A compound for use in a method of treating a mitochondrial disorder, which compound is selected from the group consisting of: (a) compounds of formula X-O, formula X-R, formula XII-O, and formula XII-R: where R 11, R 12, and R 13 are independently selected from the group consisting of H, -C 1 -C 4 alkyl, -C 1 -C 4 haloalkyl, -CN, -F, -Cl, -Br, and -I, with the proviso that if any of R 11, R 12, or R 13 is H, then at least one of the other two substituents is neither H nor methyl; and all stereoisomers, mixtures of stereoisomers, solvates, and hydrates thereof; and (b) compounds of formula VII-O, formula VII-R, formula IX-O, and formula IX-R: where R 1, R 2, and R 3 are independently selected from -C 1 -C 4 alkyl, with the proviso that at least one of R 1, R 2, and R 3 is not methyl; and all stereoisomers, mixtures of stereoisomers, solvates, and hydrates thereof; wherein the method comprises administering a therapeutically effective amount of the compound; and wherein the mitochondrial disorder is selected from the group consisting of Leber's Hereditary Optic Neuropathy (LHON); Leigh Disease; Mitochondrial Myopathy, Encephalopathy, Lactacidosis, Stroke (MELAS); Kearns-Sayre Syndrome; Friedreich's Ataxia; inherited mitochondrial diseases; Myoclonic Epilepsy with Ragged Red Fibers (MERRF); other myopathies; cardiomyopathy; encephalomyopathy; renal tubular acidosis; neurodegenerative diseases; Parkinson's disease; Alzheimer's disease; amyotrophic lateral sclerosis; motor neuron diseases; other neurological diseases; epilepsy; genetic diseases; Huntington's Disease; mood disorders; schizophrenia; bipolar disorder; age-associated diseases; macular degeneration; and diabetes. (a) compounds of formula X-O, formula X-R, formula XII-O, and formula XII-R: where R 11, R 12, and R 13 are independently selected from the group consisting of H, -C 1 -C 4 alkyl, -C 1 -C 4 haloalkyl, -CN, -F, -Cl, -Br, and -I, with the proviso that if any of R 11, R 12, or R 13 is H, then at least one of the other two substituents is neither H nor methyl; and all stereoisomers, mixtures of stereoisomers, solvates, and hydrates thereof; and (b) compounds of formula VII-O, formula VII-R, formula IX-O, and formula IX-R: where R 1, R 2, and R 3 are independently selected from -C 1 -C 4 alkyl, with the proviso that at least one of R 1, R 2, and R 3 is not methyl; and all stereoisomers, mixtures of stereoisomers, solvates, and hydrates thereof; wherein the method comprises administering a therapeutically effective amount of the compound; and wherein the mitochondrial disorder is selected from the group consisting of Leber's Hereditary Optic Neuropathy (LHON); Leigh Disease; Mitochondrial Myopathy, Encephalopathy, Lactacidosis, Stroke (MELAS); Kearns-Sayre Syndrome; Friedreich's Ataxia; inherited mitochondrial diseases; Myoclonic Epilepsy with Ragged Red Fibers (MERRF); other myopathies; cardiomyopathy; encephalomyopathy; renal tubular acidosis; neurodegenerative diseases; Parkinson's disease; Alzheimer's disease; amyotrophic lateral sclerosis; motor neuron diseases; other neurological diseases; epilepsy; genetic diseases; Huntington's Disease; mood disorders; schizophrenia; bipolar disorder; age-associated diseases; macular degeneration; and diabetes.