Gas phase chemistry of N-methyl 2- and 4-trimethylsilylmethylpyridinium ions 53 and 54 and the deuterated derivatives 104 and 105 were investigated using electrospray ionization (ESI) and tandem mass spectrometry. Collision induced ionization (CID) of the derived ions m/z 180 from both 53 and 54 gave rise to Me3Si+ at m/z 73 in addition to ions at m/z 108 and m/z 106 arising from competing proton transfer and hydride transfer pathways from within the initially formed ion-molecule-complexes. CID of the derived ions m/z 189 from the deuterated derivatives 104 and 105 gave rise to (CD3)3Si+ at m/z 82, in addition to ions at m/z 109 and m/z 106. Formation of the m/z 108 ions from 53 and 54 provides evidence to support the proposed mechanism for desilylation of β-silyl carbenium ions in solution. Computational studies at B3LYP/Gen (where 6-311g(d,p) was applied to C, H and N atoms, while SDD was applied to the metals: Si,Ge, Sn and Pb) support the MS studies as it was found that the favoured pathway is the proton transfer from the Me3Si+ ion to the basic enamine intermediate, giving rise to N-methyl-picoline and silylethene, followed closely by dissociation of the ion-molecule complex, with the least energetically favored pathway being hydride abstraction. Crystals of the cation 105 as its triflate salt, when heated at 160°C in a sealed tube for 2 days, gave rise to a mixture of N-methyl 4-CH3-pyridinium ion and N-methyl 4-CH2D-pyridinium ion, indicating that the proton transfer step also occurs in the condensed phase. A crystallographic and computation study on 2- and 4-trialkylgermylmethyl pyridinium ions 161 and 162 provided evidence for strong hyperconjugation between the Ge-CH2 bond and the π-deficient aromatic ring. Isodesmic equations show that the trimethylgermyl-substituent stabilizes the pyridinium cations by 20-26 kJ/mol relative to the germanium-free analogs. Natural bond orbital analysis reveals that the major contributor to this stabilization is hyperconjugation between the Ge-CH2 bond and the aromatic π-system, and that the strength of this interaction is greater for the 2-substituted ions 169 compared to the 4-substituted ions 170. Crystallographic analysis of the 2- and 4-tert-butylgermylmethyl- substituted ions x and x provides the first structural evidence for carbon-germanium hyperconjugation, thus the Ge-CH2 bonds are significantly longer (0.03-0.04 Å) than standard values and the CH2-Ar bond distance is shorter. Investigation of the gas phase unimolecular chemistry of these ions, formed via electrospray ionization (ESI) and subjected to collision induced dissociation (CID), reveals that the principle fragmentation of these ions involves cleavage of the weak CH2-GeR3 bond giving an ion molecule complex between an R3Ge+ and a pyridine-enamine, which then undergoes further rearrangement. Manifestation of the γ-effect can be seen in the crystals and theoretical structures by an increase in the Si-CH2 bond and a decrease in the CH2-CH2-C(Ar) bond angle of a range of trimethylsilylethyl-pyridinium ions (M = Si, Ge, Sn, Pb). The stabilization of the Group IV metals was found to be stronger at the β-position than at the γ-position. It was discovered that due to the tertiary nature of the cations, stabilization via a metal at the γ-position is not as pronounced as it would be if the stabilization of the primary or secondary cation were present. Computational studies on the trimethylsilylpropyl-pyridinium ions 394, 395 and 414-419 (M = Si, Ge, Sn, Pb) provide evidence for significant through-bond (double hyperconjugative) interaction between the M-CH2 bond and the low-lying π* orbital of the pyridinium ion. The strength of this interaction increases in the order Si < Ge < Sn < Pb in line with the σ-donor abilities of the C-M bond. The through-bond interaction for M = Si has been studied in solution using 13C and 29Si NMR studies, however the effect is small. Fragmentation pathways followed by these ions 394 and 395 in the gas phase under CID, is strongly influenced by the through-bond interaction and extrusion of ethylene occurs resulting in the formation of trimethylsilylmethyl-substituted pyridinium ions, 53 and 54, as the major fragmentation pathway.