hydrogenationhydrogenolysishydrogxyl grouphydrolysishydronium ionhydrophilichydrophilic compoundhydrophobehydrophobic compoundhydroquinolhydroquinonehydrotreatinghydroushydrous salthydroxidehydroxonium ionhygrometerhygroscopehygroscopichygroscopic resinhyperconjugationhyperfinehyperfine structurehypnotichypothesishysteresis