The primary aim of this dissertation was to seek the answer to the question: “Is the single transition-state model appropriate for the fundamental reactions in organic chemistry?” The goal was accomplished by performing enormous kinetic data collection and detailed mechanistic analysis on several typical fundamental organic chemical reactions. Three new methodologies for differentiating between a simple one-step and complex multi-step mechanism were developed and extensively confirmed during the application in the kinetic studies of all of the reaction discussed in this dissertation. The three methods consist of (1) half-life dependence of kapp, (2) sequential linear pseudo-first-order correlation, and (3) revised instantaneous rate constant analysis. A detailed kinetic investigation of the formal hydride transfer reaction of NADH models [N-benzyl-1,4-dihydronicotinamide (BNAH) with Nmethylacridinium (MA+) and N-methyl-9,10-dihydroacridine (MAH) with tropylium ion (Tr+)] confirmed that both these reactions take place in more than one step and involve kinetically significant reactant complex intermediates, which are noncovalentlly bound intermediates. Computations at the M06-2x/6-311++G(d,p) level provided the structure of the reactant complex intermediate. A reinvestigation of the formal hydride transfer reaction of 1-benzyl-3- cyanoquinolinium ion (BQCN+) with N-methyl-9,10-dihydroacridine (MAH) in acetonitrile (AN) confirmed that the reaction takes place in more than one step and revealed a new mechanism that had not previously been considered. It was observed that even residual oxygen under glove box conditions initiates a chain process leading to the same products. The combination reactions studied include the reaction between a carbocation and an anion as well as the reaction of trans-β-nitrostyrene with nitroethide ion. Conventional pseudo-first-order analysis as well as instantaneous rate constant analysis confirmed that the combination reactions do not follow the simple one-step mechanism. The SN2 displacement of halide ions by the 4- nitrophenoxide ion was also investigated and the kinetic data are inconsistent with the concerted single transition-state model.