C-H center dot center dot center dot X (where X = O or S) intramolecular hydrogen bonding is investigated in three benzyl Meldrum's acid derivatives using a combination of solution phase NMR spectroscopy, gas phase infrared multiple photon dissociation spectroscopy, and density functional theory calculations. In one compound, an abnormally large C-H center dot center dot center dot S hydrogen bond energy of 30.4 kJ mol(-1) is calculated with a natural bond orbital analysis. Intramolecular C-H center dot center dot center dot O hydrogen bonding is found to persist in the gas phase. Gibbs energy decomposition pathways are calculated.