<p>Mass spectrometry (MS) is a versatile analytical tool that is especially useful for identification of unknown compounds in mixtures when coupled with chromatography. In MS experiments, the analytes are ionized, separated based on their mass-to-charge (<i>m/z</i>) ratios, and detected. The molecular weight of the analyte can often be derived from the mass spectrum if stable molecular ions (M^•+) or stable protonated/deprotonated analyte molecules ([M+H]⁺ or [M-H]^–) are generated. Further, MS can also be used to obtain structural information for the ionized analytes via their fragmentation reactions. Tandem mass spectrometry (MSⁿ) experiments are powerful for the characterization of unknown compounds in mixtures without the need for coupling them with chromatography. In MSⁿ experiments, the analytes are ionized, the ions of interest are isolated and subjected to reactions, such as collision-activated dissociation (CAD) or ion-molecule reactions with neutral reagent molecules. The fragmentation pattern or the diagnostic ion-molecule reaction product ions can be utilized to elucidate the structures of the analytes. The fragment ions or diagnostic product ions can further be subjected to CAD to obtain more structural information. Besides analytical purposes, MSⁿ also provides a powerful tool for exploring the reactivities of reaction intermediates that are elusive, such as phenylcarbyne anions and phenylcarbene anions.</p> <p>The research described in this dissertation mainly focuses on the development of MSⁿ methods based on diagnostic gas-phase ion-molecule reactions followed by CAD for (1) the characterization of differently substituted ureas and (2) the differentiation of sulfonate esters from their isomeric analogs, such as sulfite esters and sulfones. HPLC was coupled with the MSⁿ methods discussed above to demonstrate its usefulness in the identification of compounds in mixtures. Additionally, a gas-phase reactivity study on phenylcarbyne anions is discussed in this dissertation. The phenylcarbyne anions were generated by CAD of two nitrogen molecules from negatively charged phenyl tetrazole precursors. Their reactivities towards various reagents were explored and rationalized with the help of quantum chemical calculations.</p>