The accessibility of all possible reaction paths for the reaction between the nucleobase adenine and the •OH radical is investigated through quantum chemical calculations of barrier heights and rate constants at the wB97X-D/6-311++G(2df,2pd) level with Eckart tunneling corrections. First the computational method is validated by considering the hydrogen abstraction from the heterocyclic N9 nitrogen in adenine as a test system. Geometries for all molecules in the reaction are optimised with four different DFT exchange-correlation functionals (B3LYP, BHandHLYP, M06-2X and wB97X-D), in combination with Pople and Dunning basis sets, all of which have been employed in similar investigations in the literature. Improved energies are obtained through single point calculations with CCSD(T) and the same basis sets, and reaction rate constants are calculated for all methods both without tunneling corrections and with the Wigner, Bell and Eckart corrections. Compared to CCSD(T)//BHandHLYP/aug-cc-pVTZ reference results, the wB97XD/6-311++G(2df,2pd) method combined with Eckart tunneling corrections provides a sensible compromise between accuracy and time. Using this method all sub-reactions of the reaction between adenine and the •OH radical are investigated. The total rate constants for hydrogen abstraction and addition for adenine are with this method predicted to be 1.06×10−12cm3molecules−1s−1 and 1.10×10−12cm3molecules−1s−1, respectively. Abstractions of H61 and H62 contribute most, while only addition onto the C8 carbon is found to be of any significance contrary to previous claims that addition is the dominant reaction pathway. The overall rate constant for the complete reaction is found to be 2.17×10−12cm3molecules−1s−1, which agrees exceptionally well with experimental results.