contraction of the C[BOND]H covalent bond is monitored, as is its vibrational stretching frequency and intensity, along with NMR chemical shifts of the atoms involved in the H-bond. The degree of shortening of the C[BOND]H bond becomes progressively smaller as the proton acceptor is moved further away, as does the blue shift of the C[BOND]H stretching frequency, and the chemical shift of the bridging proton. These changes are monotonic and regular enough that experimental evaluation of C[BOND]H bond length or blue shift or proton NMR chemical shift may be used to accurately predict the energetics of the H-bond for any particular geometry. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010