We have carried out DFT studies to explore the cause of anomalously fast reaction rates of ethyl group (R = Et) in the gas-phase S(N)2 reactions of RCH2Cl+Cl- and RCH(CN)Cl+Cl-, and also for those in the cationic forms of RCH2+ and RCH(CN)(+) with R = Me, Et, i-Pr, and t-Bu. The TS stabilization by hyperconjugative donor-aceptor vicinal charge transfers (CTs) from R to the major NBOs at the reaction center carbon in the S(N)2 TSs were estimated using natural bond orbital (NBO) analyses. In all cases the hyperconjugative CT stabik.zation increases in the order R = t-Bu < i-Pr < Me < Et in agreement with the experimental as well as theoretical rate orders, exhibiting an ethyl anomaly. We have also determined the reorganization energies and hyperconjugative CTs from R to the two major NBOs, C-O- and C-N+, in the tetrahedral intermediate formed with five water molecules, T-5w, by transformation of sp(2) to sp(3) centers in the reactions of RC(=O)OC6H5 with NH3. The reorganization energy is the lowest and CT stabilization is the strongest with R = Et in line with the fastest experimental rate. We conclude that C-H it a better donor than C-C bond orbital and hyperconjugative vicinal sigma chain extension leads to a stronger CT stabilization in the TS. The stronger CT stabilization for R = Et rather than Me is achieved by enhanced hyperconjugative CT to the reaction center in the TS as a result of narrower energy gap and greater overlap brought about by long-range orbital mixing as the C-H sigma-chain is extended from n = 2 for Me to n = 3 for Et. We find that CT properties of the all-trans vicinal hyprconjugative C-H sigma-chains are closely analogous to the corresponding conjugative polyene pi-chains although skeletal patterns of bridge bonds are different and the stabilization energy gained by extension of the sigma-chain is much weaker than that gained by the pi-chain.