The crystal and molecular structures of the potential antidepressant drug fenobam and its derivatives are examined in terms of the preferred form among the two possible tautomeric structures. In this study, chemical derivatization has been utilized as a means to "experimentally simulate" the tautomeric preference and conformational variability in fenobam. Eight new derivatives of fenobam have been synthesized, and structural features have been characterized by single-crystal X-ray diffraction and NMR spectroscopy. The specific tautomeric preference found in all of these compounds and their known crystal forms have been construed in terms of the stabilizing intramolecular N−H•••O and N−H•••S hydrogen bonding. The hierarchy of intramolecular hydrogen bonds evidenced as the preference of the C−H•••O hydrogen bond over C−H•••N and that of the C−H•••N hydrogen bond over C−H•••S explains the two distinct conformations adopted by fenobam and thiofenobam derivatives. The relative energy values of different molecular conformations have been calculated and compared.

Functional test sequences are used in testing to target faults that are not detected by structural test. However, evaluating the stuck-at fault coverage of the functional test sequence by the gate-level fault simulation can be very time consuming. To obtain a fast estimation of the fault coverage, we describe a metric to grade the test sequence using Instruction-Execution graph. The metric is based on the set of registers the circuit traverses under the test sequence. Using this information in combination with the observability and controllability of the register, the test sequence is graded. Experimental results on Parwan processor show the effectiveness of the metric in ranking the test sequence based on their fault coverage.