To gain insight into the anisotropic sensitivity of shocked pentaerythritol tetranitrate ( PETN) single crystals, single-pulse Raman spectroscopy was used to examine the response of crystals shocked along the [100] ( insensitive) and [110] (sensitive) orientations. High-resolution Raman spectra revealed several orientation-dependent features under shock compression: (i) substantially different stress dependence of the Raman shift for the CH2 and NO2 stretching modes for the two orientations, (ii) discontinuity in the stress dependence of the Raman shift for the CH2 stretching modes above 4 GPa for the [110] orientation, and (iii) large broadening for the CH2 and NO2 asymmetric stretching modes for stresses above 4 GPa for the [110] orientation. The present data in combination with previous static pressure results provide support for conformational changes in PETN molecules for shock compression along the [110] ( sensitive) orientation. Implications of the present results for the anisotropic sensitivity of shocked PETN are discussed.