[Figure not available: see fulltext.] N,O-Diprotonated forms (dications) of various quinolinecarbaldehydes were theoretically studied by DFT calculations. It was found that the most reactive electrophilic dications are expected to be generated from 2- and 4-quinolinecarbaldehydes compared to the other quinolinecarbaldehydes. Experimental studies of protonation of quinoline-2(6,8)-carbaldehydes in Brønsted acids (CF₃SO₃H, H₂SO₄) by means of ¹H, ¹³C, and ¹⁵N NMR revealed the formation of the corresponding N-protonated O-protosolvated species. Reactions of quinoline-2(6,8)-carbaldehydes with arenes in the presence of Brønsted (TfOH) and Lewis acids (AlX₃, X = Cl, Br) or acidic zeolites led to the formation of the corresponding 2(6,8)-(diarylmethyl)quinolines. However, 6- and 8-quinolinecarbaldehydes gave additionally unusual products – 6(8)-(arylmethyl)quinolines.