Density functional theory calculations are performed to assess the influence of confinement on the strength of H F hydrogen bond in (HF)(2)@C-n (n= 60, 70, 80, 90). The (HF)(2) entrapping process into C-60 cage is thermodynamically unfavorable whereas it is favorable in other cages. The hydrogen bond is shorter in confined cages than that in free dimer. The interaction energy between two HF units is maximum in Cgo whereas the bond is the shortest in C-70. It appears that in confined situation a shorter bond does not necessarily mean a stronger bond. Energy decomposition analysis and electron density analysis are performed to explain the results. (C) 2014 Elsevier B.V. All rights reserved.