*Review* **Molecular Tailoring Approach for the Estimation of Intramolecular Hydrogen Bond Energy**

**Milind M. Deshmukh 1,\* and Shridhar R. Gadre 2,\***

	- Pune 411007, India

**Abstract:** Hydrogen bonds (HBs) play a crucial role in many physicochemical and biological processes. Theoretical methods can reliably estimate the intermolecular HB energies. However, the methods for the quantification of intramolecular HB (IHB) energy available in the literature are mostly empirical or indirect and limited only to evaluating the energy of a single HB. During the past decade, the authors have developed a direct procedure for the IHB energy estimation based on the molecular tailoring approach (MTA), a fragmentation method. This MTA-based method can yield a reliable estimate of individual IHB energy in a system containing multiple H-bonds. After explaining and illustrating the methodology of MTA, we present its use for the IHB energy estimation in molecules and clusters. We also discuss the use of this method by other researchers as a standard, state-of-the-art method for estimating IHB energy as well as those of other noncovalent interactions.

**Keywords:** hydrogen bond (HB); intramolecular hydrogen bond (IHB); molecular tailoring approach (MTA); fragmentation methods; bond energy estimation; noncovalent interactions
